Colored Polymer-reinforced Metal-organic Framework Microparticles with High Charge-to-mass Ratio for Electrophoretic Display

Colored Polymer-reinforced Metal-organic Framework Microparticles with High Charge-to-mass Ratio for Electrophoretic Display | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Colored Polymer-reinforced Metal-organic Framework Microparticles with High Charge-to-mass Ratio for Electrophoretic Display Hao Li, Jiamin Cheng, Mian Qin, Wenhao Wang, Jingxing Zhang, Yao Wang, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6249755/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Feb, 2026 Read the published version in Light: Science & Applications → Version 1 posted 10 You are reading this latest preprint version Abstract Besides high porosity and controllable structure, metal-organic framework (MOF) has some natural advantages for color electrophoretic particles: easy modification, controllable morphology, low and adjustable density, and high charge density, as well as rich, vivid, and stable colors. Therefore, we first integrated the four colored MOF microparticles and polyelectrolytes into the blue, reddish-brown, green, and purple electrophoretic particles, to construct the two-color stable dispersions in nonpolar isododecane as the electrophoretic inks. Here the surface modification of polyethyleneimine (PEI) chains based on non-covalent interaction rendered these MOF microparticles reinforced fully to ~ + 30 mV in Zeta potential and over 3.6×10 − 10 m 2 /V·s in the electrophoretic mobility. Under the ultralow field strength of 0.02 V/µm, all the response time and recovery time were no more than 2.3 and 5.9 seconds, respectively. Even after long-time or multiple driving, these MOF microparticles and their reflectance value still kept constant to some extent. By comparison, these colored PEI-reinforced MOF microparticles are superior to the other organic color pigments and inorganic particles, in response capability, charge-to-mass ratio, preparation method, production cost, and stability in color, particle and display. It is anticipated to provide an innovative and promising technical path for color electrophoresis display. Physical sciences/Optics and photonics/Optical materials and structures/Nanoparticles Physical sciences/Optics and photonics/Applied optics/Displays Metal-organic framework Polymer-reinforced Color particle High charge density Electrophoretic display Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction As a promising type of porous crystalline hybrids, metal-organic frameworks (MOFs) are assembled by coordination between inorganic metal ions and organic ligands 1 , 2 . By variation of the two key components enable MOFs to be infinitely devolved into diverse chemical and physical properties 3 , 4 . So besides high specific surface area and porosity, MOFs feature both controllable structure and function, and have been widely used in the fields of catalysis, adsorption, separation, sensing, drug delivery and so on 5 , 6 . In particular, MOFs exhibit unique charge characteristics of inorganic-organic hybrids. The overall charge of the framework can be tuned with the oxidation state of metal ions within the ligand 7 , ZIF-8, ZIF-67, MIL-101(Cr), and MOF-801 were proved to be positively charged 8 . From the perspective of electrophoretic particle, MOFs have few natural advantages: (1) more options for organic functional groups to allow exquisite modification 2 , 9 ; (2) good morphology controllability, including wide variation of sizes ranging from micrometer to nanometer scale, and structures changing from three to zero dimensional 10 ; (3) low and adjustable density, for example, the proven density of HKUST-1 changing from 0.883, 1.07, to 2.8 g/cm 3,11, 12 . The third virtue is very beneficial for improving migration rate and multiparticle resolution 13 . In addition, rich, vivid, and stable colors of MOFs provide more possibilities for fine patterning and color electrophoretic display (EPD). Undoubtedly, MOFs are much lighter and more colorful than other inorganic electrophoretic particles (e.g. metal ion-doping TiO 2 nanoparticle) 14 , 15 , and much easier to be modified, and more stable in color than common organic ones (e.g. color dye/pigment particles) 13 , 16 , 17 . But MOFs still need less aggregation, higher charge density, better stability and compatibility, to meet the requirements of high-performance display 17 . In general, a good way is polymer modification on the MOF surface via. covalent anchoring or physical adsorption 8 , 18 . In our work, 1,3,5-benzenetricarboxylic acid (BTC) as a common organic ligand was coordinated with Cu 2+ , Fe 3+ , Ni 2+ , and Co 2+ ion by solvothermal method, to form the blue, reddish-brown, green, and purple MOF (M-BTC) microparticles (i.e., Cu-BTC, Fe-BTC, Ni-BTC and Co-BTC), respectively (see Fig. 1 ). And these resulting M-BTC microparticles were further reinforced by physically adsorbed polyethyleneimine (PEI) for stronger electrophoretic performances. Here PEI with a high amine density is easily localized on the surface of MOF microparticle through electrostatic interaction and hydrogen bonding. It not only makes the MOF structure more stabilized, but also endows the MOF surface with abundant amino groups to improve charge density. In addition, isododecane, an oil phase with ultralow polarity was chosen as electrophoresis medium, to effectively avoid possible MOF decomposition/transformation. Results As a truly mainstream reflective paper-like display, EPD has some distinct advantages, e.g. quick response, bistable state, high reliability, wide viewing angle, and low cost and power consumption, but is greatly limited by color and video 19 – 21 . Although it is technically easy to colorize EPD using color filters, it comes at the expense of display brightness and resolution, as well as device thickness 22 . So EPD is still facing a huge challenge on high-performance colored electrophoretic particles. We first integrated light and colorful MOF microparticles and polyelectrolyte functionalization into charged colloid particles, to develop a novel colored- electrophoretic particle. These MOFs represent four metals widely used in MOF synthesis: Cu, Fe, Ni, Co. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images (Fig. 2 and Figure S1 ) demonstrated the morphology of M-BTC and M-BTC-PEI. As shown in Fig. 2 A and 2 B, those crude Cu-BTC microparticles were regular octahedra with uniform size of about 700 nm, and those PEI-modified Cu-BTC-PEI microparticles presented in similar but adherent morphology. In Fig. 2 C and 2 D, the blank Fe-BTC microparticles took a large agglomerate look comprising many irregular polyhedrons with a size of about 100 nm, and did not change much after PEI modification. It can be seen from in Fig. 2 E and 2 F that, those original Ni-BTC microparticles appeared in rough microsphere with an average size of about 2 µm, and those PEI-modified ones almost remained unchanged. By comparison, both the Co-BTC and the Co-BTC-PEI microparticles were nano/micron disordered nanosheets in Fig. 2 G and 2 H. Evidently, all the above-mentioned MOF microparticles were completely consistent with what has been previously reported. And there was almost no change in morphology before and after PEI modification, indicating that the adsorbed PEI chains were limited. This was also confirmed by the energy dispersive spectroscopy (EDS) of Cu-BTC & Cu-BTC-PEI (see Fig. 2 I and 2 J) and Ni-BTC & Ni-BTC-PEI (see Figure S2 ). Hereinto, a slight increase in nitrogen content showed the successful PEI modification on these M-BTC microparticles. The powder x-ray diffraction (XRD) patterns of the resulting M-BTC and M-BTC-PEI microparticles in the 2θ angle region at 5 ~ 70◦ were illustrated in Fig. 3 A. Apparently, all the diffractograms before and after PEI modification were almost identical and in good agreement with the results previously reported in the literature, showing good crystalline. These major diffraction peaks were listed as below: Cu-BTC, 6.8° (200), 9.5° (220), 11.63° (222), 13.53° (400), 14.7° (331), 15.03° (420), 16.47° (422), 17.52° (333), 19.11° (440), 20.26 ° (600), 24.11° (711), 26.10° (553), 29.37° (662), and 35.3° (951); Fe-BTC, 7.1° (440), 10.3° (660), 11.07° (428) ,12.65° (1022), 14.3° (088),20.16°(4814), 24.1° (6618) and 27.78°(9321); Ni-BTC, 12.2° (2–10), 15.33° (002), 18.0° (300), 20.9°, 22.32°, 23.88°, 26.13° (2–13), and 27.9° (5–10); Co-BTC, 2 θ value of 10.92° (200), 14.6° (001), 18.8° (111), 20.1° (021), 24.69° (13 − 1), 25.36° (42 − 1), 27.19° (20 − 2), 33.9° (62 − 1), 35.43◦ (440). The Fig. 3 B exhibited the characteristic functional groups of different M-BTC and M-BTC-PEI composites. In these Fourier-transform infrared spectra (FT-IR), few similar peaks at 750, 1360 ~ 1450, and 1550 ~ 1670 cm - 1 , were attributed to symmetric, asymmetric stretching vibrations of C = C, C-O, and C = O bonds in the BTC ligands, respectively. And the representative absorption peaks at 725, 615, 720, and 720 cm - 1 corresponded to the vibrational peaks of the intrinsic coordination bonds between oxygen atom (O) and metal ion (i.e., Cu 2+ , Fe 3+ , Ni 2+ and Co 2+ ). But significant difference before and after PEI modification cannot be found, which may be attributed to the absorption overlap of the amino groups (N-H; 3100 ~ 3500 cm - 1 ) with the hydroxy groups (-OH) of residual alcohol or water (300 ~ 3500 cm - 1 ). So we performed high-temperature tests using variable temperature attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), to eliminate possible interference from the residual. Just as shown in Fig. 3 B ~ 3E , all the N-H peaks of the resulting M-BTC-PEI microparticles still emerged clearly in the range from 3100 to 3400 cm - 1 , indicating successful PEI adsorption on the surface of M-BTC. In addition, Fig. 3 G and 3 H further exhibited the chemical states and compositions of Cu-BTC and Cu-BTC-PEI microparticles. Obviously, the C 1s, O 1s, and Cu 2p peak kept constant, and the N 1s peak was enhanced after PEI modification, indicating the successful bonding of PEI chains. Correspondingly, both the binding energies of the carbonyl group (C = O) and the carbon-oxygen bond (C-O) in BTC ligands also increased with 0.59 eV. This red shift may be attributed to the newly formed hydrogen bonds between oxygen atom and amino groups of PEI chain (N-H∙∙∙O). The thermogravimetric (TGA) curves of the resulting M-BTC and M-BTC-PEI microparticles were recorded in Fig. 4 . Apparently, all the M-BTC microparticles before and after PEI modification, behaved with almost the same residual masses but the different thermolytic behaviors. The first stage of weight loss below 150 ℃ undoubtedly originates from the removal of the residual solvent (e.g. water, ethanol, and DMF). The differences in thermolysis were mainly manifested in the subsequent process (see Figure S3 ). It is well-known that, the decomposition range of the crude BTC molecules is normally between 300 and 350 ℃ 23 , 24 , and broadened to higher temperature after coordination with metal ions 24 , 25 . This embodied well in the thermogravimetric curves of these M-BTC microparticles above 300 ℃. And the thermolysis of PEI also occurs in the temperature range between 300 and 350 ℃ 26 – 28 . Hence, in the main stage of weight loss between 150 and 500 ℃, those modified PEI chains visibly made M-BTC-PEI microparticles decomposed slightly faster than the crude M-BTC microparticles (see Figure S3 ). Although the accurate mass of PEI in the M-BTC-PEI microparticles is very difficult to be determined, its existence can be confirmed. Of course, the reinforcing effect of PEI modification is more reflected from the colloidal nature of the M-BTC-PEI microparticle. In Fig. 5 and S4, all the Zeta potentials of the M-BTC microparticles were around 10 mV, which was caused by the exposed carboxyl groups on the MOF surface. To M-BTC-PEI microparticles, the abundant protonated amino groups of the linked PEI chains inevitably enabled these microparticles to convert into being positively charged. At the same PEI feed of 20 wt.%, different molecular weights of PEI brought about different Zeta potential. Hereinto, PEI with the molecular weight of 10,000 g/mol was viewed as the best option, whose corresponding Zeta potential was slightly higher than the ones’ with the molecular weight of 25,000 g/mol. It seems that, larger random coil of the latter may be unfavorable for PEI bonding and adsorption. As the molecular weights of PEI was settled as 10, 000 g/mol, all the maximum Zeta potential of the M-BTC-PEI microparticles emerged around + 30 mV at the same PEI feed of 30 wt.%. Similarly, higher feed above the saturated bonding point may be not helpful for improving surface potential. Meanwhile, such variation in Zeta potential also appeared in mobility (see Table 1 ). So the optimized parameters of PEI modification for those electrophoretic M-BTC-PEI microparticles were chosen as: the molecular weight of PEI was 10,000 g/mol, and the feed of PEI was 30 wt.%. Naturally, this surface PEI decoration consequentially made these M-BTC microparticles bigger with wider size distribution, just shown in Figure S5 and Table 1 . In addition, we attempted to utilize negatively charged polyacrylic acid (PAA) and uncharged polyethylene glycol (PEG) to modify the surface of the M-BTC microparticles using the same non-covalent bonding. As shown in Figure S6 , plentiful carboxyl groups of the bonded PAA chains further rendered those resulting M-BTC-PAA microparticles more negatively charged to about − 30 mV. Similarly, plentiful hydroxyl groups of the bonded PEG chains only leaded to a slight decrement of the Zeta potential of those resulting M-BTC-PEG microparticles. It is a sign that, this non-covalent “adsorption” (e.g. hydrogen bonding and electrostatic interaction) is suitable for various polymers, and applicable for adjusting the charge properties of the MOF surface. Table 1 Particle characteristics of blank PEI chains, M-BTC and M-BTC-PEI microparticles in isododecane. Sample Zeta potential (mV) Mobility (×10 − 8 m 2 /Vs) Effective Size (nm) Polydispersity PEI 1800 10.31 ± 1.07 0.014 ± 0.001 3.5 ± 0.21 0.525 ± 0.086 PEI 1W 13.51 ± 1.32 -0.018 ± 0.001 9.06 ± 0.03 0.225 ± 0.003 PEI 2.5W 15.41 ± 1.27 0.02 ± 0.001 9.41 ± 0.04 0.221 ± 0.024 Cu-BTC -14.89 ± 1.026 -0.01 ± 0.001 738.36 ± 9.88 0.265 ± 0.025 Cu-BTC-PEI 30% 27.51 ± 1.83 0.036 ± 0.003 782.44 ± 12.96 0.2815 ± 0.031 Fe-BTC -9.50 ± 1.19 -0.010 ± 0.001 734.84 ± 6.52 0.268 ± 0.026 Fe-BTC-PEI 30% 30.57 ± 2.48 0.041 ± 0.002 806.87 ± 13.64 0.330 ± 0.034 Ni-BTC -13.08 ± 1.20 -0.016 ± 0.003 1890.94 ± 29.56 0.351 ± 0.021 Ni-BTC-PEI 30% 36.11 ± 2.90 0.047 ± 0.003 2018.78 ± 74.41 0.385 ± 0.067 Co-BTC -3.91 ± 1.93 -0.009 ± 0.001 1270.70 ± 10.22 0.296 ± 0.031 Co-BTC-PEI 30% 35.54 ± 1.69 0.047 ± 0.01 1307.40 ± 22.40 0.321 ± 0.013 Note : In M-BTC-PEI 30%, PEI denoted the bonded PEI chain with the molecular weight of 10,000 g/mol, and 30% did the feed ratio of PEI. Subsequently, these PEI-reinforced MOF microparticles were dispersed with an acidic charge control agent (polyisobutenyl succinic anhydrides, PIBSA) into isododecane to formulate a series of colored electrophoretic inks. Figure 6 A showed that, all the reflectance spectra of the M-BTC-PEI inks agreed well with the real colors of the M-BTC-PEI microparticles. We further calculated their tristimulus values (i.e., X , Y , and Z ) according to the following formula (Eq. 1 ~ 5 ) and converted into chrominance coordinates. $$\:\begin{array}{c}X=\kappa\:\sum\:_{\lambda\:}{{\phi\:}}_{{\lambda\:}}\left({\lambda\:}\right)\stackrel{-}{{\chi\:}}\left({\lambda\:}\right)\varDelta\:\lambda\:\#\left(\text{E}\text{q}\text{u}\text{a}\text{t}\text{i}\text{o}\text{n}\:1\right)\end{array}$$ $$\:\begin{array}{c}Y=\kappa\:\sum\:_{\lambda\:}{{\phi\:}}_{{\lambda\:}}\left({\lambda\:}\right)\stackrel{-}{\mathcal{Y}}\left({\lambda\:}\right)\varDelta\:\lambda\:\#\left(\text{E}\text{q}\text{u}\text{a}\text{t}\text{i}\text{o}\text{n}\:2\right)\end{array}$$ $$\:\begin{array}{c}Z=\kappa\:\sum\:_{\lambda\:}{{\phi\:}}_{{\lambda\:}}\left({\lambda\:}\right)\stackrel{-}{\mathcal{Z}}\left({\lambda\:}\right)\varDelta\:\lambda\:\#\left(\text{E}\text{q}\text{u}\text{a}\text{t}\text{i}\text{o}\text{n}\:3\right)\end{array}$$ $$\:\begin{array}{c}\kappa\:=\frac{100}{\sum\:_{\lambda\:}\text{S}\left({\lambda\:}\right)\stackrel{-}{\mathcal{Y}}\left({\lambda\:}\right){\Delta\:}{\lambda\:}}\#\left(\text{E}\text{q}\text{u}\text{a}\text{t}\text{i}\text{o}\text{n}\:4\right)\end{array}$$ $$\:\begin{array}{c}\phi\:\left({\lambda\:}\right)=R\left({\lambda\:}\right)S\left({\lambda\:}\right)\#\left(\text{E}\text{q}\text{u}\text{a}\text{t}\text{i}\text{o}\text{n}\:5\right)\end{array}$$ where k is the normalization constant, Δλ is the wavelength interval (1 nm), S(λ) is the relative spectral distribution of the light source (D65), R(λ) is the reflectance of the sample under this light source, φ(λ) and φ λ (λ) are the relative color stimulus function and the color stimulus function, respectively, and φ(λ) can be used instead of φ λ (λ) for the reflected object color. So, we calculated out k and XYZ based on the standard value of S(λ) and the measured R(λ) , and obtained the color matching functions of the CIE 1931 standard chromaticity observer (i.e., x , y , and z ) by the corresponding formula, x = X / X + Y + Z , y = Y /X + Y + Z , and z = Z/ X + Y + Z . All the results, including the detailed CIE coordinate parameters, were finally plotted in Fig. 6 B, which also corresponds well to the real colors of the M-BTC-PEI microparticles. Given many polar groups on the surface of the M-BTC-PEI microparticles, a right amount of PIBSA as both dispersant and charge control agent, was added into nonpolar isododecane dispersion against possible aggregation. In particular, the long and flexible carbon chain of PIBSA has a spatial site-blocking effect to keep these electrophoretic microparticles away from each other. Just shown in Fig. 6 C and D , the ultraviolet-visible spectra (UV-Vis) absorbance of the Cu-BTC-PEI dispersion decreased slowly within 1 hour in an assisting effect of PIBSA, but the one without PIBSA cannot keep in a good dispersion even in 5 minutes. In this Cu-BTC-PEI/PIBSA formula, those colloid particles clearly exhibited good dispersibility in isododecane, especially low apparent density close to that of isododecane. This is also reflected in the corresponding object figures (see Fig. 6 E). Next, we verified the single particle electrophoresis system of M-BTC-PEI microparticles in PIBSA/isododecane for the first time. At a driving direct current (DC) voltage of 20 V, those M-BTC-PEI microparticles were visibly fixed on the side of the negative ITO electrode, and the other part became completely transparent while the electrophoresis plate tilted (see Figure S7 ). Apparently, these electrophoretic microparticles were positively charged. And we integrated the modified TiO 2 nanoparticles as representative white electrophoretic particles into this dispersion, to form a two-color electrophoretic ink. As shown in Figure S8 and Table S1 , the applied TiO 2 nanoparticles had few basic features: particle size, ~ 200 nm; Zeta potential, + 55.57 mV; electrophoretic mobility, 4.1×10 − 10 m 2 /(Vs). Here the Zeta potential is higher than that of the M-BTC-PEI microparticles, and surely make electrophoresis migration of the modified TiO 2 nanoparticles faster under the same driving situation. It may be effective to avoid possible adsorption, agglomeration, and precipitation of positive and negative particles during multiple electrophoresis to some extent. This two-color electrophoretic ink was poured into electrophoretic display cell, and then driven at an alternating DC voltage of ± 20 V (see Fig. 7 A) in daylight. Hereinto, response time ( T on ) and shutdown time of electrophoretic display ( T off ; also known as recovery time) were defined as the required time from baseline to 90% of reflectance maximum, and the one from 90% of reflectance maximum to baseline, respectively. Figure 7 B ~ E showed that, all the T on of the M-BTC-PEI/TiO 2 inks were less than 2.3 seconds, and all the T off were less than 5.9 seconds under the low field strength of 0.02 V/µm. Here high charge-to-mass ratio of the M-BTC-PEI microparticles based on high Zeta potential and low apparent density is the main reason of rapid response. Verly clearly, the Co-BTC-PEI/TiO 2 formula was the most effective: T on , 1.10 seconds; T off , 4.82 seconds. Because Co-BTC-PEI microparticle took the lead in charge density per unit volume and mobility: Zeta potential, 35.54 ± 1.69 mV; effective size, 1307.40 ± 22.40 nm; mobility, 4.7 ± 1×10 − 8 m 2 /Vs. In particular, both the reflectivity and the response speed were independent of the repetitive switching, indicating the good stability of this electrophoresis system. As well-known, contrast ratio ( CR ) is the ratio of the white reflectance value ( R w ) to the black reflectance value ( R b ), namely CR = R w / R b . In this study, the CR value is defined as the ratio of R w to the color reflectance value, and named as CR Cu−T , CR Fe−T , CR Ni−T , and CR Co−T according to the corresponding M-BTC-PEI/TiO 2 ink, respectively. It was drawn from Figs. 7 B ~ E that, CR Fe−T (1.37) > CR Cu−T (1.35) > CR Ni−T (1.23) > CR Co−T (1.16). By the comprehensive comparison of the four key parameters, i.e. T on , T off , CR , and color, the Cu-BTC-PEI/TiO 2 ink was viewed as the best option, while the Co-BTC-PEI/TiO 2 ink had the fastest response but the lowest CR value. In actual electrophoresis scenes, the real-time variations in chromaticity values of the M-BTC-PEI/TiO 2 inks were monitored using a colorimeter. As we can see from Fig. 8 , Video S1 , S2 , S3 , and S4 , the blue-white Cu-BTC-PEI/TiO 2 and the reddish-brown -white Fe-BTC-PEI/TiO 2 systems with high R w values were undoubtedly the best represented in display effect. First, the two-color coordinates were far away from the white point (0.33, 0.33). Second, both the Cu-BTC-PEI and Fe-BTC-PEI microparticles showed significantly behaved better with small size, regular morphology, and high color saturation (see Fig. 2 ). Third, both of them had high charge density per unit volume and mobility in the core electrophoretic index (see Table 1 ). By comparison, the purple-white Co-BTC-PEI/TiO 2 system did not perform well, which is mainly ascribed to its large size and irregular morphology 29 . Moreover, we collected and characterized those charged M-BTC-PEI microparticles on the electrophoretic plate after continuous power over 1 hour. In Figure S9 , the characteristic peaks of those MOF microparticles still remained, indicating the good structural stability after multiple electrophoresis in low dielectric liquid. And we also tested the four two-color M-BTC-PEI/TiO 2 electrophoretic systems after multiple driving cycles with a duration of 500 seconds were applied. Figure S10 exhibited that, both the Cu-BTC-PEI/TiO 2 and Fe-BTC-PEI/TiO 2 systems played with great consistency in reflectance. Only a slight decrement in reflectance and CR value appeared at the later cycles. It may result from possible aggregation of white TiO 2 nanoparticles with the colored M-BTC-PEI microparticles. Compared with the other color electrophoretic particles, these PEI-reinforced MOF microparticle that we first have distinct advantages in driving field strength and response time, just shown in Table 2 . And their low cost, facile preparation, high and high stability in color, particle and display, are also obviously superior to the other organic color pigments and inorganic particles. Table 2 Comparison of the electrophoretic characteristics of the reported color electrophoretic inks. Materials Zeta potential (mV) Electrophoretic mobility (10 − 8 m 2 /V·s) Average diameter (nm) Driving Voltage (V) / Spacing (µm) T on (s) Reference Fe/Co/Al-doped TiO 2 −102.14 −0.1048 286.8 30 V/~ 1.121 30 CuPcCl -26.8 \ 120 30 V/1000 µm 1.5 31 PY110/PS PY118/PE -60~-70 -30-40 \ 500 300 15 V/1000 µm 2 4 32 BAM-MPS-PLMA −63.73 \ 700 30 V/~ 0.17 33 RYB-poly(styrene-co-4-VP) -40 -2.89×10 − 2 800 20 V/100 µm \ 34 PY13- PR254 PB15 -3.45 -31.83 -0.45 -8.269×10 − 3 -7.631×10 − 2 -1.076×10 − 3 217.7 155.2 80.3 100 V/1000 µm 1s 0.8s 0.5s 35 TiO 2 -OTS/P(4-VP-co-LA21) -3.6 ± 1 -2.5×10 − 2 435 ± 16 50 V/100 µm 0.416 36 PB-IL235 + 71.46 + 1.64 263 ~ 438 \ \ 37 Fe 3 O 4 @SiO 2 -55.9 \ 101 ~ 177 2.5 V/50 µm 0.472 38 PIL/SCAs + 4.13 + 6.17×10 − 2 188 20 V/~ 0.165 39 Cu-BTC-PEI Fe-BTC-PEI Ni-BTC-PEI Co-BTC-PEI + 27.51 + 30.57 + 36.11 + 35.54 + 3.6×10 − 2 + 4.1×10 − 2 + 4.7×10 − 2 + 4.7×10 − 2 782.44, 806.87, 2018.78, 1327.40 20 V/1000 µm 2.16 1.14 2.28 1.10 This work Note : To M-BTC-PEI, PEI was the bonded PEI chains with the molecular weight of 10,000 g/mol, and the feed ratio of 30 wt.%. Discussion In summary, we integrated the four colored MOF microparticles and polyelectrolytes into the blue, reddish-brown, green, and purple electrophoretic particles for the first time. In particular, the surface modification of PEI chains based on non-covalent interaction rendered these M-BTC microparticles reinforced fully: the Zeta potential rose from ~-10 to ~ + 30 mV; the electrophoretic mobility grew up from ~ 1.0×10 − 10 to over 3.6×10 − 10 m 2 /V·s. The colored M-BTC-PEI microparticles further paired with the representative white TiO 2 nanoparticle to form the two-color stable dispersions in nonpolar PIBSA/isododecane as the electrophoretic inks. Under the ultralow field strength of 0.02 V/µm, all the response time and recovery time were no more than 2.3 and 5.9 seconds, respectively. Even after long-time or multiple driving, these MOF microparticles and their reflectance value still kept constant to some extent, showing a good stability of chemical structure and electrophoresis display. Hereinto, the blue-white Cu-BTC-PEI/TiO 2 system with high CR values behaved with the best represented in display effect. By comparison, these colored PEI-reinforced MOF microparticles are superior to the other organic color pigments and inorganic particles, in response capability, charge-to-mass ratio, preparation method, production cost, and stability in color, particle and display. It is anticipated to provide an innovative and promising technical path for color electrophoresis display. Materials and methods Materials Copper (II) nitrate trihydrate (Cu(NO 3 ) 2 ·3H 2 O), cobalt (II) nitrate hexahydrate (Co(NO 3 ) 2 ·6H 2 O), nickel (II) nitrate hexahydrate (Ni(NO 3 ) 2 ·6H 2 O), iron(III) nitrate nonahydrate (Fe(NO 3 ) 3 ·9H 2 O), 1,3,5-benzenetricarboxylic acid (BTC), polyvinylpyrrolidone (PVP; mean molecular weight (M.W.): ~58,000 g/mol.), polyethyleneimine (PEI; M.W.: 1,800, 10,000, and 25,000 g/mol.), polyacrylic acid (PAA; M.W.: ~2,000 g/mol.), polyethylene glycol (PEG; M.W.: ~2000 g/mol.), sorbitan oleate (Span 80), anatase titanium dioxide (TiO 2 ; mean size: ~200 nm) naoparticles were purchased from Shanghai Macklin Biochemical Co.. Other reagents and organic solvents were of analytical grade, and directly used without further purification. Moreover, polyisobutenyl succinic anhydrides (PIBSA; industrial grade) as acidic charge control agent was provided by Jinzhou Gadorun Materials Technology Co., LTD. Isododecane was supplied by Weng Jiang Regent Co. Indium tin oxide (ITO) glass plates (thickness: 1.1 mm; area resistance: 30 Ω/mm 2 ; transmittance 550 nm: 85 ~ 87%) were bought from Wuhu Token Sciences Co., LTD (Wuhu, China), and completely rinsed and dried prior to use. Syntheses and characterizations of polymer-reinforced MOF microparticles The whole synthetic routes were systematically shown in Fig. 1 A, according to the previously reported solvothermal method 40 – 43 . Syntheses of colored MOF microparticles constructed by coordination of metal ion (M) and BTC (M-BTC; M = Cu, Fe, Ni, or Co) Cu-BTC: Typically, 5 mL of ethanol solution of PVP (10 g/L), 25 mL of dimethyl formamide (DMF), 25 mL of ethanol solution of BTC (0.10 M), and 25 mL of aqueous solution of Cu(NO 3 ) 2 ·3H 2 O (0.02 M), were added in turn every 10 minutes, and thoroughly stirred. Subsequently, the resulting mixture was poured into a stainless-steel vessel and then heated up in the oven (FED 56, Binder, Germany) at 80 ℃ for 24 hours. After cooling overnight, the product was washed with anhydrous ethanol (EtOH) three times by centrifugation, and dried in vacuum at 70°C to obtain a blue powder. Fe-BTC: Typically, 14.544 g of Fe(NO 3 ) 3 ·9H 2 O and 5.04 g of BTC were codissolved in 36 mL of deoxidized ultrapure water, and magnetically stirred at ambient temperature for 1 hour. Subsequently, the mixture was poured into a stainless-steel vessel and then heated up to 160°C in the oven (FED 56, Binder, Germany) for 12 hours. After cooling overnight, the solid products were collected by centrifugation, and then mixed with a right amount of ultrapure water and anhydrous ethanol at 70°C for 3 hours. Finally, the reddish-brown powders were obtained by centrifugation and vacuum drying at 60°C. Ni-BTC: Typically, 3 g of PVP, 0.3 g of BTC, 0.864 g of Ni(NO 3 ) 2 ·6H 2 O were added into the mixed solvent (H 2 O : ethanol : DMF = 20 mL : 20 mL : 20 mL) in turn, and magnetically stirred for 30 minutes. Subsequently, the resulting mixture was transferred to a 100 mL stainless-steel vessel, and heated up to 150°C in the oven (FED 56, Binder, Germany) for 10 hours. Finally, the green products were washed three times with methanol by centrifugation, and dried in vacuum at 60°C for 10 hours. Co-BTC: Typically, 1.2 g of Co(NO 3 ) 2 ·6H 2 O and 0.3 g of BTC were added into 30 mL of DMF in turn, and magnetically stirred for 0.5 hour. Subsequently, the mixed solution was transferred to a 50 mL stainless-steel vessel, and heated up to 120°C in the oven (FED 56, Binder, Germany) for 15 hours. Finally, the purple products were cooled, filtered, washed with DMF and ethanol, and dried in vacuum at 80°C overnight. Syntheses of colored polymer-modified MOF microparticles (M-BTC-polymer) PEI (M.W.: 1,800, 10,000, and 25,000 g/mol.), PAA (M.W.: 2,000 g/mol.), PEG (M.W.: 2,000 g/mol.) were ultrasonically dissolved in anhydrous ethanol with the settled concentration of 10 mg/mL, respectively. At the same time, M-BTC microparticles was dispersed in anhydrous ethanol with the settled concentration of 1.5 mg/mL. Subsequently, 250 µL of polymer solution was dropwise added into 8 mL of M-BTC dispersion, and then ultrasonicated for 15 minutes, following by magnetic stirring for 30 minutes. Next, the mixture was collected by centrifugation (8000 rpm, 10 minutes) and washed twice with anhydrous ethanol. The final product was obtained by vacuum drying overnight at 50 ℃. Prior to characterization, each sample was centrifuged and washed three times with anhydrous ethanol for full removal of the residual polymers. Here the resulting product was recorded as M-BTC-PEI (or PAA, PEG; 20%), respectively, according to the mass injection ratio of PEI (or PAA, PEG) to M-BTC (1:5). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) The microscopic morphologies of the resulting MOF microparticles were photographed by SEM (Ultra 55, Zeiss, Germany). The related elemental compositions were analyzed by EDS (Dual QUANTAX 200, Bruker, Germany) with a XFlash6 dual-probe (Bruker, Germany). All the samples were the ethanol dispersion solutions of the resulting MOF microparticles with the fixed concentration of 1 mg/mL. Each 10 µL of the sample dispersion was taken out on the silicon wafer till dried out, and then were sprayed with platinum particles (thickness: 15 nm). Transmission electron microscopy (TEM) The configurational morphologies of the resulting MOF microparticles were observed by TEM (JEM-1400 plus, JEOL, Japan). All the samples were also the ethanol dispersion solutions with the fixed MOF concentration of 1 mg/mL. Fourier transform infrared spectra (FT-IR) and attenuated total reflectance-Fourier transform infrared spectra (ATR-FTIR) The surface variations between the crude and modified MOF microparticles were characterized by FT-IR in the spectral range from 4000 to 400 cm − 1 with a resolution of 2 cm − 1 (Vertex 70, Bruker, Germany) using potassium bromide (KBr) tableting. The rich functional groups on the surfaces of the resulting MOF microparticles were further determined by ATR-FTIR in the spectral range from 4000 to 800 cm − 1 and the temperature range from 30 to 100 ℃. Thermogravimetric analyzer (TGA) The thermogravimetric analyses of the resulting MOF microparticles were performed using TGA (TGA2 Metler-Toledo, Switzerland). Each sample (~ 10 mg) was measured within a temperature range from 30 to 800°C with the settled heating rate of 10°C/minute, in oxygen flow with the fixed rate of 20 mL/minute. Ultrapurple-visible spectra (UV-Vis) The electrophoretic particles were characterized with a wavelength range from 300 to 500 nm using UV-Vis spectrophotometer (LAMBDA 950, Perkin-elmer, USA). Here the sample was the isododecane dispersion solution of the resulting MOF microparticles with a fixed concentration of 10 mg/mL. X-ray photoelectron spectra (XPS) The surface elemental compositions of the resulting MOF microparticles XPS spectra were determined by an X-ray photoelectron spectrometer (AXIS SUPRA, Shimadzu, Japan) equipped with monochromatic Al Kα (E = 1486.6 eV) radiation. The measured XPS energies were collected using the C1s peak of the C–C bond at 284.6 eV. Powder X-ray Diffraction (XRD) The crystal phase analyses of the resulting MOF microparticles were carried out at room temperature using X-ray diffractometer (D8 ADVANCE, Bruker, Germany) with a generator voltage of 40 kV and a 2 θ range of 5 ~ 70°. Here the scanning speed was set as 5°/minute. Dynamic light scattering (DLS) & Zeta potential analysis The colloidal properties of the resulting MOF microparticles were measured using a nanoparticle size & Zeta potential analyzer (NanoBrook 90 plus PALS, Brookhaven, U.S.A.). Here the sample was the isododecane dispersion solution of the resulting MOF microparticles with a fixed concentration of 0.02 mg/mL. Typically, the resulting autocorrelation functions were analyzed using built-in software to extract hydrodynamic dimensions and polydispersity (PDI). And the auto-balanced voltage values and default parameters was used to obtain the Zeta potential. Electrophoretic characterizations of polymer-reinforced MOF microparticles Preparation of colored electrophoretic inks based on polymer-reinforced MOF microparticles Typically, 0.1 g of the resulting M-BTC-PEI (M = Cu, Fe, Ni, Co) microparticle was ultrasonically dispersed into 1 mL of the isododecane solution of PIBSA (50 mg/mL) to obtain positively charged colored electrophoretic ink. Preparation of white electrophoretic ink Typically, 0.1 g of the modified TiO 2 nanoparticles was ultrasonically dispersed in 1 mL of the isododecane solution of PIBSA (50 mg/mL) to obtain positively charged white electrophoretic ink. Fabrication of two-color electrophoretic display cell Just as shown in Fig. 1 B, the adopted display cell comprised two parallel ITO glass plates (3 cm×3 cm) with the inner face-to-face ITO layers and the fixed spacing distance (100 µm) determined by a standard double-sided tape. As the electrophoretic fluid, 1 mL of the colored electrophoretic ink and 0.5 mL of the white electrophoretic ink were ultrasonically mixed to obtain the two-color electrophoretic ink, and then injected into the cell. Effect test of electrophoretic display During the process of electrophoretic display, a predetermined driving voltage of ± 20V was applied through a direct current (DC) power supply (CE0400010T, Earthworm Electronics, P. R. China). Here the display effect was evaluated by reflectance, response time, and color coordinates using a high-speed reflectometer (Admesy, Netherlands), according to CIE (Commission Internationale de I' Éclairage) color space standard. Declarations Acknowledgements This work was financially supported by the Program for Guangdong Innovative and Entrepreneurial Teams (No. 2019BT02C241), Guangdong Provincial Key Laboratory of Optical Information Materials and Technology (No. 2023B1212060065), MOE International Laboratory for Optical Information Technologies, Startup Foundation from SCNU, and the 111 Project. Author details Corresponding Author Hao Li - South China Normal University, Guangzhou, China; orcid.org/0000-0003-1744-1526; Phone: +86-20-39314813; Email: [email protected] ; Fax: +86-20-39314813. Guofu Zhou − South China Normal University, Guangzhou, China; orcid.org/0000-0003-1101-1947; Phone: +86-20-39314813; Email: [email protected] ; Fax: +86-20-39314813. Authors Jiamin Cheng − South China Normal University, Guangzhou, China Mian Qin − South China Normal University, Guangzhou, China Wenhao Wang − South China Normal University, Guangzhou, China Jingxing Zhang − South China Normal University, Guangzhou, China Yao Wang - South China Normal University, Guangzhou, China; orcid.org/0000-0002-0713-5018; Conflict of interest There are no conflicts to declare. References Ye, S., Hosono, N. & Uemura, T. Polymer‐Grafting from MOF Nanosheets for the Fabrication of Versatile 2D Materials. Adv. Funct. Mater. 34 , 2312265 (2023). Chen, J. et al. Recent progress in mixed rare earth metal-organic frameworks: From synthesis to application. Coord. Chem. Rev. 485 , 215121 (2023). Sundriyal, S. et al. Metal-organic frameworks and their composites as efficient electrodes for supercapacitor applications. Coord. Chem. Rev. 369 , 15-38 (2018). Oh, J. W. et al. Dual-light emitting 3D encryption with printable fluorescent-phosphorescent metal-organic frameworks. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6249755","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":435423509,"identity":"06025e24-1b71-4227-b212-7120a6183d70","order_by":0,"name":"Hao Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyklEQVRIiWNgGAWjYBACAwYGxgMJFXA+M1FaGA4knCFZC2MbKVrM2Q8fOPBw3jYG+fazxyQYKqwTG9jPHsCrxbInLeFA4rbbDAZn8tIkGM6kJzbw5CXgd9iBHAOIFgkeMwnGtsOJDRI8Bvi1nH8D1DLnNoP8DJCWf8RouQGypeE2A8MNkJYGorQ8SziQcOw2j8GZHGOLhGPpxm08OYQclnzw4Y+a23Ly7WcMb3yosZbtZz+DXwsM8IDJBCBmI0r9KBgFo2AUjAK8AAAjLEYd9YwG2gAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-1744-1526","institution":"South China Normal University","correspondingAuthor":true,"prefix":"","firstName":"Hao","middleName":"","lastName":"Li","suffix":""},{"id":435423510,"identity":"4c174261-d4e8-41dd-90cb-b962d4e78dbb","order_by":1,"name":"Jiamin Cheng","email":"","orcid":"","institution":"South China Normal University","correspondingAuthor":false,"prefix":"","firstName":"Jiamin","middleName":"","lastName":"Cheng","suffix":""},{"id":435423511,"identity":"a67c6c24-b6f9-4f07-bc22-534cf135564d","order_by":2,"name":"Mian Qin","email":"","orcid":"","institution":"South China Normal University","correspondingAuthor":false,"prefix":"","firstName":"Mian","middleName":"","lastName":"Qin","suffix":""},{"id":435423512,"identity":"091264ac-ffba-4c9c-8284-f1d609f5a4da","order_by":3,"name":"Wenhao Wang","email":"","orcid":"","institution":"South China Normal University","correspondingAuthor":false,"prefix":"","firstName":"Wenhao","middleName":"","lastName":"Wang","suffix":""},{"id":435423513,"identity":"9d32cd5b-5294-4cf1-a821-b269c1617306","order_by":4,"name":"Jingxing Zhang","email":"","orcid":"","institution":"South China Normal University","correspondingAuthor":false,"prefix":"","firstName":"Jingxing","middleName":"","lastName":"Zhang","suffix":""},{"id":435423514,"identity":"7bc2a509-9014-431c-b496-6c95ecfcb7a8","order_by":5,"name":"Yao Wang","email":"","orcid":"","institution":"South China Normal University","correspondingAuthor":false,"prefix":"","firstName":"Yao","middleName":"","lastName":"Wang","suffix":""},{"id":435423515,"identity":"9189c9e4-3d52-4a75-9af6-379696c05fd8","order_by":6,"name":"Guofu Zhou","email":"","orcid":"","institution":"South China Normal University","correspondingAuthor":false,"prefix":"","firstName":"Guofu","middleName":"","lastName":"Zhou","suffix":""}],"badges":[],"createdAt":"2025-03-18 06:05:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6249755/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6249755/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41377-025-02095-3","type":"published","date":"2026-02-24T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":80828805,"identity":"72643b62-29b6-4830-b2dc-40b924278496","added_by":"auto","created_at":"2025-04-17 13:40:59","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":359248,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagrams on the preparation routes of the colored PEI-reinforced MOF microparticles (A), and the fabrication process of the electrophoretic display cell (B).\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/f6d63d788c1384f33dd4aed4.jpeg"},{"id":80827645,"identity":"f1981cce-f87c-4dbd-be4c-5438d3bdd5f8","added_by":"auto","created_at":"2025-04-17 13:32:59","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":757715,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of the resulting Cu-BTC (A), Fe-BTC (C), Ni-BTC (E), and Co-BTC microparticles (G), and the corresponding PEI-reinforced Cu-BTC-PEI (B), Fe-BTC-PEI (D), Ni-BTC-PEI (F), and Co-BTC-PEI microparticles (H); elemental mappings of the resulting Cu-BTC (I) and Cu-BTC-PEI sample (J). Notes: PEI M.W., 10,000 g/mol; PEI feed ratio, 30 wt.%.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/667fcec6c50d3163cb319517.jpeg"},{"id":80827647,"identity":"8a3cfb65-19d1-45ec-af04-52eabd721cb4","added_by":"auto","created_at":"2025-04-17 13:33:00","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":366365,"visible":true,"origin":"","legend":"\u003cp\u003ePowder XRD patterns (A), FT-IR spectra (B), and ATR-FTIR spectra (100 ℃) of the resulting M-BTC and M-BTC-PEI microparticles (C-F); high-resolution XPS spectra (G) and the corresponding O 1s spectra of the resulting Cu-BTC and Cu-BTC-PEI microparticles (H). Notes: PEI M.W., 10,000 g/mol; PEI feed ratio, 30 wt.%.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/70c4c1692891227d735a72fc.jpeg"},{"id":80827649,"identity":"6d40e5cb-bba5-4a0c-8af1-8b707017546b","added_by":"auto","created_at":"2025-04-17 13:33:00","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":245995,"visible":true,"origin":"","legend":"\u003cp\u003eTGA curves of the resulting M-BTC and M-BTC-PEI microparticles in oxygen atmospheres: Cu-BTC and Cu-BTC-PEI (A), Fe-BTC and Fe-BTC-PEI (B), Ni-BTC and Ni-BTC-PEI (C), and Co-BTC and Co-BTC-PEI (D). Notes: PEI M.W., 10,000 g/mol; PEI feed ratio, 30 wt.%.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/cff072cffaf5536918b567d1.jpeg"},{"id":80828806,"identity":"d1046463-6b9a-4659-8072-5999741a5553","added_by":"auto","created_at":"2025-04-17 13:41:00","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":259446,"visible":true,"origin":"","legend":"\u003cp\u003eZeta potentials and electrophoretic mobilities of the crude M-BTC microparticles and the reinforced M-BTC-PEI microparticles with different molecular weights and feed ratios of PEI in isododecane: Cu-BTC and Cu-BTC-PEI (A), Fe-BTC and Fe-BTC-PEI (B), Ni-BTC and Ni-BTC-PEI (C), and Co-BTC and Co-BTC-PEI (D).\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/7eef87d844270513903f934e.jpeg"},{"id":80827652,"identity":"d3c056f8-7cf3-462b-9da8-71b526bac38e","added_by":"auto","created_at":"2025-04-17 13:33:00","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":346404,"visible":true,"origin":"","legend":"\u003cp\u003eReflectance curves (A) and color chromaticity diagrams of the M-BTC isododecane solution (M-BTC concentration: 100 mg/mL) encapsulated inside the electrophoretic display cell (B; the object figures of the used M-BTC microparticles at the top right); UV-Vis spectra of the Cu-BTC-PEI isododecane solution (Cu-BTC concentration: 10 mg/mL) with the settled PIBSA concentration of 50 mg/mL (C) and the one without any PIBSA (D), and corresponding object figures (E; left, containing PIBSA; right, no PIBSA). Notes: PEI M.W., 10,000 g/mol; PEI feed ratio, 30 wt.%.\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/9822bd3dbfbc57b9dce74dd9.jpeg"},{"id":80829044,"identity":"8142c359-aa4a-4f39-b1f5-c36cf1ba27a7","added_by":"auto","created_at":"2025-04-17 13:49:00","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":283152,"visible":true,"origin":"","legend":"\u003cp\u003eAlternating waveform design of the applied driving DC voltage (A; ±20 V); two-color device reflectance of the M-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e isododecane solutions (mass ratio of the resulting M-BTC-PEI microparticle to the modified TiO\u003csub\u003e2\u003c/sub\u003e nanoparticle, 2:1) with the settled PIBSA concentration of 50 mg/mL encapsulated inside the electrophoretic display cell (B~E). Notes: PEI M.W., 10,000 g/mol; PEI feed ratio, 30 wt.%.\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/f4a087707f37b79bbd29fd2e.jpeg"},{"id":80828809,"identity":"38747eea-bcf5-45ff-a649-bfb5c157f2c6","added_by":"auto","created_at":"2025-04-17 13:41:00","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":375202,"visible":true,"origin":"","legend":"\u003cp\u003eColor EPD tests of the two-color M-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e electrophoretic inks (mass ratio of the resulting M-BTC-PEI microparticle to the modified TiO\u003csub\u003e2\u003c/sub\u003e nanoparticle, 2:1; PIBSA concentration, 50 mg/mL) encapsulated inside the electrophoretic display cell at ±20 V for 20 seconds, and corresponding color coordinates: Cu-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e (A), Fe-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e (B), Ni-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e (C), and Co-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e (D). Notes: PEI M.W., 10,000 g/mol; PEI feed ratio, 30 wt.%.\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/82de1b7bac134d2b6f92cc84.jpeg"},{"id":103392091,"identity":"2b1e4b87-63e1-4e74-b5f0-aa9551650af7","added_by":"auto","created_at":"2026-02-25 08:08:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4437870,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/81aaeb1e-cd95-42be-bbe8-7b92cd2ea8f3.pdf"},{"id":80827651,"identity":"223aac00-27a1-411c-9280-627d8d5a12d0","added_by":"auto","created_at":"2025-04-17 13:33:00","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":2799439,"visible":true,"origin":"","legend":"Supporting Informantion 0318","description":"","filename":"SupportingInformantion0318.docx","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/41990c01c9ee72c4c2ef1ba2.docx"},{"id":80827654,"identity":"a945d101-1538-4186-8078-ca6ba851ca45","added_by":"auto","created_at":"2025-04-17 13:33:00","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":8287256,"visible":true,"origin":"","legend":"\u003cp\u003eVideo S1\u003c/p\u003e","description":"","filename":"VideoS1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/d0bfae949ce4514004baccf6.mp4"},{"id":80827658,"identity":"196b1ac7-190a-46c0-97e2-180408ec5fe0","added_by":"auto","created_at":"2025-04-17 13:33:00","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":7248593,"visible":true,"origin":"","legend":"\u003cp\u003eVideo S2\u003c/p\u003e","description":"","filename":"VideoS2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/fc678d4d498b537aeef3bd4e.mp4"},{"id":80828808,"identity":"1f349e1e-35b7-4b80-99c3-61ff614df951","added_by":"auto","created_at":"2025-04-17 13:41:00","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":10627976,"visible":true,"origin":"","legend":"Video S3","description":"","filename":"VideoS3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/bd1a12f20ac445d014b7685d.mp4"},{"id":80827670,"identity":"21f759d2-b154-4940-9bf1-39adfdc687cd","added_by":"auto","created_at":"2025-04-17 13:33:00","extension":"mp4","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":21051490,"visible":true,"origin":"","legend":"Video S4","description":"","filename":"VideoS4.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6249755/v1/fe63b35f179347625a0cb8a4.mp4"}],"financialInterests":"There is no conflict of interest","formattedTitle":"Colored Polymer-reinforced Metal-organic Framework Microparticles with High Charge-to-mass Ratio for Electrophoretic Display","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAs a promising type of porous crystalline hybrids, metal-organic frameworks (MOFs) are assembled by coordination between inorganic metal ions and organic ligands\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. By variation of the two key components enable MOFs to be infinitely devolved into diverse chemical and physical properties\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. So besides high specific surface area and porosity, MOFs feature both controllable structure and function, and have been widely used in the fields of catalysis, adsorption, separation, sensing, drug delivery and so on\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn particular, MOFs exhibit unique charge characteristics of inorganic-organic hybrids. The overall charge of the framework can be tuned with the oxidation state of metal ions within the ligand\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, ZIF-8, ZIF-67, MIL-101(Cr), and MOF-801 were proved to be positively charged\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. From the perspective of electrophoretic particle, MOFs have few natural advantages: (1) more options for organic functional groups to allow exquisite modification\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e; (2) good morphology controllability, including wide variation of sizes ranging from micrometer to nanometer scale, and structures changing from three to zero dimensional\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e; (3) low and adjustable density, for example, the proven density of HKUST-1 changing from 0.883, 1.07, to 2.8 g/cm\u003csup\u003e3,11, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. The third virtue is very beneficial for improving migration rate and multiparticle resolution\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. In addition, rich, vivid, and stable colors of MOFs provide more possibilities for fine patterning and color electrophoretic display (EPD). Undoubtedly, MOFs are much lighter and more colorful than other inorganic electrophoretic particles (e.g. metal ion-doping TiO\u003csub\u003e2\u003c/sub\u003e nanoparticle)\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, and much easier to be modified, and more stable in color than common organic ones (e.g. color dye/pigment particles)\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. But MOFs still need less aggregation, higher charge density, better stability and compatibility, to meet the requirements of high-performance display\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. In general, a good way is polymer modification on the MOF surface \u003cem\u003evia.\u003c/em\u003e covalent anchoring or physical adsorption\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn our work, 1,3,5-benzenetricarboxylic acid (BTC) as a common organic ligand was coordinated with Cu\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e, Ni\u003csup\u003e2+\u003c/sup\u003e, and Co\u003csup\u003e2+\u003c/sup\u003e ion by solvothermal method, to form the blue, reddish-brown, green, and purple MOF (M-BTC) microparticles (i.e., Cu-BTC, Fe-BTC, Ni-BTC and Co-BTC), respectively (see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). And these resulting M-BTC microparticles were further reinforced by physically adsorbed polyethyleneimine (PEI) for stronger electrophoretic performances. Here PEI with a high amine density is easily localized on the surface of MOF microparticle through electrostatic interaction and hydrogen bonding. It not only makes the MOF structure more stabilized, but also endows the MOF surface with abundant amino groups to improve charge density. In addition, isododecane, an oil phase with ultralow polarity was chosen as electrophoresis medium, to effectively avoid possible MOF decomposition/transformation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eAs a truly mainstream reflective paper-like display, EPD has some distinct advantages, e.g. quick response, bistable state, high reliability, wide viewing angle, and low cost and power consumption, but is greatly limited by color and video\u003csup\u003e\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Although it is technically easy to colorize EPD using color filters, it comes at the expense of display brightness and resolution, as well as device thickness\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. So EPD is still facing a huge challenge on high-performance colored electrophoretic particles.\u003c/p\u003e \u003cp\u003eWe first integrated light and colorful MOF microparticles and polyelectrolyte functionalization into charged colloid particles, to develop a novel colored- electrophoretic particle. These MOFs represent four metals widely used in MOF synthesis: Cu, Fe, Ni, Co. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e) demonstrated the morphology of M-BTC and M-BTC-PEI. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB, those crude Cu-BTC microparticles were regular octahedra with uniform size of about 700 nm, and those PEI-modified Cu-BTC-PEI microparticles presented in similar but adherent morphology. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD, the blank Fe-BTC microparticles took a large agglomerate look comprising many irregular polyhedrons with a size of about 100 nm, and did not change much after PEI modification. It can be seen from in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF that, those original Ni-BTC microparticles appeared in rough microsphere with an average size of about 2 \u0026micro;m, and those PEI-modified ones almost remained unchanged. By comparison, both the Co-BTC and the Co-BTC-PEI microparticles were nano/micron disordered nanosheets in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eG and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eH. Evidently, all the above-mentioned MOF microparticles were completely consistent with what has been previously reported. And there was almost no change in morphology before and after PEI modification, indicating that the adsorbed PEI chains were limited. This was also confirmed by the energy dispersive spectroscopy (EDS) of Cu-BTC \u0026amp; Cu-BTC-PEI (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eI and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eJ) and Ni-BTC \u0026amp; Ni-BTC-PEI (see \u003cb\u003eFigure S2\u003c/b\u003e). Hereinto, a slight increase in nitrogen content showed the successful PEI modification on these M-BTC microparticles.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe powder x-ray diffraction (XRD) patterns of the resulting M-BTC and M-BTC-PEI microparticles in the 2θ angle region at 5\u0026thinsp;~\u0026thinsp;70◦ were illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA. Apparently, all the diffractograms before and after PEI modification were almost identical and in good agreement with the results previously reported in the literature, showing good crystalline. These major diffraction peaks were listed as below: Cu-BTC, 6.8\u0026deg; (200), 9.5\u0026deg; (220), 11.63\u0026deg; (222), 13.53\u0026deg; (400), 14.7\u0026deg; (331), 15.03\u0026deg; (420), 16.47\u0026deg; (422), 17.52\u0026deg; (333), 19.11\u0026deg; (440), 20.26 \u0026deg; (600), 24.11\u0026deg; (711), 26.10\u0026deg; (553), 29.37\u0026deg; (662), and 35.3\u0026deg; (951); Fe-BTC, 7.1\u0026deg; (440), 10.3\u0026deg; (660), 11.07\u0026deg; (428) ,12.65\u0026deg; (1022), 14.3\u0026deg; (088),20.16\u0026deg;(4814), 24.1\u0026deg; (6618) and 27.78\u0026deg;(9321); Ni-BTC, 12.2\u0026deg; (2\u0026ndash;10), 15.33\u0026deg; (002), 18.0\u0026deg; (300), 20.9\u0026deg;, 22.32\u0026deg;, 23.88\u0026deg;, 26.13\u0026deg; (2\u0026ndash;13), and 27.9\u0026deg; (5\u0026ndash;10); Co-BTC, 2\u003cem\u003eθ\u003c/em\u003e value of 10.92\u0026deg; (200), 14.6\u0026deg; (001), 18.8\u0026deg; (111), 20.1\u0026deg; (021), 24.69\u0026deg; (13\u0026thinsp;\u0026minus;\u0026thinsp;1), 25.36\u0026deg; (42\u0026thinsp;\u0026minus;\u0026thinsp;1), 27.19\u0026deg; (20\u0026thinsp;\u0026minus;\u0026thinsp;2), 33.9\u0026deg; (62\u0026thinsp;\u0026minus;\u0026thinsp;1), 35.43◦ (440).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB exhibited the characteristic functional groups of different M-BTC and M-BTC-PEI composites. In these Fourier-transform infrared spectra (FT-IR), few similar peaks at 750, 1360\u0026thinsp;~\u0026thinsp;1450, and 1550\u0026thinsp;~\u0026thinsp;1670 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, were attributed to symmetric, asymmetric stretching vibrations of C\u0026thinsp;=\u0026thinsp;C, C-O, and C\u0026thinsp;=\u0026thinsp;O bonds in the BTC ligands, respectively. And the representative absorption peaks at 725, 615, 720, and 720 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e corresponded to the vibrational peaks of the intrinsic coordination bonds between oxygen atom (O) and metal ion (i.e., Cu\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e, Ni\u003csup\u003e2+\u003c/sup\u003e and Co\u003csup\u003e2+\u003c/sup\u003e). But significant difference before and after PEI modification cannot be found, which may be attributed to the absorption overlap of the amino groups (N-H; 3100\u0026thinsp;~\u0026thinsp;3500 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e) with the hydroxy groups (-OH) of residual alcohol or water (300\u0026thinsp;~\u0026thinsp;3500 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e). So we performed high-temperature tests using variable temperature attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), to eliminate possible interference from the residual. Just as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB\u0026thinsp;\u003cb\u003e~\u0026thinsp;3E\u003c/b\u003e, all the N-H peaks of the resulting M-BTC-PEI microparticles still emerged clearly in the range from 3100 to 3400 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, indicating successful PEI adsorption on the surface of M-BTC. In addition, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eG and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eH further exhibited the chemical states and compositions of Cu-BTC and Cu-BTC-PEI microparticles. Obviously, the C 1s, O 1s, and Cu 2p peak kept constant, and the N 1s peak was enhanced after PEI modification, indicating the successful bonding of PEI chains. Correspondingly, both the binding energies of the carbonyl group (C\u0026thinsp;=\u0026thinsp;O) and the carbon-oxygen bond (C-O) in BTC ligands also increased with 0.59 eV. This red shift may be attributed to the newly formed hydrogen bonds between oxygen atom and amino groups of PEI chain (N-H∙∙∙O).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe thermogravimetric (TGA) curves of the resulting M-BTC and M-BTC-PEI microparticles were recorded in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Apparently, all the M-BTC microparticles before and after PEI modification, behaved with almost the same residual masses but the different thermolytic behaviors. The first stage of weight loss below 150 ℃ undoubtedly originates from the removal of the residual solvent (e.g. water, ethanol, and DMF). The differences in thermolysis were mainly manifested in the subsequent process (see \u003cb\u003eFigure S3\u003c/b\u003e). It is well-known that, the decomposition range of the crude BTC molecules is normally between 300 and 350 ℃\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, and broadened to higher temperature after coordination with metal ions\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. This embodied well in the thermogravimetric curves of these M-BTC microparticles above 300 ℃. And the thermolysis of PEI also occurs in the temperature range between 300 and 350 ℃\u003csup\u003e\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Hence, in the main stage of weight loss between 150 and 500 ℃, those modified PEI chains visibly made M-BTC-PEI microparticles decomposed slightly faster than the crude M-BTC microparticles (see \u003cb\u003eFigure S3\u003c/b\u003e). Although the accurate mass of PEI in the M-BTC-PEI microparticles is very difficult to be determined, its existence can be confirmed.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOf course, the reinforcing effect of PEI modification is more reflected from the colloidal nature of the M-BTC-PEI microparticle. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and S4, all the Zeta potentials of the M-BTC microparticles were around 10 mV, which was caused by the exposed carboxyl groups on the MOF surface. To M-BTC-PEI microparticles, the abundant protonated amino groups of the linked PEI chains inevitably enabled these microparticles to convert into being positively charged. At the same PEI feed of 20 wt.%, different molecular weights of PEI brought about different Zeta potential. Hereinto, PEI with the molecular weight of 10,000 g/mol was viewed as the best option, whose corresponding Zeta potential was slightly higher than the ones\u0026rsquo; with the molecular weight of 25,000 g/mol. It seems that, larger random coil of the latter may be unfavorable for PEI bonding and adsorption. As the molecular weights of PEI was settled as 10, 000 g/mol, all the maximum Zeta potential of the M-BTC-PEI microparticles emerged around +\u0026thinsp;30 mV at the same PEI feed of 30 wt.%. Similarly, higher feed above the saturated bonding point may be not helpful for improving surface potential. Meanwhile, such variation in Zeta potential also appeared in mobility (see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). So the optimized parameters of PEI modification for those electrophoretic M-BTC-PEI microparticles were chosen as: the molecular weight of PEI was 10,000 g/mol, and the feed of PEI was 30 wt.%. Naturally, this surface PEI decoration consequentially made these M-BTC microparticles bigger with wider size distribution, just shown in \u003cb\u003eFigure S5\u003c/b\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eIn addition, we attempted to utilize negatively charged polyacrylic acid (PAA) and uncharged polyethylene glycol (PEG) to modify the surface of the M-BTC microparticles using the same non-covalent bonding. As shown in \u003cb\u003eFigure S6\u003c/b\u003e, plentiful carboxyl groups of the bonded PAA chains further rendered those resulting M-BTC-PAA microparticles more negatively charged to about \u0026minus;\u0026thinsp;30 mV. Similarly, plentiful hydroxyl groups of the bonded PEG chains only leaded to a slight decrement of the Zeta potential of those resulting M-BTC-PEG microparticles. It is a sign that, this non-covalent \u0026ldquo;adsorption\u0026rdquo; (e.g. hydrogen bonding and electrostatic interaction) is suitable for various polymers, and applicable for adjusting the charge properties of the MOF surface.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParticle characteristics of blank PEI chains, M-BTC and M-BTC-PEI microparticles in isododecane.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eZeta potential (mV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMobility\u003c/p\u003e \u003cp\u003e(\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003em\u003csup\u003e2\u003c/sup\u003e/Vs)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eEffective Size\u003c/p\u003e \u003cp\u003e(nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePolydispersity\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePEI 1800\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e10.31\u0026thinsp;\u0026plusmn;\u0026thinsp;1.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.014\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.525\u0026thinsp;\u0026plusmn;\u0026thinsp;0.086\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePEI 1W\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e13.51\u0026thinsp;\u0026plusmn;\u0026thinsp;1.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e-0.018\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e9.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.225\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePEI 2.5W\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e15.41\u0026thinsp;\u0026plusmn;\u0026thinsp;1.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e9.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.221\u0026thinsp;\u0026plusmn;\u0026thinsp;0.024\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCu-BTC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e-14.89\u0026thinsp;\u0026plusmn;\u0026thinsp;1.026\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e-0.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e738.36\u0026thinsp;\u0026plusmn;\u0026thinsp;9.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.265\u0026thinsp;\u0026plusmn;\u0026thinsp;0.025\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCu-BTC-PEI 30%\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e27.51\u0026thinsp;\u0026plusmn;\u0026thinsp;1.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.036\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e782.44\u0026thinsp;\u0026plusmn;\u0026thinsp;12.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.2815\u0026thinsp;\u0026plusmn;\u0026thinsp;0.031\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFe-BTC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e-9.50\u0026thinsp;\u0026plusmn;\u0026thinsp;1.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e-0.010\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e734.84\u0026thinsp;\u0026plusmn;\u0026thinsp;6.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.268\u0026thinsp;\u0026plusmn;\u0026thinsp;0.026\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFe-BTC-PEI 30%\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e30.57\u0026thinsp;\u0026plusmn;\u0026thinsp;2.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.041\u0026thinsp;\u0026plusmn;\u0026thinsp;0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e806.87\u0026thinsp;\u0026plusmn;\u0026thinsp;13.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.330\u0026thinsp;\u0026plusmn;\u0026thinsp;0.034\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNi-BTC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e-13.08\u0026thinsp;\u0026plusmn;\u0026thinsp;1.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e-0.016\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1890.94\u0026thinsp;\u0026plusmn;\u0026thinsp;29.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.351\u0026thinsp;\u0026plusmn;\u0026thinsp;0.021\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNi-BTC-PEI 30%\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e36.11\u0026thinsp;\u0026plusmn;\u0026thinsp;2.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.047\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2018.78\u0026thinsp;\u0026plusmn;\u0026thinsp;74.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.385\u0026thinsp;\u0026plusmn;\u0026thinsp;0.067\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCo-BTC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e-3.91\u0026thinsp;\u0026plusmn;\u0026thinsp;1.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e-0.009\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1270.70\u0026thinsp;\u0026plusmn;\u0026thinsp;10.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.296\u0026thinsp;\u0026plusmn;\u0026thinsp;0.031\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCo-BTC-PEI 30%\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e35.54\u0026thinsp;\u0026plusmn;\u0026thinsp;1.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.047\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1307.40\u0026thinsp;\u0026plusmn;\u0026thinsp;22.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.321\u0026thinsp;\u0026plusmn;\u0026thinsp;0.013\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cb\u003eNote\u003c/b\u003e: In M-BTC-PEI 30%, PEI denoted the bonded PEI chain with the molecular weight of 10,000 g/mol, and 30% did the feed ratio of PEI.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSubsequently, these PEI-reinforced MOF microparticles were dispersed with an acidic charge control agent (polyisobutenyl succinic anhydrides, PIBSA) into isododecane to formulate a series of colored electrophoretic inks. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA showed that, all the reflectance spectra of the M-BTC-PEI inks agreed well with the real colors of the M-BTC-PEI microparticles. We further calculated their tristimulus values (i.e., \u003cem\u003eX\u003c/em\u003e, \u003cem\u003eY\u003c/em\u003e, and \u003cem\u003eZ\u003c/em\u003e) according to the following formula (Eq.\u0026nbsp;1\u0026thinsp;\u003cb\u003e~\u0026thinsp;5\u003c/b\u003e) and converted into chrominance coordinates.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}X=\\kappa\\:\\sum\\:_{\\lambda\\:}{{\\phi\\:}}_{{\\lambda\\:}}\\left({\\lambda\\:}\\right)\\stackrel{-}{{\\chi\\:}}\\left({\\lambda\\:}\\right)\\varDelta\\:\\lambda\\:\\#\\left(\\text{E}\\text{q}\\text{u}\\text{a}\\text{t}\\text{i}\\text{o}\\text{n}\\:1\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}Y=\\kappa\\:\\sum\\:_{\\lambda\\:}{{\\phi\\:}}_{{\\lambda\\:}}\\left({\\lambda\\:}\\right)\\stackrel{-}{\\mathcal{Y}}\\left({\\lambda\\:}\\right)\\varDelta\\:\\lambda\\:\\#\\left(\\text{E}\\text{q}\\text{u}\\text{a}\\text{t}\\text{i}\\text{o}\\text{n}\\:2\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}Z=\\kappa\\:\\sum\\:_{\\lambda\\:}{{\\phi\\:}}_{{\\lambda\\:}}\\left({\\lambda\\:}\\right)\\stackrel{-}{\\mathcal{Z}}\\left({\\lambda\\:}\\right)\\varDelta\\:\\lambda\\:\\#\\left(\\text{E}\\text{q}\\text{u}\\text{a}\\text{t}\\text{i}\\text{o}\\text{n}\\:3\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\kappa\\:=\\frac{100}{\\sum\\:_{\\lambda\\:}\\text{S}\\left({\\lambda\\:}\\right)\\stackrel{-}{\\mathcal{Y}}\\left({\\lambda\\:}\\right){\\Delta\\:}{\\lambda\\:}}\\#\\left(\\text{E}\\text{q}\\text{u}\\text{a}\\text{t}\\text{i}\\text{o}\\text{n}\\:4\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Eque\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Eque\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\phi\\:\\left({\\lambda\\:}\\right)=R\\left({\\lambda\\:}\\right)S\\left({\\lambda\\:}\\right)\\#\\left(\\text{E}\\text{q}\\text{u}\\text{a}\\text{t}\\text{i}\\text{o}\\text{n}\\:5\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003ek\u003c/em\u003e is the normalization constant, \u003cem\u003eΔλ\u003c/em\u003e is the wavelength interval (1 nm), \u003cem\u003eS(λ)\u003c/em\u003e is the relative spectral distribution of the light source (D65), \u003cem\u003eR(λ)\u003c/em\u003e is the reflectance of the sample under this light source, \u003cem\u003eφ(λ)\u003c/em\u003e and \u003cem\u003eφ\u003c/em\u003e\u003csub\u003e\u003cem\u003eλ\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(λ)\u003c/em\u003e are the relative color stimulus function and the color stimulus function, respectively, and \u003cem\u003eφ(λ)\u003c/em\u003e can be used instead of \u003cem\u003eφ\u003c/em\u003e\u003csub\u003e\u003cem\u003eλ\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(λ)\u003c/em\u003e for the reflected object color. So, we calculated out \u003cem\u003ek\u003c/em\u003e and \u003cem\u003eXYZ\u003c/em\u003e based on the standard value of \u003cem\u003eS(λ)\u003c/em\u003e and the measured \u003cem\u003eR(λ)\u003c/em\u003e, and obtained the color matching functions of the CIE 1931 standard chromaticity observer (i.e., \u003cem\u003ex\u003c/em\u003e, \u003cem\u003ey\u003c/em\u003e, and \u003cem\u003ez\u003c/em\u003e) by the corresponding formula, \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eX\u003c/em\u003e/\u003cem\u003eX\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eY\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eZ\u003c/em\u003e, \u003cem\u003ey\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eY\u003c/em\u003e/X\u0026thinsp;+\u0026thinsp;\u003cem\u003eY\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eZ\u003c/em\u003e, and \u003cem\u003ez\u003c/em\u003e\u0026thinsp;=\u0026thinsp;Z/\u003cem\u003eX\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eY\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eZ\u003c/em\u003e. All the results, including the detailed CIE coordinate parameters, were finally plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB, which also corresponds well to the real colors of the M-BTC-PEI microparticles.\u003c/p\u003e \u003cp\u003eGiven many polar groups on the surface of the M-BTC-PEI microparticles, a right amount of PIBSA as both dispersant and charge control agent, was added into nonpolar isododecane dispersion against possible aggregation. In particular, the long and flexible carbon chain of PIBSA has a spatial site-blocking effect to keep these electrophoretic microparticles away from each other. Just shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC and \u003cb\u003eD\u003c/b\u003e, the ultraviolet-visible spectra (UV-Vis) absorbance of the Cu-BTC-PEI dispersion decreased slowly within 1 hour in an assisting effect of PIBSA, but the one without PIBSA cannot keep in a good dispersion even in 5 minutes. In this Cu-BTC-PEI/PIBSA formula, those colloid particles clearly exhibited good dispersibility in isododecane, especially low apparent density close to that of isododecane. This is also reflected in the corresponding object figures (see Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eE).\u003c/p\u003e \u003cp\u003eNext, we verified the single particle electrophoresis system of M-BTC-PEI microparticles in PIBSA/isododecane for the first time. At a driving direct current (DC) voltage of 20 V, those M-BTC-PEI microparticles were visibly fixed on the side of the negative ITO electrode, and the other part became completely transparent while the electrophoresis plate tilted (see \u003cb\u003eFigure S7\u003c/b\u003e). Apparently, these electrophoretic microparticles were positively charged. And we integrated the modified TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles as representative white electrophoretic particles into this dispersion, to form a two-color electrophoretic ink. As shown in \u003cb\u003eFigure S8\u003c/b\u003e and \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e, the applied TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles had few basic features: particle size, ~\u0026thinsp;200 nm; Zeta potential, + 55.57 mV; electrophoretic mobility, 4.1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e m\u003csup\u003e2\u003c/sup\u003e/(Vs). Here the Zeta potential is higher than that of the M-BTC-PEI microparticles, and surely make electrophoresis migration of the modified TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles faster under the same driving situation. It may be effective to avoid possible adsorption, agglomeration, and precipitation of positive and negative particles during multiple electrophoresis to some extent.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThis two-color electrophoretic ink was poured into electrophoretic display cell, and then driven at an alternating DC voltage of \u0026plusmn;\u0026thinsp;20 V (see Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eA) in daylight. Hereinto, response time (\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eon\u003c/em\u003e\u003c/sub\u003e) and shutdown time of electrophoretic display (\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eoff\u003c/em\u003e\u003c/sub\u003e; also known as recovery time) were defined as the required time from baseline to 90% of reflectance maximum, and the one from 90% of reflectance maximum to baseline, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eB\u0026thinsp;\u003cb\u003e~\u0026thinsp;E\u003c/b\u003e showed that, all the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eon\u003c/em\u003e\u003c/sub\u003e of the M-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e inks were less than 2.3 seconds, and all the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eoff\u003c/em\u003e\u003c/sub\u003e were less than 5.9 seconds under the low field strength of 0.02 V/\u0026micro;m. Here high charge-to-mass ratio of the M-BTC-PEI microparticles based on high Zeta potential and low apparent density is the main reason of rapid response. Verly clearly, the Co-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e formula was the most effective: \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eon\u003c/em\u003e\u003c/sub\u003e, 1.10 seconds; \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eoff\u003c/em\u003e\u003c/sub\u003e, 4.82 seconds. Because Co-BTC-PEI microparticle took the lead in charge density per unit volume and mobility: Zeta potential, 35.54\u0026thinsp;\u0026plusmn;\u0026thinsp;1.69 mV; effective size, 1307.40\u0026thinsp;\u0026plusmn;\u0026thinsp;22.40 nm; mobility, 4.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003em\u003csup\u003e2\u003c/sup\u003e/Vs. In particular, both the reflectivity and the response speed were independent of the repetitive switching, indicating the good stability of this electrophoresis system.\u003c/p\u003e \u003cp\u003eAs well-known, contrast ratio (\u003cem\u003eCR\u003c/em\u003e) is the ratio of the white reflectance value (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ew\u003c/em\u003e\u003c/sub\u003e) to the black reflectance value (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sub\u003e), namely \u003cem\u003eCR\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ew\u003c/em\u003e\u003c/sub\u003e/\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sub\u003e. In this study, the \u003cem\u003eCR\u003c/em\u003e value is defined as the ratio of \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ew\u003c/em\u003e\u003c/sub\u003e to the color reflectance value, and named as \u003cem\u003eCR\u003c/em\u003e\u003csub\u003e\u003cem\u003eCu\u0026minus;T\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eCR\u003c/em\u003e\u003csub\u003e\u003cem\u003eFe\u0026minus;T\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eCR\u003c/em\u003e\u003csub\u003e\u003cem\u003eNi\u0026minus;T\u003c/em\u003e\u003c/sub\u003e, and \u003cem\u003eCR\u003c/em\u003e\u003csub\u003e\u003cem\u003eCo\u0026minus;T\u003c/em\u003e\u003c/sub\u003e according to the corresponding M-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e ink, respectively. It was drawn from Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eB\u0026thinsp;\u003cb\u003e~\u0026thinsp;E\u003c/b\u003e that, \u003cem\u003eCR\u003c/em\u003e\u003csub\u003e\u003cem\u003eFe\u0026minus;T\u003c/em\u003e\u003c/sub\u003e (1.37)\u0026thinsp;\u0026gt;\u0026thinsp;\u003cem\u003eCR\u003c/em\u003e\u003csub\u003e\u003cem\u003eCu\u0026minus;T\u003c/em\u003e\u003c/sub\u003e (1.35)\u0026thinsp;\u0026gt;\u0026thinsp;\u003cem\u003eCR\u003c/em\u003e\u003csub\u003e\u003cem\u003eNi\u0026minus;T\u003c/em\u003e\u003c/sub\u003e (1.23)\u0026thinsp;\u0026gt;\u0026thinsp;\u003cem\u003eCR\u003c/em\u003e\u003csub\u003e\u003cem\u003eCo\u0026minus;T\u003c/em\u003e\u003c/sub\u003e (1.16). By the comprehensive comparison of the four key parameters, i.e. \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eon\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eoff\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eCR\u003c/em\u003e, and color, the Cu-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e ink was viewed as the best option, while the Co-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e ink had the fastest response but the lowest \u003cem\u003eCR\u003c/em\u003e value.\u003c/p\u003e \u003cp\u003eIn actual electrophoresis scenes, the real-time variations in chromaticity values of the M-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e inks were monitored using a colorimeter. As we can see from Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, \u003cb\u003eVideo S1\u003c/b\u003e, \u003cb\u003eS2\u003c/b\u003e, \u003cb\u003eS3\u003c/b\u003e, and \u003cb\u003eS4\u003c/b\u003e, the blue-white Cu-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e and the reddish-brown -white Fe-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e systems with high \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ew\u003c/em\u003e\u003c/sub\u003e values were undoubtedly the best represented in display effect. First, the two-color coordinates were far away from the white point (0.33, 0.33). Second, both the Cu-BTC-PEI and Fe-BTC-PEI microparticles showed significantly behaved better with small size, regular morphology, and high color saturation (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Third, both of them had high charge density per unit volume and mobility in the core electrophoretic index (see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). By comparison, the purple-white Co-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e system did not perform well, which is mainly ascribed to its large size and irregular morphology\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMoreover, we collected and characterized those charged M-BTC-PEI microparticles on the electrophoretic plate after continuous power over 1 hour. In \u003cb\u003eFigure S9\u003c/b\u003e, the characteristic peaks of those MOF microparticles still remained, indicating the good structural stability after multiple electrophoresis in low dielectric liquid. And we also tested the four two-color M-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e electrophoretic systems after multiple driving cycles with a duration of 500 seconds were applied. \u003cb\u003eFigure S10\u003c/b\u003e exhibited that, both the Cu-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e and Fe-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e systems played with great consistency in reflectance. Only a slight decrement in reflectance and \u003cem\u003eCR\u003c/em\u003e value appeared at the later cycles. It may result from possible aggregation of white TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles with the colored M-BTC-PEI microparticles.\u003c/p\u003e \u003cp\u003eCompared with the other color electrophoretic particles, these PEI-reinforced MOF microparticle that we first have distinct advantages in driving field strength and response time, just shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. And their low cost, facile preparation, high and high stability in color, particle and display, are also obviously superior to the other organic color pigments and inorganic particles.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of the electrophoretic characteristics of the reported color electrophoretic inks.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterials\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eZeta potential (mV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eElectrophoretic mobility\u003c/p\u003e \u003cp\u003e(10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e m\u003csup\u003e2\u003c/sup\u003e/V\u0026middot;s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAverage diameter (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDriving Voltage (V) / Spacing (\u0026micro;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eon\u003c/em\u003e\u003c/sub\u003e (s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eReference\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFe/Co/Al-doped TiO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026minus;102.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;0.1048\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e286.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30 V/~\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.121\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCuPcCl\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-26.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\\\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30 V/1000 \u0026micro;m\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePY110/PS\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003ePY118/PE\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-60~-70\u003c/p\u003e \u003cp\u003e-30-40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\\\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e500\u003c/p\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15 V/1000 \u0026micro;m\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBAM-MPS-PLMA\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026minus;63.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\\\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30 V/~\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eRYB-poly(styrene-co-4-VP)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-2.89\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20 V/100 \u0026micro;m\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\\\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePY13-\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003ePR254\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003ePB15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-3.45\u003c/p\u003e \u003cp\u003e-31.83\u003c/p\u003e \u003cp\u003e-0.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-8.269\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e-7.631\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e-1.076\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e217.7\u003c/p\u003e \u003cp\u003e155.2\u003c/p\u003e \u003cp\u003e80.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100 V/1000 \u0026micro;m\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1s\u003c/p\u003e \u003cp\u003e0.8s\u003c/p\u003e \u003cp\u003e0.5s\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTiO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e-OTS/P(4-VP-co-LA21)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-3.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-2.5\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e435\u0026thinsp;\u0026plusmn;\u0026thinsp;16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e50 V/100 \u0026micro;m\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.416\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePB-IL235\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e+\u0026thinsp;71.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e+\u0026thinsp;1.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e263\u0026thinsp;~\u0026thinsp;438\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\\\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\\\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFe\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e4\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e@SiO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-55.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\\\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e101\u0026thinsp;~\u0026thinsp;177\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.5 V/50 \u0026micro;m\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.472\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePIL/SCAs\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e+\u0026thinsp;4.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e+\u0026thinsp;6.17\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e188\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20 V/~\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.165\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCu-BTC-PEI\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eFe-BTC-PEI\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eNi-BTC-PEI\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eCo-BTC-PEI\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e+\u0026thinsp;27.51\u003c/p\u003e \u003cp\u003e+\u0026thinsp;30.57\u003c/p\u003e \u003cp\u003e+\u0026thinsp;36.11\u003c/p\u003e \u003cp\u003e+\u0026thinsp;35.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e+\u0026thinsp;3.6\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e+\u0026thinsp;4.1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e+\u0026thinsp;4.7\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e+\u0026thinsp;4.7\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e782.44, 806.87, 2018.78, 1327.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20 V/1000 \u0026micro;m\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.16\u003c/p\u003e \u003cp\u003e1.14\u003c/p\u003e \u003cp\u003e2.28\u003c/p\u003e \u003cp\u003e1.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eThis work\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003e\u003cb\u003eNote\u003c/b\u003e: To M-BTC-PEI, PEI was the bonded PEI chains with the molecular weight of 10,000 g/mol, and the feed ratio of 30 wt.%.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, we integrated the four colored MOF microparticles and polyelectrolytes into the blue, reddish-brown, green, and purple electrophoretic particles for the first time. In particular, the surface modification of PEI chains based on non-covalent interaction rendered these M-BTC microparticles reinforced fully: the Zeta potential rose from ~-10 to ~\u0026thinsp;+\u0026thinsp;30 mV; the electrophoretic mobility grew up from ~\u0026thinsp;1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e to over 3.6\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e m\u003csup\u003e2\u003c/sup\u003e/V\u0026middot;s. The colored M-BTC-PEI microparticles further paired with the representative white TiO\u003csub\u003e2\u003c/sub\u003e nanoparticle to form the two-color stable dispersions in nonpolar PIBSA/isododecane as the electrophoretic inks. Under the ultralow field strength of 0.02 V/\u0026micro;m, all the response time and recovery time were no more than 2.3 and 5.9 seconds, respectively. Even after long-time or multiple driving, these MOF microparticles and their reflectance value still kept constant to some extent, showing a good stability of chemical structure and electrophoresis display. Hereinto, the blue-white Cu-BTC-PEI/TiO\u003csub\u003e2\u003c/sub\u003e system with high \u003cem\u003eCR\u003c/em\u003e values behaved with the best represented in display effect. By comparison, these colored PEI-reinforced MOF microparticles are superior to the other organic color pigments and inorganic particles, in response capability, charge-to-mass ratio, preparation method, production cost, and stability in color, particle and display. It is anticipated to provide an innovative and promising technical path for color electrophoresis display.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eCopper (II) nitrate trihydrate (Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO), cobalt (II) nitrate hexahydrate (Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), nickel (II) nitrate hexahydrate (Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), iron(III) nitrate nonahydrate (Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO), 1,3,5-benzenetricarboxylic acid (BTC), polyvinylpyrrolidone (PVP; mean molecular weight (M.W.): ~58,000 g/mol.), polyethyleneimine (PEI; M.W.: 1,800, 10,000, and 25,000 g/mol.), polyacrylic acid (PAA; M.W.: ~2,000 g/mol.), polyethylene glycol (PEG; M.W.: ~2000 g/mol.), sorbitan oleate (Span 80), anatase titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e; mean size: ~200 nm) naoparticles were purchased from Shanghai Macklin Biochemical Co.. Other reagents and organic solvents were of analytical grade, and directly used without further purification.\u003c/p\u003e \u003cp\u003eMoreover, polyisobutenyl succinic anhydrides (PIBSA; industrial grade) as acidic charge control agent was provided by Jinzhou Gadorun Materials Technology Co., LTD. Isododecane was supplied by Weng Jiang Regent Co. Indium tin oxide (ITO) glass plates (thickness: 1.1 mm; area resistance: 30 Ω/mm\u003csup\u003e2\u003c/sup\u003e; transmittance 550 nm: 85\u0026thinsp;~\u0026thinsp;87%) were bought from Wuhu Token Sciences Co., LTD (Wuhu, China), and completely rinsed and dried prior to use.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSyntheses and characterizations of polymer-reinforced MOF microparticles\u003c/h3\u003e\n\u003cp\u003eThe whole synthetic routes were systematically shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA, according to the previously reported solvothermal method\u003csup\u003e\u003cspan additionalcitationids=\"CR41 CR42\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSyntheses of colored MOF microparticles constructed by coordination of metal ion (M) and BTC (M-BTC; M\u0026thinsp;=\u0026thinsp;Cu, Fe, Ni, or Co)\u003c/b\u003e \u003c/p\u003e \u003cp\u003eCu-BTC: Typically, 5 mL of ethanol solution of PVP (10 g/L), 25 mL of dimethyl formamide (DMF), 25 mL of ethanol solution of BTC (0.10 M), and 25 mL of aqueous solution of Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO (0.02 M), were added in turn every 10 minutes, and thoroughly stirred. Subsequently, the resulting mixture was poured into a stainless-steel vessel and then heated up in the oven (FED 56, Binder, Germany) at 80 ℃ for 24 hours. After cooling overnight, the product was washed with anhydrous ethanol (EtOH) three times by centrifugation, and dried in vacuum at 70\u0026deg;C to obtain a blue powder.\u003c/p\u003e \u003cp\u003eFe-BTC: Typically, 14.544 g of Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO and 5.04 g of BTC were codissolved in 36 mL of deoxidized ultrapure water, and magnetically stirred at ambient temperature for 1 hour. Subsequently, the mixture was poured into a stainless-steel vessel and then heated up to 160\u0026deg;C in the oven (FED 56, Binder, Germany) for 12 hours. After cooling overnight, the solid products were collected by centrifugation, and then mixed with a right amount of ultrapure water and anhydrous ethanol at 70\u0026deg;C for 3 hours. Finally, the reddish-brown powders were obtained by centrifugation and vacuum drying at 60\u0026deg;C.\u003c/p\u003e \u003cp\u003eNi-BTC: Typically, 3 g of PVP, 0.3 g of BTC, 0.864 g of Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO were added into the mixed solvent (H\u003csub\u003e2\u003c/sub\u003eO : ethanol : DMF\u0026thinsp;=\u0026thinsp;20 mL : 20 mL : 20 mL) in turn, and magnetically stirred for 30 minutes. Subsequently, the resulting mixture was transferred to a 100 mL stainless-steel vessel, and heated up to 150\u0026deg;C in the oven (FED 56, Binder, Germany) for 10 hours. Finally, the green products were washed three times with methanol by centrifugation, and dried in vacuum at 60\u0026deg;C for 10 hours.\u003c/p\u003e \u003cp\u003eCo-BTC: Typically, 1.2 g of Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO and 0.3 g of BTC were added into 30 mL of DMF in turn, and magnetically stirred for 0.5 hour. Subsequently, the mixed solution was transferred to a 50 mL stainless-steel vessel, and heated up to 120\u0026deg;C in the oven (FED 56, Binder, Germany) for 15 hours. Finally, the purple products were cooled, filtered, washed with DMF and ethanol, and dried in vacuum at 80\u0026deg;C overnight.\u003c/p\u003e\n\u003ch3\u003eSyntheses of colored polymer-modified MOF microparticles (M-BTC-polymer)\u003c/h3\u003e\n\u003cp\u003ePEI (M.W.: 1,800, 10,000, and 25,000 g/mol.), PAA (M.W.: 2,000 g/mol.), PEG (M.W.: 2,000 g/mol.) were ultrasonically dissolved in anhydrous ethanol with the settled concentration of 10 mg/mL, respectively. At the same time, M-BTC microparticles was dispersed in anhydrous ethanol with the settled concentration of 1.5 mg/mL. Subsequently, 250 \u0026micro;L of polymer solution was dropwise added into 8 mL of M-BTC dispersion, and then ultrasonicated for 15 minutes, following by magnetic stirring for 30 minutes. Next, the mixture was collected by centrifugation (8000 rpm, 10 minutes) and washed twice with anhydrous ethanol. The final product was obtained by vacuum drying overnight at 50 ℃. Prior to characterization, each sample was centrifuged and washed three times with anhydrous ethanol for full removal of the residual polymers. Here the resulting product was recorded as M-BTC-PEI (or PAA, PEG; 20%), respectively, according to the mass injection ratio of PEI (or PAA, PEG) to M-BTC (1:5).\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eScanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS)\u003c/h2\u003e \u003cp\u003eThe microscopic morphologies of the resulting MOF microparticles were photographed by SEM (Ultra 55, Zeiss, Germany). The related elemental compositions were analyzed by EDS (Dual QUANTAX 200, Bruker, Germany) with a XFlash6 dual-probe (Bruker, Germany). All the samples were the ethanol dispersion solutions of the resulting MOF microparticles with the fixed concentration of 1 mg/mL. Each 10 \u0026micro;L of the sample dispersion was taken out on the silicon wafer till dried out, and then were sprayed with platinum particles (thickness: 15 nm).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eTransmission electron microscopy (TEM)\u003c/h3\u003e\n\u003cp\u003eThe configurational morphologies of the resulting MOF microparticles were observed by TEM (JEM-1400 plus, JEOL, Japan). All the samples were also the ethanol dispersion solutions with the fixed MOF concentration of 1 mg/mL.\u003c/p\u003e\n\u003ch3\u003e\u003c/h3\u003e\n\u003cdiv class=\"Heading\"\u003e\u003cb\u003eFourier transform infrared spectra (FT-IR) and attenuated total reflectance-Fourier transform infrared spectra (ATR-FTIR)\u003c/b\u003e\u003c/div\u003e \u003cp\u003eThe surface variations between the crude and modified MOF microparticles were characterized by FT-IR in the spectral range from 4000 to 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a resolution of 2 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Vertex 70, Bruker, Germany) using potassium bromide (KBr) tableting. The rich functional groups on the surfaces of the resulting MOF microparticles were further determined by ATR-FTIR in the spectral range from 4000 to 800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the temperature range from 30 to 100 ℃.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eThermogravimetric analyzer (TGA)\u003c/h2\u003e \u003cp\u003eThe thermogravimetric analyses of the resulting MOF microparticles were performed using TGA (TGA2 Metler-Toledo, Switzerland). Each sample (~\u0026thinsp;10 mg) was measured within a temperature range from 30 to 800\u0026deg;C with the settled heating rate of 10\u0026deg;C/minute, in oxygen flow with the fixed rate of 20 mL/minute.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eUltrapurple-visible spectra (UV-Vis)\u003c/h2\u003e \u003cp\u003eThe electrophoretic particles were characterized with a wavelength range from 300 to 500 nm using UV-Vis spectrophotometer (LAMBDA 950, Perkin-elmer, USA). Here the sample was the isododecane dispersion solution of the resulting MOF microparticles with a fixed concentration of 10 mg/mL.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eX-ray photoelectron spectra (XPS)\u003c/h2\u003e \u003cp\u003eThe surface elemental compositions of the resulting MOF microparticles XPS spectra were determined by an X-ray photoelectron spectrometer (AXIS SUPRA, Shimadzu, Japan) equipped with monochromatic Al Kα (E\u0026thinsp;=\u0026thinsp;1486.6 eV) radiation. The measured XPS energies were collected using the C1s peak of the C\u0026ndash;C bond at 284.6 eV.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003ePowder X-ray Diffraction (XRD)\u003c/h2\u003e \u003cp\u003eThe crystal phase analyses of the resulting MOF microparticles were carried out at room temperature using X-ray diffractometer (D8 ADVANCE, Bruker, Germany) with a generator voltage of 40 kV and a 2\u003cem\u003eθ\u003c/em\u003e range of 5\u0026thinsp;~\u0026thinsp;70\u0026deg;. Here the scanning speed was set as 5\u0026deg;/minute.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eDynamic light scattering (DLS) \u0026amp; Zeta potential analysis\u003c/h2\u003e \u003cp\u003eThe colloidal properties of the resulting MOF microparticles were measured using a nanoparticle size \u0026amp; Zeta potential analyzer (NanoBrook 90 plus PALS, Brookhaven, U.S.A.). Here the sample was the isododecane dispersion solution of the resulting MOF microparticles with a fixed concentration of 0.02 mg/mL. Typically, the resulting autocorrelation functions were analyzed using built-in software to extract hydrodynamic dimensions and polydispersity (PDI). And the auto-balanced voltage values and default parameters was used to obtain the Zeta potential.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eElectrophoretic characterizations of polymer-reinforced MOF microparticles\u003c/h2\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003ePreparation of colored electrophoretic inks based on polymer-reinforced MOF microparticles\u003c/h2\u003e \u003cp\u003eTypically, 0.1 g of the resulting M-BTC-PEI (M\u0026thinsp;=\u0026thinsp;Cu, Fe, Ni, Co) microparticle was ultrasonically dispersed into 1 mL of the isododecane solution of PIBSA (50 mg/mL) to obtain positively charged colored electrophoretic ink.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of white electrophoretic ink\u003c/h2\u003e \u003cp\u003eTypically, 0.1 g of the modified TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles was ultrasonically dispersed in 1 mL of the isododecane solution of PIBSA (50 mg/mL) to obtain positively charged white electrophoretic ink.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eFabrication of two-color electrophoretic display cell\u003c/h2\u003e \u003cp\u003eJust as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB, the adopted display cell comprised two parallel ITO glass plates (3 cm\u0026times;3 cm) with the inner face-to-face ITO layers and the fixed spacing distance (100 \u0026micro;m) determined by a standard double-sided tape. As the electrophoretic fluid, 1 mL of the colored electrophoretic ink and 0.5 mL of the white electrophoretic ink were ultrasonically mixed to obtain the two-color electrophoretic ink, and then injected into the cell.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eEffect test of electrophoretic display\u003c/h2\u003e \u003cp\u003eDuring the process of electrophoretic display, a predetermined driving voltage of \u0026plusmn;\u0026thinsp;20V was applied through a direct current (DC) power supply (CE0400010T, Earthworm Electronics, P. R. China). Here the display effect was evaluated by reflectance, response time, and color coordinates using a high-speed reflectometer (Admesy, Netherlands), according to CIE (Commission Internationale de I' \u0026Eacute;clairage) color space standard.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by the Program for\u0026nbsp;Guangdong Innovative and Entrepreneurial Teams (No. 2019BT02C241), Guangdong Provincial Key Laboratory of Optical Information Materials and Technology (No. 2023B1212060065), MOE International Laboratory for Optical Information Technologies, Startup Foundation from SCNU, and the 111 Project.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor details\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding Author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHao Li - South China Normal University, Guangzhou, China; orcid.org/0000-0003-1744-1526; Phone: +86-20-39314813; Email:\u0026nbsp;[email protected];\u0026nbsp;Fax: +86-20-39314813.\u003c/p\u003e\n\u003cp\u003eGuofu Zhou − South China Normal University, Guangzhou, China; orcid.org/0000-0003-1101-1947; Phone: +86-20-39314813; Email:\u0026nbsp;[email protected];\u0026nbsp;Fax: +86-20-39314813.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJiamin Cheng − South China Normal University, Guangzhou, China\u003c/p\u003e\n\u003cp\u003eMian Qin − South China Normal University, Guangzhou, China\u003c/p\u003e\n\u003cp\u003eWenhao Wang − South China Normal University, Guangzhou, China\u003c/p\u003e\n\u003cp\u003eJingxing Zhang − South China Normal University, Guangzhou, China\u003c/p\u003e\n\u003cp\u003eYao Wang\u0026nbsp;- South China Normal University, Guangzhou, China; orcid.org/0000-0002-0713-5018;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere are no conflicts to declare.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eYe, S., Hosono, N. \u0026amp; Uemura, T. 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J.\u003c/em\u003e\u003cstrong\u003e430\u003c/strong\u003e, 132891 (2022).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"light-science-and-applications","isNatureJournal":false,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"lsa","sideBox":"Learn more about [Light: Science \u0026 Applications](http://www.nature.com/lsa/)","snPcode":"41377","submissionUrl":"https://mts-lsa.nature.com/","title":"Light: Science \u0026 Applications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Metal-organic framework, Polymer-reinforced, Color particle, High charge density, Electrophoretic display","lastPublishedDoi":"10.21203/rs.3.rs-6249755/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6249755/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBesides high porosity and controllable structure, metal-organic framework (MOF) has some natural advantages for color electrophoretic particles: easy modification, controllable morphology, low and adjustable density, and high charge density, as well as rich, vivid, and stable colors. Therefore, we first integrated the four colored MOF microparticles and polyelectrolytes into the blue, reddish-brown, green, and purple electrophoretic particles, to construct the two-color stable dispersions in nonpolar isododecane as the electrophoretic inks. Here the surface modification of polyethyleneimine (PEI) chains based on non-covalent interaction rendered these MOF microparticles reinforced fully to ~\u0026thinsp;+\u0026thinsp;30 mV in Zeta potential and over 3.6\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e m\u003csup\u003e2\u003c/sup\u003e/V\u0026middot;s in the electrophoretic mobility. Under the ultralow field strength of 0.02 V/\u0026micro;m, all the response time and recovery time were no more than 2.3 and 5.9 seconds, respectively. Even after long-time or multiple driving, these MOF microparticles and their reflectance value still kept constant to some extent. By comparison, these colored PEI-reinforced MOF microparticles are superior to the other organic color pigments and inorganic particles, in response capability, charge-to-mass ratio, preparation method, production cost, and stability in color, particle and display. It is anticipated to provide an innovative and promising technical path for color electrophoresis display.\u003c/p\u003e","manuscriptTitle":"Colored Polymer-reinforced Metal-organic Framework Microparticles with High Charge-to-mass Ratio for Electrophoretic Display","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-17 13:32:55","doi":"10.21203/rs.3.rs-6249755/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"revise","date":"2025-07-04T09:42:35+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"This content is not available.","date":"2025-04-29T17:22:47+00:00","index":3,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2025-04-22T01:16:24+00:00","index":3,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2025-04-21T14:50:28+00:00","index":2,"fulltext":"This content is not available."},{"type":"editorInvitedReview","content":"This content is not available.","date":"2025-04-10T05:52:57+00:00","index":1,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2025-03-28T16:02:48+00:00","index":1,"fulltext":"This content is not available."},{"type":"reviewersInvited","content":"","date":"2025-03-28T14:52:35+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-18T14:11:28+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-18T06:00:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"Light: Science \u0026 Applications","date":"2025-03-18T06:00:12+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"light-science-and-applications","isNatureJournal":false,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"lsa","sideBox":"Learn more about [Light: Science \u0026 Applications](http://www.nature.com/lsa/)","snPcode":"41377","submissionUrl":"https://mts-lsa.nature.com/","title":"Light: Science \u0026 Applications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2fdcf582-bbb7-4f79-829a-8d3a6e5b616c","owner":[],"postedDate":"April 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":46366943,"name":"Physical sciences/Optics and photonics/Optical materials and structures/Nanoparticles"},{"id":46366944,"name":"Physical sciences/Optics and photonics/Applied optics/Displays"}],"tags":[],"updatedAt":"2026-02-25T08:07:56+00:00","versionOfRecord":{"articleIdentity":"rs-6249755","link":"https://doi.org/10.1038/s41377-025-02095-3","journal":{"identity":"light-science-and-applications","isVorOnly":false,"title":"Light: Science \u0026 Applications"},"publishedOn":"2026-02-24 05:00:00","publishedOnDateReadable":"February 24th, 2026"},"versionCreatedAt":"2025-04-17 13:32:55","video":"","vorDoi":"10.1038/s41377-025-02095-3","vorDoiUrl":"https://doi.org/10.1038/s41377-025-02095-3","workflowStages":[]},"version":"v1","identity":"rs-6249755","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6249755","identity":"rs-6249755","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}