Long-range Ordered Graphitic Structure in Silk Fibers Delaminated using Dopamine and Thermal Treatment for Super-Flexible Electronic Textiles

Long-range Ordered Graphitic Structure in Silk Fibers Delaminated using Dopamine and Thermal Treatment for Super-Flexible Electronic Textiles | 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 Research Article Long-range Ordered Graphitic Structure in Silk Fibers Delaminated using Dopamine and Thermal Treatment for Super-Flexible Electronic Textiles Hyun-Seok Jang, Shinik Kim, Ikpyeong Park, Won Taek Jung, Jong Hyeok Seo, and 8 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3281213/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 20 Feb, 2024 Read the published version in Advanced Composites and Hybrid Materials → Version 1 posted 7 You are reading this latest preprint version Abstract Exfoliation has been used to obtain 2D materials with attractive properties, like graphene. The layered structure of silk and its structural transition to a pseudo-graphitic structure by heat treatment has attracted scientific interest because of its potential applications. Here we report that intercalating the silk layers with polydopamine (PDA) followed by thermal treatment delaminates the silk fibers. Cylindrical silk fibers with a diameter of 10 μm changed to graphitic ribbon-like structures with widths of approximately 65 nm. This structural transition was systematically investigated using thermally treated PDA-embedded silks at temperatures from 800 to 1450 °C. The graphitic structures start to be observed at 1000 °C, a much lower heat treatment temperature than previous studies using pure silk. Long-range ordered graphitic structures with a lattice distance of 3.4 Å formed most clearly at 1300 °C. ab-initio molecular dynamics calculations confirmed the microscopic origin of the experimental results. This method allows the fabrication of super-flexible, comparable to pure silk, and high-electrically conductive (277.3 S·cm-1) e-textiles. These thermally treated PDA-embedded silks were also functionalized with Fe2O3 and Bi2Te3 powders using the attachment ability of PDA. This work provides evidence that PDA plays a role in delaminating silk fibers and opens the potential for various applications. Commercial silk Polydopamine Delamination of silk Super-flexible electronic textiles Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction After interesting properties were found in 2D materials such as graphene and transition metal dichalcogenides, growing attention has been focused on the delamination of layered materials to achieve low dimensionality [1-11]. The delamination has been achieved by various methods, for example, mechanical, electrochemical, liquid-phase, and green chemistry approaches [1, 2, 12-15]. In addition to delamination to obtain 2D materials, the intentional thinning of materials can provide advantages of stretchability and flexibility [16, 17] because weak strain and flexibility are inversely proportional to the thickness of a material [18, 19]. Among nature-derived materials, silk has a layered structure. It exhibits a peculiar structure composed of amorphous chains, α -helix structures, and β -sheets (secondary structures). It has tertiary structures, β -crystallites, through hydrophobic/van der Waals interactions between the β -sheets, whose interlayer distances are 3.7 and 5.5 Å [20]. This structure has allowed the extraction of silk nanoribbons [21]. It was reported that β -crystallites were transformed into graphitic structures by heat treatment. However, they were clearly observed at extremely high temperatures (over 2300 °C) [22, 23]. Polydopamine (PDA) has significant structural diversity depending on the synthesis methods [24] and shows exotic properties [25, 26]. From a material science perspective, the most distinctive characteristic of PDA is its attachment ability, offering excellent adhesion properties for most types of substrates or surfaces including noble metals, oxides, semiconductors, ceramics, and synthetic polymers, without additional surface functionalization steps [27, 28]. Here, we demonstrated that cylindrical silk fibers were delaminated into the graphitic ribbon-like laminar structure. This resulted from polymerizing dopamine monomers intercalated into silk fibers, followed by heat treatment. The graphitic structures started to be observed from 1000 °C, which is a much lower heat treatment temperature (HTT) than the previous studies [22, 23]. The evolution of graphitic structures was systematically investigated with thermally treated PDA-embedded silks (TPS) at various temperatures (800 ~ 1450 °C). Long-range ordered graphitic structures with lattice distances of 3.4 Å were most clearly formed at 1300 °C. Using this process to fabricate TPS, we obtained super-flexible electronic textiles (e-textiles). The flexibility of the TPS was almost the same as pure commercial silk (CS), thanks to the bonding ability of the PDA and the breaking of some hydrophobic interactions between the β -sheets in silk during the polymerization of dopamine. The maximum conductivity of the obtained thermally treated PDA-embedded silk (TPS) single fiber was 277.3 S·cm -1 , which was 30 times higher than most e-textiles fabricated from commercial textiles [29]. Using the attachment ability of PDA, we also fabricated functional TPS with Fe 2 O 3 and Bi 2 Te 3 powders to show the possibility of using TPS in various applications. The microscopic origin of the experimental results was also found to be in concert with the theoretical calculations. Materials And Methods 2.1 Reagents Analytical grade raw materials were used as received without further purification, consisting of dopamine hydrochloride (s, 99%, Alfa Aesar), sodium periodate (s, 99.8%, Acros), bismuth(III) telluride (s, 99.99%) and iron(III) oxide (s, 99.995%) from Sigma-Aldrich. Ultrapure deionized water (DI water, > 18 MΩ·cm) was obtained from a Millipore Milli-Q system and was used throughout the experiments. The commercial silk fabric consisted of 16 M/M satin, which was thoroughly rinsed in DI water and sonicated for 30 min to remove any unexpected residues, and dried under N 2 overnight. 2.2 Preparation of Thermally Treated Polydopamine-embedded Silk Dopamine hydrochloride (10~200 mmol) was dispersed in DI water under stirring for 30 min to generate a homogenous dispersion. The commercial silk was placed in the dopamine-containing solution, and then sodium periodate (20~400 mmol) was dispersed in the DI water and stirred for 10 min. Subsequently, the two solutions were mixed vigorously with a magnetic stirrer under ambient conditions to embed the dopamine via the polymerization process into the silk in a homogeneous manner. After stirring for 12 h, the polydopamine embedded silk (PDA-silk) was washed with DI water 3 times and dried in a vacuum. The dried PDA-silk was placed in a tubular furnace (DVF-1600, Daeheung Sci. Korea) and thermal treatment proceeded under ambient Ar/H 2 96/4% conditions, with a flow rate of 700 cc·min -1 . First, the PDA-silk-loaded tubular furnace was purged using Ar/H 2 gas for 30 min. Then, the temperature was increased from room temperature to 200 °C to a target temperature of 800~1400 °C with a speed of 5 °C·min -1 . The temperature was maintained at 200 °C, with target temperatures occurring at 1 h and 3 h, respectively. For functionalized TPS, 8 mg·mL -1 of Fe 2 O 3 (or Bi 2 Te 3 ) solution was added into the PDA@Silk solution with constant stirring for 12 h to make Fe 2 O 3 (or Bi 2 Te 3 )@PDA@SilK composites. The obtained sample was washed with deionized water three times and dried in an electric oven at 60 °C for 6 h. 2.3 Structural Characterizations To observe the morphology and atomic structures of the samples, FE-SEM (JSM-7800F, JEOL, Japan) and FE-TEM (Talos F200X, Thermo Fisher Scientific, USA) analyses were used. Structural analysis was conducted by TEM using a Tecnai F30 microscope (FEI, Netherlands), with a point-to-point resolution of 0.2 nm, operating at 300 kV. The XPS (PHI 5000 Veras Probe II, Chigasaki, Japan) spectra were obtained using a monochromatic Al-Κα radiation source, while the Raman spectra (XperRF, Nanobase, Korea) were obtained by 532 nm laser excitation. 2.4 Measurement of the Electrical Properties The electrical characteristics of all samples were assessed using a conventional 4-probe method using a Keithley6221 current source and Keithley 2182A nanovoltmeter (Keithley, USA). The variation in resistance as a function of bending cycles was measured by a homemade 2-probe bending device with a model 4200-SCS semiconductor characterization system (Keithley, USA). Thermoelectric power was measured using a low frequency AC (10 mHz) steady-state method with Keithley6221 and Keithley2182A at room temperature. 2.5 Ab-initio Molecular Dynamics Calculations The ab-initio molecular dynamics calculations (AIMD) simulations conducted in this work were carried out using the Vienna ab Initio Simulation Package [30]. The Perdew-Burke-Ernzerhof functional of the generalized gradient approximation [31] was used to treat the exchange-correlation interactions among the electrons. The cutoff energy of the plane-wave expansion was set to 300 eV, where the Brillouin zone was the sample at the Γ point, and the convergence criterion for the electronic self-consistent loop was set to 1 meV. The timestep of AIMD was 0.5 fs and the radial distribution functions were calculated after 3.5 ps of time evolution. In the supercells, each of the three 5,6-dihydroxyindole and dopamine quinone molecules [32] were placed between the laterally extended β-sheets consisting of 408 C, N, O, and H atoms. Results And Discussion 3.1 Long-Range Ordered Graphitic Structure of TPS The TPS was fabricated by simply dipping the CS into a bath containing 30 mM dopamine, which was polymerized by the addition of NaIO 4 following pyrolysis at various HTTs (Fig. S1a-d. The samples were labeled according to their HTT, i.e., TPS1300 indicates TPS prepared at 1300 °C). The HTT-dependent morphology of the TPSs was observed with SEM (Fig. S1e-g and Fig. S2). Particles were found on the surface of the TPS, resulting from the PDA coating on the surface (Fig. S1g and Fig. S2). We focused on the formation of a ribbon-like structure. During the initial synthesis process, the dopamine monomers were intercalated between the β -sheets in the β -crystallites. Then, the intercalated dopamine monomers were polymerized, which caused the binding interactions between the β -sheets to weaken, breaking the interactions. The additional heat treatment enhanced delamination and finally formed the graphitic structures (Fig. 1a). Before heat treatment, the PDA-embedded silk (30 mM of PDA) had a larger fiber diameter than the pristine silk (Left inset of Fig. 1b and Fig. S4b). This was the result of two locations for attaching the PDA, i.e., PDAs inside and outside the fibers. After heat treatment, TPS1300, the fiber diameter significantly decreased and the cylindrical shape of the fibers changed to a ribbon-like structure (Fig. 1b). The thickness of TPS1300 was thinner than Silk1300 (Right inset of Fig. 1b). Furthermore, the thermal energy (Fig. 1c) and molar concentration (Figs. S3-S5) caused the thickness of the fiber to be much thinner, e.g., from 11.9 μm for PDA-embedded silk to 2.7 μm for TPS1450. AFM image of TPS1300 ribbon fabricated with 30 mM of PDA shows that the thickness is down to ~ 65 nm (Fig. 1d and e). The line profile shows that the width and height of TPS1300 ribbon are 370 nm and 65 nm, respectively. Raman spectroscopy of the ribbon shows that TPS1300 has a graphitic structure (Fig. 1f). The HTT-dependent structural change observed with Raman spectroscopy will be discussed later. Figure 1g displays the SEM image of another TPS1300 ribbon. The small particles originating from PDA were observed even in the TPS1300 ribbon. This is evidence that the dopamine monomers were polymerized inside the silk fibers. The same approach has been adopted for the fabrication of TPS from various textiles, namely, wool, cotton, hemp, nylon, and polyester, to prove the role of the unique structure of silk. Although we found an increase in diameter due to the PDA coating and shrinkage of the fiber after heat treatment (Figs. S6-S10 and Table S1), delamination of the fibers was not observed among the five textiles. 3.2 Atomic Structure of the HTT-Dependent TPS The structural changes in the HTT-dependent TPS are depicted in Fig. 2. No clear crystalline region was found in TPS800 (Fig. 2a). The ordered graphitic structures were initially observed at an HTT of 1000 °C and then became more significant until an HTT of 1300 °C (Fig. 2b-d). This showed that the PDA played a key role in steeply reducing the HTT needed to form highly-ordered graphitic structures down to 1000 °C, compared with the previous reports on thermally treated silk (2300 °C) [22, 23]. Highly crystalline and long-range ordered graphitic structures were observed in TPS1300. Above an HTT of 1350 °C, broken crystalline structures and a relatively small crystalline region started to occur. Figure 2e-g shows that the ordered graphitic structures were opened or broken down (union-like graphitic structure) as the HTT increased from 1350 to 1450 °C. The fast Fourier transform (FFT) patterns in the insets of Fig. 2a-g show similar tendencies. Above an HTT of 1000 °C, the samples exhibited two ring patterns, where the measured distances were 2.14 and 3.40 Å. A d -spacing of 2.14 Å corresponds to the (100) plane, and 3.40 Å matches well with the average interlayer distance of graphitic structures, (002) plane. They became clearer up to TPS1300, weakened in TPS1350 and TPS1400, and finally, were rarely observed in TPS1450. Figure S11 displays four randomly measured regions in TEM images and the calculated average value, to determine the lattice distances of TPS1300 and TPS1350. The obtained lattice distances are well consistent with the interlayer distance of graphitic structure (3.40 Å) from FFT analysis. The structural change was also investigated by Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). Unlike the Raman spectrum of the PDA-embedded silk before heat treatment (Fig. S12c), after the heat treatment of TPS at 800 °C, broad D , G , and 2D bands were clearly observed at 1364, 1603, and near 2800 cm −1 , respectively, indicating the graphitic structures of the TPS (Figs. S13a and S14a). The results are presented in detail in Supplementary Information (Figs. S12-S14 and Table S2). The results obtained from Raman spectroscopy indicated that the amount of oxygen, -OH, and -NH contained in the PDA and silk decreased and a graphitic structure with defects formed [33] as HTT increased. This behavior was also identified in the XPS study. The results obtained from XPS accord with the results from TEM and Raman spectroscopy (Figs. S15-S22 and Table S3). We focused on the HTT-dependent π-π* shake-up feature (Fig. 2h), which was attributed to the aromatic structure of the benzene ring [34]. With an increase in HTT, the π-π* shake-up feature increased to an HTT of 1300 °C, but was decreased from 1350 °C. This indicates that aromatic rings formed and increased as the HTT increased up to 1300 °C. At 1350 °C, the aromatic rings started to be broken due to thermal energy. Hence, we suggest that these crystalline peaks (2.14 and 3.40 Å) with the highly oriented graphitic structure in the TEM study could originate from the crosslinking and cyclization of the protein strands in silk. The functional groups in the dopamine monomer (5,6-dihydroxyindole) can generate intermolecular bonding with an oriented structure between each of the β -sheets. Further heat treatment processes boost the formation of aromatic rings in the TPS, leading to a long-range ordered graphitic structure at a relatively low temperature of 1300 °C. We also compared TEM images of silk without PDA, that were thermally treated at the same temperature of 1300 °C, to determine the critical role of PDA, as well as its effects on the crystal structures of β -sheets/crystallite in silk. Discernable lattice fringes were rarely found in Silk1300 (Fig. S23). 3.3 Molecular Dynamics Calculations of the β -sheets and Dopamine at Various Temperatures To understand the intriguing variations in the TPS structure caused by thermal energy, we performed ab-initio molecular dynamics (MD) calculations, in which the dopamine molecules were placed between β -sheets. Figure 3a shows the intermolecular radial distribution function in the atomic bonds between the β -sheets and dopamine molecules, which was absent at a low temperature (500 K), substantially developed at 1100 K, and decreased at a high temperature (1700 K). At elevated temperatures, the snapshots of the MD calculations demonstrated the presence of intermolecular bonding that was suppressed at low temperatures (Fig. 3b and Movie S1). By contrast, the β -sheets became fractionalized by thermal energy, as shown in the radial distribution function in Fig. 3c. The peak at 1.5 Å monotonically decreased with temperature, indicating the breakdown of β -sheets at high temperatures. The MD results exhibited that the decomposition of the β -sheets was achieved by thermal fluctuations without the aid of external dopamine molecules (Fig. 3d and Movie S2). Therefore, the macroscopic structure is likely to be determined by two competing factors, namely, the development of intermolecular bonds and the breakdown of β -sheets, leading to an optimal temperature at which bond formation is facilitated, and the collapse of the β -sheets diminished. In the experimental results, this temperature was around 1300 °C. 3.4 Super-Flexible Electronic Textiles and the Possibility for Various Applications The long-range ordered graphitic structure resulting from the delamination of silk with heat treatment gives the TPSs superior flexibility as well as high electrical conductivity. Graphene oxide-coated silk [35] and thermally-treated silk (pyroprotein) with axial tension [36] with an HTT over 900 °C have been shown to be unstable when bending. In contrast, the blue LED lights connected to TPS1300 continued to operate even under twisting (Fig. 4a) and repeated grabbing (Fig. 4b and Movie S3). This was also confirmed by the bending cycle-dependent resistance ( R ) of TPS1300, where the variation in R was 0.6% for R 0 ( R of the initial state) (Fig. S24). Exploiting this super-flexibility, we then fabricated long TPS1300 yarn (over 130 cm, Fig. S25) for knitting (Fig. S26 and Movie S4). Although the flexibility was not close to that of the TPS, flexibility was also observed in thermally treated PDA-embedded (TP) wool and cotton at 900 °C, which was ascribed to the bonding ability of the PDA (Fig. S27 and Movie S5). Figure 4c displays the HTT-dependent conductivity of TPS single fibers, which increased from 12.48 S·cm -1 for TPS800 to 277.3 S·cm -1 for TPS1300. However, at an HTT of 1350 °C, the conductivity decreased to 193.0 S·cm -1 for TPS1450, and the same tendency was found in the TPS fabrics (Fig. 4d). In addition, the conductivity of a TPS900 single fiber (46.3 S·cm -1 ) was higher than that of silk fiber (18.8 S·cm -1 ) treated at 900 °C (Silk900). For the comparison of conductivity, we treated both samples at 900 °C because the heat-treated silk did not remain flexible above an HTT of 900 °C. The bonding of PDA to the chemical compositions ( α -helixes, β -sheets, and random-coils) of the silk fibers and the carbonization of TPS played an essential role in the observed high conductivity. The TPS structural change explains the behavior of the HTT-dependent electrical conductivity. That is, the HTT-dependent conductivity is closely related to the evolution of its graphitic structure, as shown in the TEM study and the π-π* shake-up feature. The increase in conductivity from TPS800 to TPS1300 originated from the increase in ordered graphitic structures. Above 1350 °C, the crystal size became too small to produce sufficient electrical conducting paths in the TPS compared to TPS1300. Hence low conductivity was observed in the TPS treated above 1350 °C. To further investigate the attachment ability of PDA, magnetic textiles were fabricated using Fe 2 O 3 powders. The fabrics were obtained by simply mixing the powders in when PDA was embedded in the silk. SEM images and energy dispersive spectroscopy (EDS) elemental mapping in Fig. 4e-h show that Fe 2 O 3 particles were well coated onto the silk fiber surface due to PDA. The magnetic property was exhibited by this fabric. We observed an attracting force between the fabric and magnet (Fig. 4i and j, Movie S6). We also fabricated functionalized fabrics with Bi 2 Te 3 powders (Fig. S28). Although improvement is needed, the Bi 2 Te 3 -coated TPS thermally treated at 550 °C showed potential for use as a flexible thermoelectric material. Its thermoelectric power was -32.3 μV·K -1 at 300 K, which is comparable to previous reports for flexible thermoelectric devices fabricated with carbon materials [37-39]. Conclusion In summary, embedding PDA into silk and the subsequent polymerization of the dopamine monomers caused the silk fiber to swell. After heat treatment, the cylindrical silk fibers changed to a laminar shape, which was caused by the delamination of β -crystallites in the silk. Long-range ordered structures with a lattice distance of 3.4 Å formed at a treatment temperature of around 1300 °C. The resulting TPS exhibited super-flexibility and was electrical conducting. This process was also investigated by molecular dynamics calculations, which analyzed the interaction between the dopamine and β -sheets. The results were well consistent with the experimental results. These results confirm that, by exploiting the attachment ability of PDA and delamination of silk fibers, TPS has potential uses in various applications such as a clothing-based generator, using electromagnetic induction and thermoelectric textiles. Declarations Conflicts of interest The authors declare no competing interests. Acknowledgements H.–S. J., S. K., and I. P. contributed equally to this work. The authors thank Prof. H. R. Moon, J. S. Kim, and H.-J. Jin for their valuable comments. Funding B.H.K. was supported by the National Research Foundation of Korea (NRF) by the Korea Government (MSIT) (NRF-2020R1A2C4001513). Y.K. was supported by the National Research Foundation of Korea (NRF) by the Korea Government (MSIT) (NRF-2021R1F1A106411113). J.K. was supported by the National Research Foundation of Korea (NRF) by the Korea Government (MSIT) (NRF-2022R1F1A1059616). 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J Mater Chem 20:10829-10834. http://doi.org/10.1039/c0jm01799j Jeon JW, Cho SY, Jeong YJ, Shin DS, Kim NR, Yun YS, Kim H-T, Choi SB, Hong WG, Kim HJ, Jin H-J, Kim BH (2017) Pyroprotein-based electronic textiles with high stability. Adv Mater 29:1605479. http://doi.org/10.1002/adma.201605479 Jeon JW, Oh JY, Cho SY, Lee S, Jang H-S, Jung WT, Kim J-G, Kim H, Kim HJ, Kim SY, Han S, Kim J, Chang YJ, Suh D, Jin H-J, Kim BH (2018) Pyroprotein-based electronic textiles with high thermal durability. Mater Today 21:944-950. https://doi.org/10.1016/j.mattod.2018.03.038 Ito M, Koizumi T, Kojima H, Saito T, Nakamura M (2017) From materials to device design of a thermoelectric fabric for wearable energy harvesters. J Mater Chem A 5:12068-12072. http://doi.org/10.1039/c7ta00304h Lee M-H, Kang YH, Kim J, Lee YK, Cho SY (2019) Freely shapable and 3D porous carbon nanotube foam using rapid solvent evaporation method for flexible thermoelectric power generators. Adv Energy Mater 9:1900914. http://doi.org/10.1002/aenm.201900914 Liu Y, Khavrus V, Lehmann T, Yang H-I, Stepien L, Greifzu M, Oswald S, Gemming T, Bezugly V, Cuniberti G (2020) Boron-doped single-walled carbon nanotubes with enhanced thermoelectric power factor for flexible thermoelectric devices. ACS Appl Energy Mater 3:2556-2564. http://doi.org/10.1021/acsaem.9b02243 Additional Declarations No competing interests reported. Supplementary Files MovieS1.mp4 MovieS2.mp4 MovieS3.mp4 MovieS4.mp4 MovieS5.mp4 SupplementaryInformation.pdf Cite Share Download PDF Status: Published Journal Publication published 20 Feb, 2024 Read the published version in Advanced Composites and Hybrid Materials → Version 1 posted Editorial decision: Major revision 27 Sep, 2023 Reviews received at journal 23 Sep, 2023 Reviewers agreed at journal 18 Sep, 2023 Reviewers invited by journal 18 Sep, 2023 Editor assigned by journal 08 Sep, 2023 Submission checks completed at journal 25 Aug, 2023 First submitted to journal 21 Aug, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-3281213","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":228770517,"identity":"d6e99fda-527e-44e4-98c2-e94eb287c1a7","order_by":0,"name":"Hyun-Seok Jang","email":"","orcid":"","institution":"Incheon National University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hyun-Seok","middleName":"","lastName":"Jang","suffix":""},{"id":228770518,"identity":"c2793dd4-0730-4d1f-9725-16c2b74443c6","order_by":1,"name":"Shinik Kim","email":"","orcid":"","institution":"Konkuk University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Shinik","middleName":"","lastName":"Kim","suffix":""},{"id":228770519,"identity":"e287b266-c5c0-4e01-8045-27b5871a6612","order_by":2,"name":"Ikpyeong Park","email":"","orcid":"","institution":"Incheon National University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ikpyeong","middleName":"","lastName":"Park","suffix":""},{"id":228770520,"identity":"914d5193-cb2b-4ae7-8c27-52b1aedd9cf2","order_by":3,"name":"Won Taek Jung","email":"","orcid":"","institution":"Incheon National University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Won","middleName":"Taek","lastName":"Jung","suffix":""},{"id":228770521,"identity":"f4c3398f-f1bb-47b9-a613-0eff80a70dc1","order_by":4,"name":"Jong Hyeok Seo","email":"","orcid":"","institution":"Korea Research Institute of Standards and Science","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jong","middleName":"Hyeok","lastName":"Seo","suffix":""},{"id":228770522,"identity":"3f1e55d1-d5ab-46b0-9eb0-6fbeb9089abe","order_by":5,"name":"Ji-Hwan Kwon","email":"","orcid":"","institution":"Korea Research Institute of Standards and Science","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ji-Hwan","middleName":"","lastName":"Kwon","suffix":""},{"id":228770523,"identity":"051168f3-c5cf-45bc-9040-575a5851fdbe","order_by":6,"name":"Won G. Hong","email":"","orcid":"","institution":"Korea Basic Science Institute","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Won","middleName":"G.","lastName":"Hong","suffix":""},{"id":228770524,"identity":"92cd79e9-6b78-46c6-9425-6da6487512d7","order_by":7,"name":"Radosław Mrówczyński","email":"","orcid":"","institution":"Adam Mickiewicz University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Radosław","middleName":"","lastName":"Mrówczyński","suffix":""},{"id":228770525,"identity":"d62ee607-4888-4317-9481-f864046e9902","order_by":8,"name":"Heewoo Lee","email":"","orcid":"","institution":"Incheon National University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Heewoo","middleName":"","lastName":"Lee","suffix":""},{"id":228770526,"identity":"290d56cb-141e-4090-8e9e-cd4256c8c0bc","order_by":9,"name":"Soo Bong Choi","email":"","orcid":"","institution":"Incheon National University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Soo","middleName":"Bong","lastName":"Choi","suffix":""},{"id":228770527,"identity":"961b35c3-b2be-4457-b58d-b6703ae8bb34","order_by":10,"name":"Jeongwoo Kim","email":"","orcid":"","institution":"Incheon National University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jeongwoo","middleName":"","lastName":"Kim","suffix":""},{"id":228770528,"identity":"1869112d-59db-4544-b6ab-fcd5b32a923a","order_by":11,"name":"Yeonho Kim","email":"","orcid":"","institution":"Konkuk University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yeonho","middleName":"","lastName":"Kim","suffix":""},{"id":228770529,"identity":"1236638c-4904-4589-917d-f431613801a2","order_by":12,"name":"Byung Hoon Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtklEQVRIiWNgGAWjYBACCQke5sd/KiSg3APEaWEz4DlDohYGCd42GJcYLZKzew8YSM6zyDM4wPzwA8OZe4S1SMucS3hguE2i2OAAm7EEw41iwlrkJHIMDBK3SSRuOMBgxsDwIYE4LRIH54C0sH8jTos0UItkYwNICw/QlhtEaJGcc8bMmOGYROLMwzzFEglniNAicbvH+DFDTV1i3/H2jR8+HCNCCwIwAzFJGkbBKBgFo2AU4AYAwKs3VurSUlkAAAAASUVORK5CYII=","orcid":"","institution":"Incheon National University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Byung","middleName":"Hoon","lastName":"Kim","suffix":""}],"badges":[],"createdAt":"2023-08-21 06:14:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3281213/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3281213/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s42114-024-00857-y","type":"published","date":"2024-02-20T15:00:37+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":42311562,"identity":"c1ad3ce2-5b30-4678-8bf7-d66cc60186d8","added_by":"auto","created_at":"2023-08-29 14:36:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":259477,"visible":true,"origin":"","legend":"\u003cp\u003eDelamination of silk due to PDA and thermal treatment.\u003cstrong\u003e a\u003c/strong\u003eSchematic illustration of delamination of silk fiber. \u003cstrong\u003eb\u003c/strong\u003e SEM images of TPS1300, PDA-embedded silk (left inset), and Silk1300 (right inset). Laminar structures were observed differently in Silk1300. The scale bars in the insets are 10 μm. \u003cstrong\u003ec\u003c/strong\u003e HTT-dependent average diameters (or widths) were obtained from SEM images, where each averaged diameter was calculated with over 200 fibers. \u003cstrong\u003ed\u003c/strong\u003e AFM topography and \u003cstrong\u003ee\u003c/strong\u003eline profile of TPS1300. \u003cstrong\u003ef\u003c/strong\u003e \u003cem\u003eD\u003c/em\u003e and \u003cem\u003eG\u003c/em\u003e peaks obtained from Raman spectroscopy of the TPS1300. \u003cstrong\u003eg\u003c/strong\u003e SEM image of another TPS1300. Small particles can be observed\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/32f09221c1d1d804f65527ab.png"},{"id":42311564,"identity":"b025b6da-0983-4408-b3fc-cf502b82eb21","added_by":"auto","created_at":"2023-08-29 14:36:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":447196,"visible":true,"origin":"","legend":"\u003cp\u003eHTT-dependent structural evolution. TEM images for \u003cstrong\u003ea\u003c/strong\u003e TPS800, \u003cstrong\u003eb\u003c/strong\u003e TPS1000, \u003cstrong\u003ec\u003c/strong\u003e TPS1200, \u003cstrong\u003ed \u003c/strong\u003eTPS1300, \u003cstrong\u003ee\u003c/strong\u003e TPS1350, \u003cstrong\u003ef\u003c/strong\u003e TPS1400, and \u003cstrong\u003eg\u003c/strong\u003e TPS1450. The insets are the FFT corresponding to each TEM image. \u003cstrong\u003eh\u003c/strong\u003eHTT-dependent π-π* shake-up feature obtained from XPS\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/c91cb703a3a2dc91582b82aa.png"},{"id":42312400,"identity":"ba14ec73-071b-4107-826f-8a649188c73f","added_by":"auto","created_at":"2023-08-29 14:44:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":167395,"visible":true,"origin":"","legend":"\u003cp\u003eMolecular dynamics simulations of the \u003cem\u003eβ\u003c/em\u003e-sheets and dopamine molecules. \u003cstrong\u003ea\u003c/strong\u003e The radial distribution function of the intermolecular bonding between the \u003cem\u003eβ\u003c/em\u003e-sheets and dopamine molecules (DMs) for 500, 1100, and 1700 K. The gray region denotes the range of atomic bonding distance of the C, N, and O atoms. \u003cstrong\u003eb\u003c/strong\u003e Atomic configurations of the intermolecular bonding between the \u003cem\u003eβ\u003c/em\u003e-sheets (orange sphere) and DMs (blue spheres) for 500, 1100, and 1700 K. \u003cstrong\u003ec\u003c/strong\u003eRadial distribution functions of the \u003cem\u003eβ\u003c/em\u003e-sheets at 500, 1100, and 1700 K, where the gray region denotes the range of atomic bonding distance of the C, N, and O atoms. \u003cstrong\u003ed\u003c/strong\u003eDecomposition of the \u003cem\u003eβ\u003c/em\u003e-sheets at 1700 K. The distance between certain constituent atoms (purple spheres) of the \u003cem\u003eβ\u003c/em\u003e-sheets increased with time\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/40d8d7597c7d9ee0dd1b381f.png"},{"id":42312401,"identity":"1b0749ef-ca82-478b-b70b-3fe88c29e9db","added_by":"auto","created_at":"2023-08-29 14:44:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":488752,"visible":true,"origin":"","legend":"\u003cp\u003eSuper-flexible electronic textiles and their application. Stability of TPS1300 after \u003cstrong\u003ea\u003c/strong\u003e twisting and \u003cstrong\u003eb\u003c/strong\u003e repeated grabbing. The HTT-dependent conductivity of \u003cstrong\u003ec\u003c/strong\u003e a single silk fiber and \u003cstrong\u003ed\u003c/strong\u003e TPS fabrics. The conductivity increased until 1300 °C HTT, but decreased at 1350 °C. The lower conductivity of the fabric compared to the single fiber was attributed to the poor electrical contact between the fibers comprising the fabric. \u003cstrong\u003ee\u003c/strong\u003e SEM image and EDS elemental mapping of \u003cstrong\u003ef\u003c/strong\u003e C, \u003cstrong\u003eg\u003c/strong\u003e O, and \u003cstrong\u003eh\u003c/strong\u003e Fe of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e coated silk. \u003cstrong\u003ei-j\u003c/strong\u003e The magnetic attraction between Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-coated silk fabric and a 0.11 T magnet. The attraction started to occur at a distance of 2.6 cm\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/e28fe35511ce0649b763e235.png"},{"id":51648158,"identity":"3efea119-dcf5-4ec1-aa52-44334ec3a172","added_by":"auto","created_at":"2024-02-26 15:07:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1507705,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/5fec97f2-3ce2-4f40-bd6a-d7fcf5a9f251.pdf"},{"id":42311568,"identity":"6ecb44a9-49e8-4a2e-a488-9bcde1496b44","added_by":"auto","created_at":"2023-08-29 14:36:10","extension":"mp4","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":2412025,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/e5e818baf84ee455d728ed0f.mp4"},{"id":42311565,"identity":"c3260ce3-b757-4642-832c-5d81e69b4f13","added_by":"auto","created_at":"2023-08-29 14:36:10","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1806648,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/d7c0438f8f01387152cb5f53.mp4"},{"id":42311572,"identity":"863e5b13-9767-4dae-b4e8-8d33bd9c99b8","added_by":"auto","created_at":"2023-08-29 14:36:12","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":19142927,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/cd6063f21c8e69eec0c7b43a.mp4"},{"id":42311570,"identity":"a56a6a85-98ec-454a-8755-1aba47fd13f9","added_by":"auto","created_at":"2023-08-29 14:36:12","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":17215500,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS4.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/cc5939a85d3dbd67d4e476fe.mp4"},{"id":42311571,"identity":"ddcfd2ec-13f0-4a6d-a105-b98ad6a383a7","added_by":"auto","created_at":"2023-08-29 14:36:12","extension":"mp4","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":19476634,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS5.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/1d26e36d2261fe30dfc3c4c6.mp4"},{"id":42311569,"identity":"c12803c9-9f59-4051-ad4b-cb15f36ba46e","added_by":"auto","created_at":"2023-08-29 14:36:11","extension":"pdf","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":5433583,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3281213/v1/db8bd96f0efc6ea359bcc05c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Long-range Ordered Graphitic Structure in Silk Fibers Delaminated using Dopamine and Thermal Treatment for Super-Flexible Electronic Textiles","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAfter interesting properties were found in 2D materials such as graphene and transition metal dichalcogenides, growing attention has been focused on the delamination of layered materials to achieve low dimensionality [1-11]. The delamination has been achieved by various methods, for example, mechanical, electrochemical, liquid-phase, and green chemistry approaches [1, 2, 12-15]. In addition to delamination to obtain 2D materials, the intentional thinning of materials can provide advantages of stretchability and flexibility [16, 17] because weak strain and flexibility are inversely proportional to the thickness of a material [18, 19]. Among nature-derived materials, silk has a layered structure. It exhibits a peculiar structure composed of amorphous chains, \u003cem\u003e\u0026alpha;\u003c/em\u003e-helix structures, and \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets (secondary structures). It has tertiary structures, \u003cem\u003e\u0026beta;\u003c/em\u003e-crystallites, through hydrophobic/van der Waals interactions between the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets, whose interlayer distances are 3.7 and 5.5 \u0026Aring; [20]. This structure has allowed the extraction of silk nanoribbons [21]. It was reported that \u003cem\u003e\u0026beta;\u003c/em\u003e-crystallites were transformed into graphitic structures by heat treatment. However, they were clearly observed at extremely high temperatures (over 2300 \u0026deg;C) [22, 23].\u003c/p\u003e\n\u003cp\u003ePolydopamine (PDA) has significant structural diversity depending on the synthesis methods [24] and shows exotic properties [25, 26]. From a material science perspective, the most distinctive characteristic of PDA is its attachment ability, offering excellent adhesion properties for most types of substrates or surfaces including noble metals, oxides, semiconductors, ceramics, and synthetic polymers, without additional surface functionalization steps [27, 28].\u003c/p\u003e\n\u003cp\u003eHere, we demonstrated that cylindrical silk fibers were delaminated into the graphitic ribbon-like laminar structure. This resulted from polymerizing dopamine monomers intercalated into silk fibers, followed by heat treatment. The graphitic structures started to be observed from 1000 \u0026deg;C, which is a much lower heat treatment temperature (HTT) than the previous studies [22, 23]. The evolution of graphitic structures was systematically investigated with thermally treated PDA-embedded silks (TPS) at various temperatures (800 ~ 1450 \u0026deg;C). Long-range ordered graphitic structures with lattice distances of 3.4 \u0026Aring; were most clearly formed at 1300 \u0026deg;C. Using this process to fabricate TPS, we obtained super-flexible electronic textiles (e-textiles). The flexibility of the TPS was almost the same as pure commercial silk (CS), thanks to the bonding ability of the PDA and the breaking of some hydrophobic interactions between the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets in silk during the polymerization of dopamine. The maximum conductivity of the obtained thermally treated PDA-embedded silk (TPS) single fiber was 277.3 S\u0026middot;cm\u003csup\u003e-1\u003c/sup\u003e, which was 30 times higher than most e-textiles fabricated from commercial textiles [29]. Using the attachment ability of PDA, we also fabricated functional TPS with Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e powders to show the possibility of using TPS in various applications. The microscopic origin of the experimental results was also found to be in concert with the theoretical calculations.\u003c/p\u003e"},{"header":"Materials And Methods","content":"\u003cp\u003e2.1 Reagents\u003c/p\u003e\n\u003cp\u003eAnalytical grade raw materials were used as received without further purification, consisting of dopamine hydrochloride (s, 99%, Alfa Aesar), sodium periodate (s, 99.8%, Acros), bismuth(III) telluride (s, 99.99%) and iron(III) oxide (s, 99.995%) from Sigma-Aldrich. Ultrapure deionized water (DI water, \u0026gt; 18 M\u0026Omega;\u0026middot;cm) was obtained from a Millipore Milli-Q system and was used throughout the experiments. The commercial silk fabric consisted of 16 M/M satin, which was thoroughly rinsed in DI water and sonicated for 30 min to remove any unexpected residues, and dried under N\u003csub\u003e2\u003c/sub\u003e overnight.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;2.2 Preparation of Thermally Treated Polydopamine-embedded Silk\u003c/p\u003e\n\u003cp\u003eDopamine hydrochloride (10~200 mmol) was dispersed in DI water under stirring for 30 min to generate a homogenous dispersion. The commercial silk was placed in the dopamine-containing solution, and then sodium periodate (20~400 mmol) was dispersed in the DI water and stirred for 10 min. Subsequently, the two solutions were mixed vigorously with a magnetic stirrer under ambient conditions to embed the dopamine via the polymerization process into the silk in a homogeneous manner. After stirring for 12 h, the polydopamine embedded silk (PDA-silk) was washed with DI water 3 times and dried in a vacuum.\u003c/p\u003e\n\u003cp\u003eThe dried PDA-silk was placed in a tubular furnace (DVF-1600, Daeheung Sci. Korea) and thermal treatment proceeded under ambient Ar/H\u003csub\u003e2\u003c/sub\u003e 96/4% conditions, with a flow rate of 700 cc\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e. First, the PDA-silk-loaded tubular furnace was purged using Ar/H\u003csub\u003e2\u003c/sub\u003e gas for 30 min. Then, the temperature was increased from room temperature to 200 \u0026deg;C to a target temperature of 800~1400 \u0026deg;C with a speed of 5 \u0026deg;C\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e. The temperature was maintained at 200 \u0026deg;C, with target temperatures occurring at 1 h and 3 h, respectively. For functionalized TPS, 8 mg\u0026middot;mL\u003csup\u003e-1\u003c/sup\u003e of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (or Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e) solution was added into the PDA@Silk solution with constant stirring for 12 h to make Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (or Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e)@PDA@SilK composites. The obtained sample was washed with deionized water three times and dried in an electric oven at 60 \u0026deg;C for 6 h.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;2.3 Structural Characterizations\u003c/p\u003e\n\u003cp\u003eTo observe the morphology and atomic structures of the samples, FE-SEM (JSM-7800F, JEOL, Japan) and FE-TEM (Talos F200X, Thermo Fisher Scientific, USA) analyses were used. Structural analysis was conducted by TEM using a Tecnai F30 microscope (FEI, Netherlands), with a point-to-point resolution of 0.2 nm, operating at 300 kV. The XPS (PHI 5000 Veras Probe II,\u0026nbsp;Chigasaki, Japan) spectra were obtained using a monochromatic Al-\u0026Kappa;\u0026alpha; radiation source, while the Raman spectra (XperRF, Nanobase, Korea) were obtained by 532 nm laser excitation.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;2.4 Measurement of the Electrical Properties\u003c/p\u003e\n\u003cp\u003eThe electrical characteristics of all samples were assessed using a conventional 4-probe method using a Keithley6221 current source and Keithley 2182A nanovoltmeter (Keithley, USA). The variation in resistance as a function of bending cycles was measured by a homemade 2-probe bending device with a model 4200-SCS semiconductor characterization system (Keithley, USA). Thermoelectric power was measured using a low frequency AC (10 mHz) steady-state method with Keithley6221 and Keithley2182A at room temperature.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;2.5 Ab-initio Molecular Dynamics Calculations\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe \u003cem\u003eab-initio\u003c/em\u003e molecular dynamics calculations (AIMD) simulations conducted in this work were carried out using the Vienna ab Initio Simulation Package [30]. The Perdew-Burke-Ernzerhof functional of the generalized gradient approximation [31] was used to treat the exchange-correlation interactions among the electrons. The cutoff energy of the plane-wave expansion was set to 300 eV, where the Brillouin zone was the sample at the \u0026Gamma; point, and the convergence criterion for the electronic self-consistent loop was set to 1 meV. The timestep of AIMD was 0.5 fs and the radial distribution functions were calculated after 3.5 ps of time evolution. In the supercells, each of the three 5,6-dihydroxyindole and dopamine quinone molecules [32] were placed between the laterally extended \u0026beta;-sheets consisting of 408 C, N, O, and H atoms.\u003c/p\u003e"},{"header":"Results And Discussion","content":"\u003cp\u003e3.1 Long-Range Ordered Graphitic Structure of TPS\u003c/p\u003e\n\u003cp\u003eThe TPS was fabricated by simply dipping the CS into a bath containing 30 mM dopamine, which was polymerized by the addition of NaIO\u003csub\u003e4\u003c/sub\u003e following pyrolysis at various HTTs (Fig. S1a-d. The samples were labeled according to their HTT, i.e., TPS1300 indicates TPS prepared at 1300 \u0026deg;C). The HTT-dependent morphology of the TPSs was observed with SEM (Fig. S1e-g and Fig. S2). Particles were found on the surface of the TPS, resulting from the PDA coating on the surface (Fig. S1g and Fig. S2).\u003c/p\u003e\n\u003cp\u003eWe focused on the formation of a ribbon-like structure. During the initial synthesis process, the dopamine monomers were intercalated between the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets in the \u003cem\u003e\u0026beta;\u003c/em\u003e-crystallites. Then, the intercalated dopamine monomers were polymerized, which caused the binding interactions between the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets to weaken, breaking the interactions. The additional heat treatment enhanced delamination and finally formed the graphitic structures (Fig. 1a). Before heat treatment, the PDA-embedded silk (30 mM of PDA) had a larger fiber diameter than the pristine silk (Left inset of Fig. 1b and Fig. S4b). This was the result of two locations for attaching the PDA, i.e., PDAs inside and outside the fibers. After heat treatment, TPS1300, the fiber diameter significantly decreased and the cylindrical shape of the fibers changed to a ribbon-like structure (Fig. 1b). The thickness of TPS1300 was thinner than Silk1300 (Right inset of Fig. 1b).\u003c/p\u003e\n\u003cp\u003eFurthermore, the thermal energy (Fig. 1c) and molar concentration (Figs. S3-S5) caused the thickness of the fiber to be much thinner, e.g., from 11.9 \u0026mu;m for PDA-embedded silk to 2.7 \u0026mu;m for TPS1450. AFM image of TPS1300 ribbon fabricated with 30 mM of PDA shows that the thickness is down to ~ 65 nm (Fig. 1d and e). The line profile shows that the width and height of TPS1300 ribbon are 370 nm and 65 nm, respectively. Raman spectroscopy of the ribbon shows that TPS1300 has a graphitic structure (Fig. 1f). The HTT-dependent structural change observed with Raman spectroscopy will be discussed later. Figure 1g displays the SEM image of another TPS1300 ribbon. The small particles originating from PDA were observed even in the TPS1300 ribbon. This is evidence that the dopamine monomers were polymerized inside the silk fibers. The same approach has been adopted for the fabrication of TPS from various textiles, namely, wool, cotton, hemp, nylon, and polyester, to prove the role of the unique structure of silk. Although we found an increase in diameter due to the PDA coating and shrinkage of the fiber after heat treatment (Figs. S6-S10 and Table S1), delamination of the fibers was not observed among the five textiles.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;3.2 Atomic Structure of the HTT-Dependent TPS\u003c/p\u003e\n\u003cp\u003eThe structural changes in the HTT-dependent TPS are depicted in Fig. 2. No clear crystalline region was found in TPS800 (Fig. 2a). The ordered graphitic structures were initially observed at an HTT of 1000 \u0026deg;C and then became more significant until an HTT of 1300 \u0026deg;C (Fig. 2b-d). This showed that the PDA played a key role in steeply reducing the HTT needed to form highly-ordered graphitic structures down to 1000 \u0026deg;C, compared with the previous reports on thermally treated silk (2300 \u0026deg;C) [22, 23].\u003c/p\u003e\n\u003cp\u003eHighly crystalline and long-range ordered graphitic structures were observed in TPS1300. Above an HTT of 1350 \u0026deg;C, broken crystalline structures and a relatively small crystalline region started to occur. Figure 2e-g shows that the ordered graphitic structures were opened or broken down (union-like graphitic structure) as the HTT increased from 1350 to 1450 \u0026deg;C. The fast Fourier transform (FFT) patterns in the insets of Fig. 2a-g show similar tendencies. Above an HTT of 1000 \u0026deg;C, the samples exhibited two ring patterns, where the measured distances were 2.14 and 3.40 \u0026Aring;. A \u003cem\u003ed\u003c/em\u003e-spacing of 2.14 \u0026Aring; corresponds to the (100) plane, and 3.40 \u0026Aring; matches well with the average interlayer distance of graphitic structures, (002) plane. They became clearer up to TPS1300, weakened in TPS1350 and TPS1400, and finally, were rarely observed in TPS1450. Figure S11 displays four randomly measured regions in TEM images and the calculated average value, to determine the lattice distances of TPS1300 and TPS1350. The obtained lattice distances are well consistent with the interlayer distance of graphitic structure (3.40 \u0026Aring;) from FFT analysis.\u003c/p\u003e\n\u003cp\u003eThe structural change was also investigated by Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). Unlike the Raman spectrum of the PDA-embedded silk before heat treatment (Fig. S12c), after the heat treatment of TPS at 800 \u0026deg;C, broad \u003cem\u003eD\u003c/em\u003e, \u003cem\u003eG\u003c/em\u003e, and \u003cem\u003e2D\u003c/em\u003e bands were clearly observed at 1364, 1603, and near 2800 cm\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively, indicating the graphitic structures of the TPS (Figs. S13a and S14a). The results are presented in detail in Supplementary Information (Figs. S12-S14 and Table S2). The results obtained from Raman spectroscopy indicated that the amount of oxygen, -OH, and -NH contained in the PDA and silk decreased and a graphitic structure with defects formed [33] as HTT increased. This behavior was also identified in the XPS study. The results obtained from XPS accord with the results from TEM and Raman spectroscopy (Figs. S15-S22 and Table S3).\u003c/p\u003e\n\u003cp\u003eWe focused on the HTT-dependent \u0026pi;-\u0026pi;* shake-up feature (Fig. 2h), which was attributed to the aromatic structure of the benzene ring [34]. With an increase in HTT, the \u0026pi;-\u0026pi;* shake-up feature increased to an HTT of 1300 \u0026deg;C, but was decreased from 1350 \u0026deg;C. This indicates that aromatic rings formed and increased as the HTT increased up to 1300 \u0026deg;C. At 1350 \u0026deg;C, the aromatic rings started to be broken due to thermal energy.\u003c/p\u003e\n\u003cp\u003eHence, we suggest that these crystalline peaks (2.14 and 3.40 \u0026Aring;) with the highly oriented graphitic structure in the TEM study could originate from the crosslinking and cyclization of the protein strands in silk. The functional groups in the dopamine monomer (5,6-dihydroxyindole) can generate intermolecular bonding with an oriented structure between each of the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets. Further heat treatment processes boost the formation of aromatic rings in the TPS, leading to a long-range ordered graphitic structure at a relatively low temperature of 1300 \u0026deg;C. We also compared TEM images of silk without PDA, that were thermally treated at the same temperature of 1300 \u0026deg;C, to determine the critical role of PDA, as well as its effects on the crystal structures of \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets/crystallite in silk. Discernable lattice fringes were rarely found in Silk1300 (Fig. S23).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e3.3 Molecular Dynamics Calculations of the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets and Dopamine at Various Temperatures\u003c/p\u003e\n\u003cp\u003eTo understand the intriguing variations in the TPS structure caused by thermal energy, we performed ab-initio molecular dynamics (MD) calculations, in which the dopamine molecules were placed between \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets. Figure 3a shows the intermolecular radial distribution function in the atomic bonds between the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets and dopamine molecules, which was absent at a low temperature (500 K), substantially developed at 1100 K, and decreased at a high temperature (1700 K). At elevated temperatures, the snapshots of the MD calculations demonstrated the presence of intermolecular bonding that was suppressed at low temperatures (Fig. 3b and Movie S1). By contrast, the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets became fractionalized by thermal energy, as shown in the radial distribution function in Fig. 3c. The peak at 1.5 \u0026Aring; monotonically decreased with temperature, indicating the breakdown of \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets at high temperatures. The MD results exhibited that the decomposition of the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets was achieved by thermal fluctuations without the aid of external dopamine molecules (Fig. 3d and Movie S2). Therefore, the macroscopic structure is likely to be determined by two competing factors, namely, the development of intermolecular bonds and the breakdown of \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets, leading to an optimal temperature at which bond formation is facilitated, and the collapse of the \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets diminished. In the experimental results, this temperature was around 1300 \u0026deg;C.\u003c/p\u003e\n\u003cp\u003e3.4 Super-Flexible Electronic Textiles and the Possibility for Various Applications\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe long-range ordered graphitic structure resulting from the delamination of silk with heat treatment gives the TPSs superior flexibility as well as high electrical conductivity. Graphene oxide-coated silk [35] and thermally-treated silk (pyroprotein) with axial tension [36] with an HTT over 900 \u0026deg;C have been shown to be unstable when bending. In contrast, the blue LED lights connected to TPS1300 continued to operate even under twisting (Fig. 4a) and repeated grabbing (Fig. 4b and Movie S3). This was also confirmed by the bending cycle-dependent resistance (\u003cem\u003eR\u003c/em\u003e) of TPS1300, where the variation in \u003cem\u003eR\u003c/em\u003e was 0.6% for \u003cem\u003eR\u003csub\u003e0\u003c/sub\u003e\u003c/em\u003e (\u003cem\u003eR\u003c/em\u003e of the initial state) (Fig. S24). Exploiting this super-flexibility, we then fabricated long TPS1300 yarn (over 130 cm, Fig. S25) for knitting (Fig. S26 and Movie S4). Although the flexibility was not close to that of the TPS, flexibility was also observed in thermally treated PDA-embedded (TP) wool and cotton at 900 \u0026deg;C, which was ascribed to the bonding ability of the PDA (Fig. S27 and Movie S5).\u003c/p\u003e\n\u003cp\u003eFigure 4c displays the HTT-dependent conductivity of TPS single fibers, which increased from 12.48 S\u0026middot;cm\u003csup\u003e-1\u003c/sup\u003e for TPS800 to 277.3 S\u0026middot;cm\u003csup\u003e-1\u003c/sup\u003e for TPS1300. However, at an HTT of 1350 \u0026deg;C, the conductivity decreased to 193.0 S\u0026middot;cm\u003csup\u003e-1\u003c/sup\u003e for TPS1450, and the same tendency was found in the TPS fabrics (Fig. 4d). In addition, the conductivity of a TPS900 single fiber (46.3 S\u0026middot;cm\u003csup\u003e-1\u003c/sup\u003e) was higher than that of silk fiber (18.8 S\u0026middot;cm\u003csup\u003e-1\u003c/sup\u003e) treated at 900 \u0026deg;C (Silk900). For the comparison of conductivity, we treated both samples at 900 \u0026deg;C because the heat-treated silk did not remain flexible above an HTT of 900 \u0026deg;C.\u003c/p\u003e\n\u003cp\u003eThe bonding of PDA to the chemical compositions (\u003cem\u003e\u0026alpha;\u003c/em\u003e-helixes, \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets, and random-coils) of the silk fibers and the carbonization of TPS played an essential role in the observed high conductivity. The TPS structural change explains the behavior of the HTT-dependent electrical conductivity. That is, the HTT-dependent conductivity is closely related to the evolution of its graphitic structure, as shown in the TEM study and the \u0026pi;-\u0026pi;* shake-up feature. The increase in conductivity from TPS800 to TPS1300 originated from the increase in ordered graphitic structures. Above 1350 \u0026deg;C, the crystal size became too small to produce sufficient electrical conducting paths in the TPS compared to TPS1300. Hence low conductivity was observed in the TPS treated above 1350 \u0026deg;C.\u003c/p\u003e\n\u003cp\u003eTo further investigate the attachment ability of PDA, magnetic textiles were fabricated using Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e powders. The fabrics were obtained by simply mixing the powders in when PDA was embedded in the silk. SEM images and energy dispersive spectroscopy (EDS) elemental mapping in Fig. 4e-h show that Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e particles were well coated onto the silk fiber surface due to PDA. The magnetic property was exhibited by this fabric. We observed an attracting force between the fabric and magnet (Fig. 4i and j, Movie S6). We also fabricated functionalized fabrics with Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e powders (Fig. S28). Although improvement is needed, the Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e-coated TPS thermally treated at 550 \u0026deg;C showed potential for use as a flexible thermoelectric material. Its thermoelectric power was -32.3 \u0026mu;V\u0026middot;K\u003csup\u003e-1\u003c/sup\u003e at 300 K, which is comparable to previous reports for flexible thermoelectric devices fabricated with carbon materials [37-39].\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, embedding PDA into silk and the subsequent polymerization of the dopamine monomers caused the silk fiber to swell. After heat treatment, the cylindrical silk fibers changed to a laminar shape, which was caused by the delamination of \u003cem\u003e\u0026beta;\u003c/em\u003e-crystallites in the silk. Long-range ordered structures with a lattice distance of 3.4 \u0026Aring; formed at a treatment temperature of around 1300 \u0026deg;C. The resulting TPS exhibited super-flexibility and was electrical conducting. This process was also investigated by molecular dynamics calculations, which analyzed the interaction between the dopamine and \u003cem\u003e\u0026beta;\u003c/em\u003e-sheets. The results were well consistent with the experimental results. These results confirm that, by exploiting the attachment ability of PDA and delamination of silk fibers, TPS has potential uses in various applications such as a clothing-based generator, using electromagnetic induction and thermoelectric textiles.\u003c/p\u003e\n"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflicts of interest\u0026nbsp;\u003c/strong\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eH.\u0026ndash;S. J., S. K., and I. P. contributed equally to this work.\u0026nbsp;The authors thank Prof. H. R. Moon, J. S. Kim, and\u0026nbsp;H.-J. Jin for their valuable comments.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003eB.H.K.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ewas supported by the National Research Foundation of Korea (NRF) by the Korea Government (MSIT) (NRF-2020R1A2C4001513). Y.K. was supported by the National Research Foundation of Korea (NRF) by the Korea Government (MSIT) (NRF-2021R1F1A106411113). J.K. was supported by the National Research Foundation of Korea (NRF) by the Korea Government (MSIT) (NRF-2022R1F1A1059616). S.B.C. was supported by the Ministry of Science and ICT, (Project Number: 2023-22030003-00) and Commercialization Promotion Agency for R\u0026amp;D Outcomes (COMPA). R.M. was supported under research grant number UMO-2018/31/B/ST8/02460 from the National Science Centre.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eNovoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, Grigorieva IV, Firsov AA (2004) Electric field effect in atomically thin carbon films. Science 306:666-669. https://doi.org/10.1126/science.1102896\u003c/li\u003e\n\u003cli\u003eZhang Y, Tan Y-W, Stormer HL, Kim P (2005) Experimental observation of the quantum Hall effect and Berry\u0026rsquo;s phase in graphene. Nature 438:201-204. http://doi.org/10.1038/nature04235\u003c/li\u003e\n\u003cli\u003eLi G, Luican A, Lopes dos Santos JMB, Castro Neto AH, Reina A, Kong J, Andrei EY (2010) Observation of Van Hove singularities in twisted graphene layers. 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ACS Appl Energy Mater 3:2556-2564. http://doi.org/10.1021/acsaem.9b02243\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":"advanced-composites-and-hybrid-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"achm","sideBox":"Learn more about [Advanced Composites and Hybrid Materials](https://link.springer.com/journal/42114)","snPcode":"42114","submissionUrl":"https://submission.nature.com/new-submission/42114/3","title":"Advanced Composites and Hybrid Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Commercial silk, Polydopamine, Delamination of silk, Super-flexible electronic textiles","lastPublishedDoi":"10.21203/rs.3.rs-3281213/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3281213/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Exfoliation has been used to obtain 2D materials with attractive properties, like graphene. The layered structure of silk and its structural transition to a pseudo-graphitic structure by heat treatment has attracted scientific interest because of its potential applications. Here we report that intercalating the silk layers with polydopamine (PDA) followed by thermal treatment delaminates the silk fibers. Cylindrical silk fibers with a diameter of 10 μm changed to graphitic ribbon-like structures with widths of approximately 65 nm. This structural transition was systematically investigated using thermally treated PDA-embedded silks at temperatures from 800 to 1450 °C. The graphitic structures start to be observed at 1000 °C, a much lower heat treatment temperature than previous studies using pure silk. Long-range ordered graphitic structures with a lattice distance of 3.4 Å formed most clearly at 1300 °C. ab-initio molecular dynamics calculations confirmed the microscopic origin of the experimental results. This method allows the fabrication of super-flexible, comparable to pure silk, and high-electrically conductive (277.3 S·cm-1) e-textiles. These thermally treated PDA-embedded silks were also functionalized with Fe2O3 and Bi2Te3 powders using the attachment ability of PDA. This work provides evidence that PDA plays a role in delaminating silk fibers and opens the potential for various applications.","manuscriptTitle":"Long-range Ordered Graphitic Structure in Silk Fibers Delaminated using Dopamine and Thermal Treatment for Super-Flexible Electronic Textiles","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-08-29 14:36:05","doi":"10.21203/rs.3.rs-3281213/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2023-09-27T13:05:34+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-09-23T17:11:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"12d5bb0e-83f5-474d-be26-dd1caf12bc3f","date":"2023-09-18T13:47:34+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-09-18T13:42:35+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-09-08T21:57:10+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-08-25T04:19:59+00:00","index":"","fulltext":""},{"type":"submitted","content":"Advanced Composites and Hybrid Materials","date":"2023-08-21T05:59:13+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"advanced-composites-and-hybrid-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"achm","sideBox":"Learn more about [Advanced Composites and Hybrid Materials](https://link.springer.com/journal/42114)","snPcode":"42114","submissionUrl":"https://submission.nature.com/new-submission/42114/3","title":"Advanced Composites and Hybrid Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"13bdb935-3c20-4896-a71c-87ba391bf864","owner":[],"postedDate":"August 29th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-02-26T15:02:29+00:00","versionOfRecord":{"articleIdentity":"rs-3281213","link":"https://doi.org/10.1007/s42114-024-00857-y","journal":{"identity":"advanced-composites-and-hybrid-materials","isVorOnly":false,"title":"Advanced Composites and Hybrid Materials"},"publishedOn":"2024-02-20 15:00:37","publishedOnDateReadable":"February 20th, 2024"},"versionCreatedAt":"2023-08-29 14:36:05","video":"","vorDoi":"10.1007/s42114-024-00857-y","vorDoiUrl":"https://doi.org/10.1007/s42114-024-00857-y","workflowStages":[]},"version":"v1","identity":"rs-3281213","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3281213","identity":"rs-3281213","version":["v1"]},"buildId":"FbvkV6FR0MCFSLy54lSbu","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}