Preparation and Performance Evaluation of Slow-expanding Hydrophobic Polymer Nanomicrospheres

Preparation and Performance Evaluation of Slow-expanding Hydrophobic Polymer Nanomicrospheres | 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 Preparation and Performance Evaluation of Slow-expanding Hydrophobic Polymer Nanomicrospheres Rui Wang, Lei Wang, Zhiqiang Dang, Xiaojuan Lai, Peng Li, Simin Zhou, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6885960/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Aiming to solve the problems of the large particle size, high expansion rate of polymer microspheres currently used in anatomical water-plugging technology. In this study, acrylamide (AM), acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and 4-acrylamido-morpholine (ACMO) were used as the raw materials, and the hydrophobic monomer, hexadecyl dimethyl allyl ammonium chloride (DMAAC-C 16 ), and the cross-linking agent poly(ethylene glycol) 200 diacrylate (PEG200DA). A slow-expanding temperature- and salt-resistant polymer nanomicrospheres (PHM) were prepared by reverse-phase microemulsion polymerization. The PHM structure was characterized using infrared spectroscopy, nuclear magnetic resonance spectroscopy, and scanning electron microscopy, and their properties were analyzed nano-laser particle sizing, and rheometry and employing the filtration factor. Results showed that the average particle size of PHM was 68.69 nm. The swelling multiplicity of PHM microspheres was 4.34 times after four days of dissolution in water at 80°C. The swelling multiplicity after four days of dissolution in mineralized water with a mineralization level of 80,000 mg/L at 25°C was 2.34 times, and the blocking rate was more than 85%. The slow expansion of the synthesized PHM under the high-temperature and high-salt conditions confirmed their good expansion performance. Viscoelasticity test showed that the synthesized PHM had good elasticity and injection properties. Nanomicrospheres Slow expansion Temperature resistance Salt resistance Plugging Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction China’s low-permeability reservoirs are widely distributed, such as carbonate, sandstone, and other reservoirs. Owing to the complex stratigraphic structure and low stratigraphic energy of such reservoirs, extraction from them is difficult, compared with conventional reservoirs, necessitating external energy supply to improve recovery rates [ 1 – 3 ]. Therefore, water injection mining has become a commonly used technology to improve recovery rates; however, the long-term use of this technology leads to the formation of water flow channels, through which most of the injected water is extracted without playing an oil-repulsion role. Hence, a large number of water injection becomes ineffective [ 4 ], declining oil-recovery efficiency dramatically and thereby seriously affecting the economic benefits of oilfield and sustainable development. In response to the above problems, anatomical plugging technology is developed. The water-plugging work is primarily adjusted to mediate the fluid-flow profile in the oil reservoir, reduce the ineffective water circulation during the process of water-driven oil extraction, and improve the recovery rate of crude oil. This technology is mainly used to improve oil recovery by injecting specific chemical plugging agents into the formation, sealing pores and fractures in the formation, and directing water flow to the underdeveloped oil zones [ 5 – 7 ]. At present, the main types of anatomical water-plugging agents are gels, granules, foams, microorganisms, and polymer microspheres [ 8 – 13 ]. Currently, although there are various water-plugging materials that can basically meet the needs of conventional reservoir water plugging, their applicability to low-permeability reservoirs is still limited by many challenges. For example, the particle size of granular plugging agent is difficult to accurately match with the pore space and pore throat of the formation; the application of microbial plugging agent in the complex formation structure and high temperature and high salt environment is also subject to certain limitations [ 14 ]. In addition, the large average particle size of conventional polymer microspheres [ 15 – 17 ], restricts their effectiveness in complex reservoir conditions. To achieve the effective sealing of fine pores in the formation, the use of polyacrylamide-based polymer microspheres has received increased attention. These polymer microspheres have the unique advantage that their average particle size can reach the nanoscale [ 18 – 20 ], overcoming the problem of the large particle size of conventional water-plugging agents. However, the presently studied polyacrylamide-based polymer microspheres have problems such as a considerably high expansion rate and poor transport effect. Utilizing reverse-phase microemulsion polymerization, Yu et al. [ 21 ] synthesized temperature and salt-resistant amphiphilic polyacrylamide microspheres with an average particle size of 50 nm. After aging in brine at 90℃ for seven days, their average particle size increased 12.68 times, reaching 634 nm. Zhou et al. [ 22 ] synthesized double-crosslinked nanopolymer gel (DCNPM-A) microspheres using acrylamide, sodium p-styrenesulfonate, and dimethyldiallylammonium chloride as functional monomers and N,N-methylenebisacrylamide and poly(ethyleneglycol) diacrylate as crosslinking agents. They showed that the maximum swelling multiplicity of their DCNPM-A microspheres reached 13.5 times in one day. When the expansion rate of the microspheres is too fast, it will cause the microspheres to expand during the injection process before they reach the tiny pores deep in the formation, which seriously affects the injection effect. To resolve the above problems, in this paper, on the basis of AM, the temperature and salt resistance of the polymer was improved by introducing AMPS and ACMO, and the stability of the polymer was improved by adding AA. The addition of the hydrophobic monomer DMAAC-C 16 improves the intermolecular forces of the polymer and further improves the polymer's temperature and salt resistance and shear resistance. PEG200DA was also added as a crosslinking agent, providing flexible polymer chains that enhance the elasticity and improve the injection efficiency of the polymer. Ultimately, temperature and salt-resistant polyacrylamide nano–microspheres (PHM) with good swelling-retardation properties were prepared via reverse microemulsion polymerization. 2. Materials and methods 2.1. Materials The raw materials were analytically pure AM (Tianjin Komeo Chemical Reagent Co., Ltd.), analytically pure AA and analytically pure azobisisobutyronitrile (AIBN) (Shanghai Jingma Chemical Science & Technology Co., Ltd.), analytically pure AMPS (Shandong Shouguang Rund Chemical Co., Ltd.), analytically pure ACMO (Boai XinOpen Source Pharmaceutical Co., Ltd.), industrially produced DMAAC-C 16 (Zhangjiagang Renda Chemical Co., Ltd.), analytically pure PEG200DA (Shanghai AiPure Biotechnology Co., Ltd.), industrially produced 3 # white oil (Shaanxi Runtai Chemical Co., Ltd.), analytically pure sorbitan anhydride oleate (Span-80) and polyoxyethylene (20) ether sorbitan anhydride monooleate (Tween-80) (Maoming Branch of China Petrochemical), analytically pure N,N-methylene bisacrylamide (MBA) (Tianjin Huasheng Chemical Reagent Co., Ltd.), analytically pure anhydrous ethanol (Shandong Noor Chemical Co., Ltd.), analytically pure tert-butyl hydroperoxide (TBHP) (Hubei Keward Chemical Co. Ltd.), analytically pure sodium metabisulfite (Na 2 S 2 O 5 ) (Shanghai Yuanye Biotechnology Co., Ltd.), analytically pure isotridecanol polyoxyethylene ether (TO-7) (Guangdong Wengjiang Chemical Reagent Co., Ltd.), and analytically pure sodium chloride (NaCl), magnesium chloride hexahydrate (MgCl 2 ·6H 2 O), calcium chloride (CaCl 2 ), and sodium hydroxide (NaOH) (Sinopharm Group Chemical Reagent Co., Ltd.). Distilled water was prepared in the laboratory. 2.2. Equipment The samples were characterized using a Fourier transform infrared (FTIR) spectrometer (AIM-8800, Shimadzu), nuclear magnetic resonance ( 1 H NMR) spectrometer (AVANCE NEO 600MHz), field-emission scanning electron microscope (Verios 460, FEI Corporation Bruker, Switzerland), thermogravimetric analyzer (TGA-Q500, USA), a nano-laser particle sizer (Malvern Instruments, UK), and a MARS60 rotational rheometer (Thermo Electron; Karlsruhe, Germany). 2.3. Synthesis of polyacrylamide microspheres A total of 171.2 g 3 # white oil, 20.5 g Tween-80, 53.8 g Span-80, and 0.3 g AIBN was added to a 500 ml beaker and stirred well using a magnetic stirrer until a light-yellow transparent liquid was obtained. This liquid was transferred to a 1000 mL three-necked flask and set aside. Next, 96.7 g AM, 5.8 g AMPS, 7.6 g AA, 2.5 g ACMO, 2.1 g DMAAC-C 16 , and 0.2 g PEG200DA were weighed in a 500 ml beaker. After adding 140.5 ml deionized water, the mixture was stirred well with a magnetic stirrer until the monomer had dissolved. The pH of the aqueous phase was then adjusted to 6–7 with the addition of a NaOH solution (30% mass concentration), and the mixture was transferred to a three-necked flask. After emulsification by N 2 under stirring for 30 min in the three-necked flask, 4 mL TBHP solution (1% mass concentration) was added, and the mixture was stirred for 10 min. Next, 3.7 mL Na 2 S 2 O 5 solution (1% mass concentration) was added, and reaction continued for 1.5 h under N 2 conditions. A certain amount of the TO-7 phase transfer agent was added to this solution, followed by stirring well to obtain a yellow translucent liquid (the PHM emulsion). An appropriate amount of the product was collected and washed with anhydrous ethanol, extracted through filtration, and placed in a 75℃ drying oven for 4 h, obtaining a solid powder of PHM. Conventional PCM without hydrophobic monomers were synthesized through parallel processes using MBA as the crosslinking agent. The synthesis routes of PHM and PCM microspheres are shown in Fig. 1 (a), (b). 2.4. Characterization and performance testing 2.4.1. Fourier transform infrared spectroscopy The washed, filtered and dried PHM and PCM sample powders were mixed with potassium bromide (1:100) and pressed. Their structures were characterized by FTIR in the scanning wavelength range 4000–500 cm –1 . 2.4.2. Nuclear magnetic resonance hydrogen spectroscopy The PHM were further characterized using 1 H NMR spectroscopy in deuterium oxide (D 2 O) solvent at a test frequency of 600 MHz. 2.4.3. Scanning electron microscopy The microsphere samples were dried, processed, and sprayed with gold in preparation for microstructural characterization using scanning electron microscopy (SEM). 2.4.4. Thermogravimetric analysis The thermal stabilities of the PHM and PCM were evaluated using a thermogravimetric analyzer. The temperature was increased from 25℃ to 600℃ at a ramp rate of 10℃/min under a N 2 flow (40 mL/min). The thermal decomposition rates of the microspheres were observed under nitrogen-ventilated conditions. 2.4.5. Particle size testing The PHM and PCM (0.5% mass concentration) were dispersed in 3 # white oil at room temperature. The dispersions were stirred for 10 min with a magnetic stirrer and then ultrasonicated for 5 min in an ultrasonic cleaner. The initial average particle sizes of the PHM and PCM were determined using a nano-laser particle sizer. 2.4.6. Tests of expansion performance (1) Water absorption and expansion A total of 0.2 g of each PHM and PCM microsphere sample powder was dissolved in 99.8 g deionized water, and the solutions were placed in a constant-temperature oven set to different temperatures (25℃, 40℃, 60℃, and 80℃). Samples were collected at different times and ultrasonicated to ensure the homogenous dispersion of microspheres. A small amount of the solution was inserted into the nano-laser particle sizing instrument for average particle size measurements. 2. Salt resistance testing A total of 0.2 g each PHM and PCM microsphere sample powder was dissolved in 99.8 g brine at different mineralization levels (5000, 10000, 20000, 40000, and 80000 mg/L). Samples were collected at different times, and their average particle sizes were measured with the nano-laser particle sizer. The expansion multiplicities of the samples prepared at different mineralization levels and temperatures were calculated based on the change in the average particle size before and after microsphere expansion. The expansion factor Q of the microspheres was calculated as \(\:Q=\frac{{D}_{2}-{D}_{1}}{{D}_{1}}\times\:100\%\) (1–1) where D 1 and D 2 are the average particle sizes before and after expansion, respectively (both in nm). 2.4.7. Viscoelasticity testing using rheometry Aqueous solutions of PHM and PCM with mass concentrations of 0.2% and 0.4%, respectively, were prepared and their energy storage moduli (G′) and loss moduli (G′′) were determined with respect to scanning frequency and stress. 2.4.8. Blocking performance testing A total of 1.0 g PHM microsphere sample powder was added to a 1500 mL beaker containing 999.0 g of brine at a specified mineralization level. The mixture was stirred for 20 min with a magnetic stirrer and a 1000 mL microsphere dispersion with a mass concentration of 0.1% was filtered through a 0.2 µm membrane in the filtration factor tester. After adding 500 mL deionized water, the pressure was tested at 0.2 MPa. The volume of filtrate was measured for 3 min and recorded as V 1 . Next, a 0.2 µm filter membrane was placed in the filtration factor tester, 500 mL of the microsphere dispersion was added and the volume of filtrate was measured for 3 min at 0.2 MPa. The result was recorded as V 2 . The blocking rate W 1 (%) was calculated as \(\:{W}_{1}=\frac{{V}_{1}-{V}_{2}}{{V}_{1}}\times\:100\%\) (1–2) where V 1 and V 2 are the filtrate volumes of the microsphere dispersion in water and brine, respectively (both in mL). 3. Results and discussion 3.1. Fourier transform infrared spectroscopy Figure 2 shows the FTIR spectra of the PCM and PHM. The infrared spectrograms of both microspheres show the vibrational absorption peaks of the amino-group N–H at 3333 cm –1 and carboxyl-group O–H of AA at 3189 cm –1 . The peaks at 2921 and 2850 cm –1 are assigned to the C–H stretching vibrations of the methylene and methyl groups, respectively. The strong absorption peaks observed at 1673 and 1449 cm –1 are related to the vibrational absorption peaks of C = O and bending vibrational absorption peak of C–H in methylene, respectively, and the peak at 1316 cm –1 belongs to C–N stretching vibrations in ACMO. The peaks at 1190 and 1039 cm –1 correspond to the stretching vibrations of S = O and S–O, respectively, in the sulfonic acid moiety in AMPS. The peak at 1112 cm –1 is assigned to the stretching vibrations of C–O–C in ACMO. The peak at 768 cm –1 in the spectrogram of PHM, which is absent in the PCM spectrogram, corresponds to the bending vibrations of –CH 2 – in the long-chain alkyl group in the hydrophobic monomer DMAAC-C 16 . The infrared spectra of both microspheres also show the absorption peaks of their monomers, confirming the successful synthesis of the target products—PCM and PHM. 3.2. Nuclear magnetic spectrographic analysis Figure 3 shows the 1 H NMR spectrum of PHM. The strong peak at δ = 4.79 ppm is the D 2 O solvent peak. The proton peaks at δ = 1.60 and 2.16 (labeled a and b, respectively, in Fig. 3 ) correspond to the –CH 2 – and –CH– groups on the main chain of the polymer, respectively. The peaks at δ = 3.21 and 3.84 (labeled c and d, respectively) correspond to the –CH 2 – group on the morpholine ring of ACMO. The peaks at δ = 1.40 (e) and δ = 3.62 (f) belong to the –CH 3 group in AMPS and–CH 2 – group in ACMO, respectively. The peaks at δ = 2.32 (g), δ = 1.05 (h), δ = 1.30 (i), and δ = 0.91(j) are assigned to the –CH 2 – group in DMAAC-C 16 , –CH 3 group attached to N + in DMAAC-C 16 , –CH 2 – group in the long-chain alkyl group attached to N + in DMAAC-C 16 , and –CH 3 group in the long-chain alkyl group in DMAAC-C 16 , respectively. The protons of all five monomers, AM, AA, AMPS, ACMO, and DMAAC-C 16 , are correctly attributed, confirming the synthesis of the target product PHM. 3.3. Scanning electron microscopy Figure 4 shows the SEM images of PHM (a, b) and PCM (c, d). The microscopic surface of PHM microspheres was smooth with clear edges and complete sphericity. The surface of PCM microspheres was rough, showing granular or concave structure and agglomeration. The introduction of the hydrophobic monomer DMAAC-C 16 enhanced the hydrophobic association between the polymer chains. During polymerization or microsphere formation, the hydrophobic groups tend to aggregate with each other through van der Waals forces or hydrophobic effects, forming dense hydrophobic microregions. This internal ordering reduces the random curling of molecular chains, resulting in a more uniform and smooth surface structure. In addition, the introduction of DMAAC-C 16 with strong ionization groups into the PHM microspheres increased the surface charge of the PHM microspheres, leading to the fact that the PHM microspheres could inhibit inter-microsphere agglomeration through electrostatic repulsion, resulting in an increase in the dispersion of the PHM microspheres and an increase in the independent sphere-forming ability of individual microspheres, and thus the PHM microspheres had a smoother surface and a more intact sphericity than the PCM microspheres. 3.4. Thermogravimetric analysis The thermal stabilities of the PCM and PHM were evaluated from the thermogravimetric analysis plots over the temperature range of 25°C–600°C (see Fig. 5 ). The thermal decomposition curves of the PCM and PHM are divided into three main stages. During the first stage, the PCM and PHM lose 8.29% and 5.97% of their weight, respectively, mainly because heating volatized the water and small molecules in the polymer microspheres. The weight losses during the second stage, 22.69% and 19.82% from the PCM and PHM, respectively, are attributed to volatilization of the organic matter in the polymer microspheres, along with fracture and decomposition of the amide groups as the heating continued. Eventually, the remaining organic matter in the polymers volatilized and some of the branched chains of the polymer microspheres decompose and detach from the main chains. At 500°C, the remaining amounts of PCM and PHM microspheres are 11.62% and 22.15%, respectively. Introducing the hydrophobic monomer DMAAC-C 16 strengthens the intermolecular forces of PHM and improves the thermal stability of the molecular chains. Therefore, PHM are more thermally stable than PCM. 3.5. Particle size analysis Figure 6 (a), (b) shows the initial mean particle size distributions of PHM and PCM obtained by nano-laser particle sizer, respectively. The average particle sizes of PHM and PCM are 68.69 and 146.1 nm, respectively. PHM are smaller and more homogenous and exhibit a narrower particle size distribution (37.56–125.6 nm) than PCM. The higher homogeneity of PHM is attributed to the use of the hydrophobic DMAAC-C 16 monomer, which enhances the polymer intermolecular chains association by strengthening the bonding effect between polymer molecular chains. The more compact and stable spatial network structure formed inside microspheres reduces the particle size of PHM. 3.6. Expansion performance testing 3.6.1. Effect of time on swelling properties The average particle sizes of the PCM and PHM (0.2% mass concentration) were monitored at different swelling times in deionized water. The results are shown in Fig. 7 . The initial average particle sizes of PHM and PCM in the aqueous phase are 164.67 and 205.34 nm, respectively. After four days, the average PHM and PCM particle sizes increase 2.86 and 5.63 times, reaching 471.71 and 1156.39 nm, respectively. Compared with PCM, the expansion rate of PHM is lower in four days, indicating that PHM are more likely to maintain their original morphology and transportability during the injection process and will more easily penetrate small pore throats and orifices in the formation. This improves the efficiency of injection and reduces the energy consumption and cost of the injection process. In addition, the low expansion rate can avoid the premature expansion of PHM and plugging of the near-well zone, which can adjust the permeability of the formation more uniformly and increase the wave volume, thereby improving the recovery rate. 3.6.2. Effect of temperature on expansion properties Figure 8 plots the average particle sizes of the PCM and PHM (0.2% mass concentration) in deionized water as functions of swelling time at 40℃, 60℃, and 80℃. At any given temperature, the expansions of PHM and PCM are initially fast and then slowed with the extension of time at the same temperature for four days. After four days of swelling at 40℃, the average particle sizes of PHM and PCM are 553.28 and 1202.39 nm, swelling 3.36 and 5.86 times, respectively, compared with their initial average particle sizes in the aqueous phase. At 80°C, the swelling multiplicities of PHM and PCM increase to 4.34 and 6.69 times, and their average particle sizes are 714.76 and 1374.71 nm, respectively. Compared with PCM, with an increase in temperature, the expansion rate of PHM at different temperatures is smaller. At all temperatures, the average particle sizes of PHM remain within the nanoscale after four days of expansion, indicating that a high temperature has a little effect on the ability of PHM to be transported through the stratum. This performance is mainly attributable to the introduction of the polymer molecular chains of ACMO, which contains a rigid heterocyclic structure that improves the rigidity of the polymer molecular chains and inhibits its thermal movement at high temperatures, thereby reducing the thermal degradation of chain segments. Moreover, N and O atoms in ACMO can form hydrogen bonds with water molecules and polymer chains to enhance intermolecular forces and improve polymer structure stability, making the polymer molecular chains not easy to break at high temperatures. The introduction of the hydrophobic monomer DMAAC-C 16 further improves the intermolecular forces and temperature-resistant properties of PHM. 3.6.3. Effect of mineralization on swelling properties The variation in the average particle sizes of PCM and PHM microsphere solutions (0.2% mass concentration) in water with different mineralization levels for four days at 25℃ is shown in Fig. 9 . The average particle sizes of PCM and PHM at the same salt concentration increase with time and decrease with increasing mineralization levels, indicating that the higher the mineralization, the slower the expansion of microspheres. After four days of dissolution at a mineralization level of 80,000 mg/L, the average particle sizes of PHM and PCM are 214.52 and 642.72 nm, expansion by 2.34 and 5.37 times, respectively. Strongly polar sulfonic acid groups in AMPS molecule enhance the tolerance of polymer microspheres to ions such as Ca 2+ and Mg 2+ , providing the polymers with excellent hydration ability and decreasing their susceptibility to bilayer compression by salt ions in the highly mineralized environment. Therefore, the swelling and stability of PHM are preserved in brine, and their salt resistance is improved. Compared with PCM, PHM expand more slowly under the high-salt environment. This is because with increasing mineralization, the intermolecular bonding of PHM is enhanced, making the spatial network structure of PHM more compact. Thus, compared with PCM microspheres, PHM microspheres have good swelling retardation and better salt resistance. 3.7. Blocking performance The variation in the blocking rates of PHM microsphere solutions (0.1% mass concentration) in aqueous solutions with different mineralization levels at different times is shown in Fig. 10 . The blocking performance of PHM is affected by a combination of the swelling time and mineralization level. With the prolongation of the swelling time, the average particle size and blocking rate of PHM increase continuously in four days, and the blocking rate remains basically unchanged thereafter. Meanwhile, the blocking rate of PHM decreases with increasing the mineralization degree. This is mainly because the ionic strength of the solution increases at high mineralization levels, compressing the double layer formed on the microsphere surface and affecting the swelling behavior of the polymer microspheres. The test results show that the blocking rate of PHM at different mineralization levels is greater than 80%. This is attributed to the introduction of AMPS possessing a strong polar sulfonic acid group to the polymer molecular chains, improving the hydrophilicity of the microspheres. The formation of a stable, hydrated ionic layer attenuates the charge-shielding effect of salt ions, thereby improving the salt resistances of the polymers. In addition, the presence of the hydrophobic monomer DMAAC-C 16 and crosslinking agent PEG200DA endows the polymer microspheres with good elasticity and stability. Elastic deformation enables the more tight packing of the microspheres within the pore spaces of the stratum during the process of blocking, improving the blocking effect of the fine pore space in the stratum. 3.8. Viscoelasticity evaluation Figure 11 (a) plots the energy storage moduli G′ and loss moduli G′′ of the PHM and PCM at different mass concentrations (0.2% and 0.4%) in deionized water as a function of stress. The frequency dependencies of the same solutions are shown in Fig. 11 (b). As shown in Fig. 11 (a), PHM display higher G′ and G′′ than PCM at the same concentration; moreover, G′ and G′′ increase with increasing PHM concentration. At a mass concentration of 0.2%, the modulus–stress curves of PHM plateau in the low-stress range, and with an increase in stress, G′ and G′′ gradually decrease. The plateau disappears when G′ < G′′ due to the fact that the associative structure formed between the molecular chains of the polymers is destroyed under stress, phenomenon of shear dilution occurs, and viscoelasticity of the solution decreases. PHM microspheres with a mass concentration of 0.4% showed a more pronounced linear plateau with G′ > G′′ over the stress scan range, with the microsphere solution being more elastic than viscous. As evidenced in Fig. 11 (b), the G′ and G′′ moduli of PCM and PHM increase with increasing scanning frequency. The PHM solutions with mass concentrations of 0.2% and 0.4% are more elastic, and their G′ exceeds G′′. At the same concentration, PHM yield a higher G′ than PCM, indicating their higher elasticity . Figure 12 shows a schematic of the shear-resistance mechanism of PHM. A conventional crosslinker MBA has a small molecular weight and undergoes dense crosslinking, mainly with rigid chain segments, such as –C–C– and –C–N–, which are prone to breakage under shear forces. Compared with MBA, PEG200DA molecules are connected via –C–O– bonds present between main polymer chains. As molecular chains can rotate around the axis of oxygen atom and can be stretched or compressed, the molecular chains structure is highly flexible; accordingly, PEG200DA improves the elasticity of PHM. In addition, as a hydrophobic monomer, DMAAC-C 16 increases intermolecular association among PHM, and the formation of a reticular structure improves the stability of PHM. Therefore, when PHM are subjected to stratigraphic shear, the slip and fracture of chain segments cannot occur easily, exhibiting good shear resistance. 3.9. Blocking mechanism The blocking mechanism of PCM and PHM is shown in Fig. 13 . As shown in Fig. 13 (a), the PCM expand rapidly and swell before reaching the depth of the formation, resulting in a poor injection effect and a deteriorated blocking effect in the deep formation. As shown in Fig. 13 (b), The slowly expanding PHM can be transported to deeper depths in the formation and exhibit high injection performance. In addition, the crosslinking agent PEG200DA and hydrophobic monomer DMAAC-C 16 contribute elasticity and anti-shear properties to the PHM. When subjected to formation shear and extrusion during injection into the stratum, the PHM can deform sufficiently to pass through the small pores and throats in the stratum, effective blocking the pore spaces in the deep stratum. 4. Conclusion (1) A temperature and salt-resistant PHM microsphere with good swelling retardation properties was synthesized by reversed-phase microemulsion polymerization using AM, AA, AMPS, ACMO, and DMAAC-C 16 as the polymerization monomers, PEG200DA as the cross-linking agent. TBHP and Na 2 S 2 O 5 as the initiator. FTIR and 1 H NMR spectroscopies confirmed the structure of PHM, reveling that the target products were successfully synthesized. Thermogravimetric analysis showed that PHM had good thermal stability. (2) The average particle size of PHM was 68.69 nm. During swelling performance test in water, PHM swelled to 2.32 and 2.86 times their initial size after two and four days, respectively, at room temperature. After four days in an aqueous solution at 40°C and 80°C, the expansion multiplicities of PHM were 3.36, 4.34 times, respectively. After four days in mineralized water (80,000 mg/L) at 25°C, the expansion multiplicity was 2.34 times. The synthesized PHM showed good temperature and salt resistances and slow expansion properties. Moreover, the blocking rate of a PHM solution tended to be stable and greater than 85% after four days at different mineralization levels, indicating that PHM possessed strong blocking ability. Finally, viscoelasticity test confirmed the good elasticity and shear-resistance properties of PHM, conducive to improving their injection effect. Declarations Author Contributions Rui Wang: Conceptualization, Methodology, Formal analysis, Writing- original draft; Lei Wang: Funding acquisition; Zhiqiang Dang: Investigation and project administration; Peng Li: Software; Xiaojuan Lai: Supervision; Simin Zhou: Validation and visualization; Yuejing Lu: Data curation; Xiaomei Jiang: Review and editing. Funding This research was financially supported by the Qin-Chuangyuan "Scientist and Engineer" Team Construction Project (2024QCY-KXJ-052), Key R&D Program of Shaanxi Province (2024GX-YBXM-393), Key scientific research project of Shaanxi Provincial Department of Education (22JT002) and the Youth Innovation Team Project of Shaanxi Universities(24JP022). Data Availability Statement All of the material is owned by the authors and no permissions are required. 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Tang, W. Kang, B. Zhou, Y. Gao, C. Cao, S. Guo, M. W. Iqbal, H. Yang. Characteristics of composite microspheres for in-depth profile control in oilfields and the effects of polymerizable silica nanoparticles [J]. Powder Technology, 2020, 359 205-215. S. Zhou, Z. Li, K. Gao, J. Zhou, Y. Zhou, D. Yang. Preparation and performance of graphene oxide-polyacrylamide based nanoscale microsphere emulsion for profile control[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2023, 671. Z. Li, T. Zhao, W. Lv, B. Ma, Q. Hu, X. Ma, Z. Luo, M. Zhang, Z. Yu, D. Yang. Nanoscale Polyacrylamide Copolymer/Silica Hydrogel Microspheres with High Compressive Strength and Satisfactory Dispersion Stability for Efficient Profile Control and Plugging[J]. INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 2021, 60 (28): 10193-10202. S. Wang, Z. Tang, J. Qu, T. Wu, Y. Liu, J. Wang, X. Liu, Y. Ju, F. Liu. 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Supplementary Files Tableofcontents.pdf Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 16 Jul, 2025 Reviews received at journal 16 Jul, 2025 Reviews received at journal 13 Jul, 2025 Reviews received at journal 12 Jul, 2025 Reviewers agreed at journal 06 Jul, 2025 Reviewers agreed at journal 04 Jul, 2025 Reviewers agreed at journal 03 Jul, 2025 Reviewers invited by journal 02 Jul, 2025 Editor assigned by journal 16 Jun, 2025 Submission checks completed at journal 16 Jun, 2025 First submitted to journal 13 Jun, 2025 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-6885960","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":479953549,"identity":"fecbb5fa-865d-40b1-a2ee-98feda8e003c","order_by":0,"name":"Rui Wang","email":"","orcid":"","institution":"Shaanxi Key Laboratory of Chemical Additives for Light Industry, Shaanxi University of Science \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Rui","middleName":"","lastName":"Wang","suffix":""},{"id":479953553,"identity":"c45eecee-b8e6-4d3f-ba8b-931d17bcfe91","order_by":1,"name":"Lei Wang","email":"","orcid":"","institution":"Shaanxi Key Laboratory of Chemical Additives for Light Industry, Shaanxi University of Science \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Lei","middleName":"","lastName":"Wang","suffix":""},{"id":479953555,"identity":"ebe8a9be-d566-4422-b6ea-ddb8fc4fdd20","order_by":2,"name":"Zhiqiang Dang","email":"","orcid":"","institution":"Shaanxi Key Laboratory of Chemical Additives for Light Industry, Shaanxi University of Science \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Zhiqiang","middleName":"","lastName":"Dang","suffix":""},{"id":479953557,"identity":"efa371ea-948d-404e-9da8-19ff2a50755a","order_by":3,"name":"Xiaojuan Lai","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAw0lEQVRIiWNgGAWjYBACefnzHx9IVNjIsbG3HyBOi+EMBmMDizNpxnw8ZxKItOYGg5lEZcuhxHkSDgbE6WCc3ZBscLPhQHqbBEMCw4+KbYS1sMscOPhw5o47uW3SjQcYe87cJsKWhsRmY8kzz3LbZA4kMDO2EaGF4UAym/TftsPpbBIJBkRquZHGJiHZdjiBeC2GPWeYDSTOpBm2AQP5IFF+kWfvYQRFpbx8e/vBBz8qiHEYMjhAovpRMApGwSgYBbgAAO+wQIzOUzJ1AAAAAElFTkSuQmCC","orcid":"","institution":"Shaanxi Agricultural Products Processing Technology Research Institute","correspondingAuthor":true,"prefix":"","firstName":"Xiaojuan","middleName":"","lastName":"Lai","suffix":""},{"id":479953559,"identity":"8b493022-bd7f-465f-a203-93370653bba9","order_by":4,"name":"Peng Li","email":"","orcid":"","institution":"Shaanxi Key Laboratory of Chemical Additives for Light Industry, Shaanxi University of Science \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Peng","middleName":"","lastName":"Li","suffix":""},{"id":479953562,"identity":"7c2a4e16-85bb-4889-95bc-f807ea7653c6","order_by":5,"name":"Simin Zhou","email":"","orcid":"","institution":"Research Institute of Oil \u0026 Gas Technology, Qinghai Oilfield","correspondingAuthor":false,"prefix":"","firstName":"Simin","middleName":"","lastName":"Zhou","suffix":""},{"id":479953563,"identity":"877f9822-f003-4d33-aa55-448bbb248291","order_by":6,"name":"Yuejing Lu","email":"","orcid":"","institution":"Shaanxi Key Laboratory of Chemical Additives for Light Industry, Shaanxi University of Science \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Yuejing","middleName":"","lastName":"Lu","suffix":""},{"id":479953566,"identity":"1aa8b5be-a531-4300-9645-30d0386b22d3","order_by":7,"name":"Xiaomei Jiang","email":"","orcid":"","institution":"Research Institute of Oil \u0026 Gas Technology, Qinghai Oilfield","correspondingAuthor":false,"prefix":"","firstName":"Xiaomei","middleName":"","lastName":"Jiang","suffix":""}],"badges":[],"createdAt":"2025-06-13 07:53:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6885960/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6885960/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86029776,"identity":"d20df436-c603-451c-a7b5-0a3a43cd5a95","added_by":"auto","created_at":"2025-07-04 14:06:40","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":241481,"visible":true,"origin":"","legend":"\u003cp\u003eSynthesis route of PHM (a) and PCM (b)\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/58a490bbc09c6158dd1f0012.png"},{"id":86030625,"identity":"2cb8614b-bba9-4c34-b147-c38927189802","added_by":"auto","created_at":"2025-07-04 14:14:40","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":61987,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of PCM and PHM microspheres\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/9c4db09a2f681ccd8a1c20c6.png"},{"id":86029778,"identity":"874318cb-d075-4d52-80ff-60ff974b3472","added_by":"auto","created_at":"2025-07-04 14:06:40","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":46758,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR hydrogen spectra of PHM microspheres\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/ce0e5f66c99b5289dec77680.png"},{"id":86030627,"identity":"62a62302-e8bc-40d7-8708-ca667714e875","added_by":"auto","created_at":"2025-07-04 14:14:40","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1025904,"visible":true,"origin":"","legend":"\u003cp\u003e(a), (b) SEM images of PCM; (c), (d) SEM images of PCM\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/6ce6331b23a1585bfd3a73ae.png"},{"id":86030965,"identity":"ec8d62de-94d2-4f29-939e-98f25c684e6d","added_by":"auto","created_at":"2025-07-04 14:22:40","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":60582,"visible":true,"origin":"","legend":"\u003cp\u003eThermogravimetric curves of PCM and PHM\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/b439d61b06758e862e852f06.png"},{"id":86030629,"identity":"3fdf5dfc-5bcf-431d-b658-6086202730be","added_by":"auto","created_at":"2025-07-04 14:14:40","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":72310,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Initial particle size distributions of PHM; (b) Initial particle size distributions of PCM\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/22ced4f3ae39881b4bdf0247.png"},{"id":86029787,"identity":"e9eaf2d8-d020-410b-8fcd-d0c92567dc30","added_by":"auto","created_at":"2025-07-04 14:06:40","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":44032,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of average particle size of PCM and PHM microspheres at different times\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/d26308ae91f282ac506d4909.png"},{"id":86030967,"identity":"3ab39807-1e87-4a19-9100-c8a0cd652242","added_by":"auto","created_at":"2025-07-04 14:22:40","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":73595,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of average particle size of PCM and PHM microspheres at different temperatures\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/f562f93107aa0b6c82ec21a7.png"},{"id":86029786,"identity":"4c4491d9-9889-4b57-a52d-78fa387581d0","added_by":"auto","created_at":"2025-07-04 14:06:40","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":120477,"visible":true,"origin":"","legend":"\u003cp\u003eTemporal changes in average particle sizes of PCM and PHM in water with different mineral concentrations\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/c33ceb71cd9f1ad9603d1828.png"},{"id":86029794,"identity":"6b1a2665-86f5-4bb5-917f-e1c5be7f077d","added_by":"auto","created_at":"2025-07-04 14:06:40","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":76476,"visible":true,"origin":"","legend":"\u003cp\u003eTemporal changes in the blocking rate of PHMs in water with different mineralization levels\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/562c56da9188770a43aaea45.png"},{"id":86029799,"identity":"18618e23-99ee-42a8-b018-10b17bc5f95c","added_by":"auto","created_at":"2025-07-04 14:06:40","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":161721,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Energy storage moduli \u003cem\u003eG\u003c/em\u003e′ and loss moduli \u003cem\u003eG\u003c/em\u003e′′ of PCMs and PHMs (at mass concentrations of 0.2% and 0.4%) in aqueous solutions as functions of stress; (b) Energy storage moduli\u003cem\u003e G\u003c/em\u003e′ and loss moduli \u003cem\u003eG\u003c/em\u003e′′ of PCMs and PHMs (at mass concentrations of 0.2% and 0.4%) as a function of scan frequency\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/61d22753f3763155a21b3fb2.png"},{"id":86029816,"identity":"a3c74a72-1394-4d91-a6f9-3f74d5437c57","added_by":"auto","created_at":"2025-07-04 14:06:41","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":266359,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of the shear-resistance mechanism of PHM\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/a2b95c84c657849503db31ca.png"},{"id":86029804,"identity":"fa4b4904-45f6-4246-aa12-b042c969e433","added_by":"auto","created_at":"2025-07-04 14:06:41","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":590132,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic of the blocking mechanisms of PCM; (b) Schematic of the blocking mechanisms of PHM\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/51cb991c300e9237843376ff.png"},{"id":86032406,"identity":"1f767a10-9370-45f0-8d02-5dc876395894","added_by":"auto","created_at":"2025-07-04 14:38:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4058000,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/9ddc03ec-92f5-4291-8800-0c820b09e483.pdf"},{"id":86029779,"identity":"77ff1c81-8745-4119-9e5e-1619917e1706","added_by":"auto","created_at":"2025-07-04 14:06:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":428267,"visible":true,"origin":"","legend":"","description":"","filename":"Tableofcontents.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6885960/v1/9f33d999205ca3823f90d360.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Preparation and Performance Evaluation of Slow-expanding Hydrophobic Polymer Nanomicrospheres","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eChina\u0026rsquo;s low-permeability reservoirs are widely distributed, such as carbonate, sandstone, and other reservoirs. Owing to the complex stratigraphic structure and low stratigraphic energy of such reservoirs, extraction from them is difficult, compared with conventional reservoirs, necessitating external energy supply to improve recovery rates [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Therefore, water injection mining has become a commonly used technology to improve recovery rates; however, the long-term use of this technology leads to the formation of water flow channels, through which most of the injected water is extracted without playing an oil-repulsion role. Hence, a large number of water injection becomes ineffective [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], declining oil-recovery efficiency dramatically and thereby seriously affecting the economic benefits of oilfield and sustainable development.\u003c/p\u003e \u003cp\u003eIn response to the above problems, anatomical plugging technology is developed. The water-plugging work is primarily adjusted to mediate the fluid-flow profile in the oil reservoir, reduce the ineffective water circulation during the process of water-driven oil extraction, and improve the recovery rate of crude oil. This technology is mainly used to improve oil recovery by injecting specific chemical plugging agents into the formation, sealing pores and fractures in the formation, and directing water flow to the underdeveloped oil zones [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. At present, the main types of anatomical water-plugging agents are gels, granules, foams, microorganisms, and polymer microspheres [\u003cspan additionalcitationids=\"CR9 CR10 CR11 CR12\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Currently, although there are various water-plugging materials that can basically meet the needs of conventional reservoir water plugging, their applicability to low-permeability reservoirs is still limited by many challenges. For example, the particle size of granular plugging agent is difficult to accurately match with the pore space and pore throat of the formation; the application of microbial plugging agent in the complex formation structure and high temperature and high salt environment is also subject to certain limitations [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. In addition, the large average particle size of conventional polymer microspheres [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], restricts their effectiveness in complex reservoir conditions. To achieve the effective sealing of fine pores in the formation, the use of polyacrylamide-based polymer microspheres has received increased attention. These polymer microspheres have the unique advantage that their average particle size can reach the nanoscale [\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], overcoming the problem of the large particle size of conventional water-plugging agents. However, the presently studied polyacrylamide-based polymer microspheres have problems such as a considerably high expansion rate and poor transport effect. Utilizing reverse-phase microemulsion polymerization, Yu et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] synthesized temperature and salt-resistant amphiphilic polyacrylamide microspheres with an average particle size of 50 nm. After aging in brine at 90℃ for seven days, their average particle size increased 12.68 times, reaching 634 nm. Zhou et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] synthesized double-crosslinked nanopolymer gel (DCNPM-A) microspheres using acrylamide, sodium p-styrenesulfonate, and dimethyldiallylammonium chloride as functional monomers and N,N-methylenebisacrylamide and poly(ethyleneglycol) diacrylate as crosslinking agents. They showed that the maximum swelling multiplicity of their DCNPM-A microspheres reached 13.5 times in one day. When the expansion rate of the microspheres is too fast, it will cause the microspheres to expand during the injection process before they reach the tiny pores deep in the formation, which seriously affects the injection effect.\u003c/p\u003e \u003cp\u003eTo resolve the above problems, in this paper, on the basis of AM, the temperature and salt resistance of the polymer was improved by introducing AMPS and ACMO, and the stability of the polymer was improved by adding AA. The addition of the hydrophobic monomer DMAAC-C\u003csub\u003e16\u003c/sub\u003e improves the intermolecular forces of the polymer and further improves the polymer's temperature and salt resistance and shear resistance. PEG200DA was also added as a crosslinking agent, providing flexible polymer chains that enhance the elasticity and improve the injection efficiency of the polymer. Ultimately, temperature and salt-resistant polyacrylamide nano\u0026ndash;microspheres (PHM) with good swelling-retardation properties were prepared via reverse microemulsion polymerization.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eThe raw materials were analytically pure AM (Tianjin Komeo Chemical Reagent Co., Ltd.), analytically pure AA and analytically pure azobisisobutyronitrile (AIBN) (Shanghai Jingma Chemical Science \u0026amp; Technology Co., Ltd.), analytically pure AMPS (Shandong Shouguang Rund Chemical Co., Ltd.), analytically pure ACMO (Boai XinOpen Source Pharmaceutical Co., Ltd.), industrially produced DMAAC-C\u003csub\u003e16\u003c/sub\u003e (Zhangjiagang Renda Chemical Co., Ltd.), analytically pure PEG200DA (Shanghai AiPure Biotechnology Co., Ltd.), industrially produced 3\u003csup\u003e#\u003c/sup\u003e white oil (Shaanxi Runtai Chemical Co., Ltd.), analytically pure sorbitan anhydride oleate (Span-80) and polyoxyethylene (20) ether sorbitan anhydride monooleate (Tween-80) (Maoming Branch of China Petrochemical), analytically pure N,N-methylene bisacrylamide (MBA) (Tianjin Huasheng Chemical Reagent Co., Ltd.), analytically pure anhydrous ethanol (Shandong Noor Chemical Co., Ltd.), analytically pure tert-butyl hydroperoxide (TBHP) (Hubei Keward Chemical Co. Ltd.), analytically pure sodium metabisulfite (Na\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e) (Shanghai Yuanye Biotechnology Co., Ltd.), analytically pure isotridecanol polyoxyethylene ether (TO-7) (Guangdong Wengjiang Chemical Reagent Co., Ltd.), and analytically pure sodium chloride (NaCl), magnesium chloride hexahydrate (MgCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), calcium chloride (CaCl\u003csub\u003e2\u003c/sub\u003e), and sodium hydroxide (NaOH) (Sinopharm Group Chemical Reagent Co., Ltd.). Distilled water was prepared in the laboratory.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Equipment\u003c/h2\u003e \u003cp\u003eThe samples were characterized using a Fourier transform infrared (FTIR) spectrometer (AIM-8800, Shimadzu), nuclear magnetic resonance (\u003csup\u003e1\u003c/sup\u003eH NMR) spectrometer (AVANCE NEO 600MHz), field-emission scanning electron microscope (Verios 460, FEI Corporation Bruker, Switzerland), thermogravimetric analyzer (TGA-Q500, USA), a nano-laser particle sizer (Malvern Instruments, UK), and a MARS60 rotational rheometer (Thermo Electron; Karlsruhe, Germany).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Synthesis of polyacrylamide microspheres\u003c/h2\u003e \u003cp\u003eA total of 171.2 g 3\u003csup\u003e#\u003c/sup\u003e white oil, 20.5 g Tween-80, 53.8 g Span-80, and 0.3 g AIBN was added to a 500 ml beaker and stirred well using a magnetic stirrer until a light-yellow transparent liquid was obtained. This liquid was transferred to a 1000 mL three-necked flask and set aside. Next, 96.7 g AM, 5.8 g AMPS, 7.6 g AA, 2.5 g ACMO, 2.1 g DMAAC-C\u003csub\u003e16\u003c/sub\u003e, and 0.2 g PEG200DA were weighed in a 500 ml beaker. After adding 140.5 ml deionized water, the mixture was stirred well with a magnetic stirrer until the monomer had dissolved. The pH of the aqueous phase was then adjusted to 6\u0026ndash;7 with the addition of a NaOH solution (30% mass concentration), and the mixture was transferred to a three-necked flask. After emulsification by N\u003csub\u003e2\u003c/sub\u003e under stirring for 30 min in the three-necked flask, 4 mL TBHP solution (1% mass concentration) was added, and the mixture was stirred for 10 min. Next, 3.7 mL Na\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e solution (1% mass concentration) was added, and reaction continued for 1.5 h under N\u003csub\u003e2\u003c/sub\u003e conditions. A certain amount of the TO-7 phase transfer agent was added to this solution, followed by stirring well to obtain a yellow translucent liquid (the PHM emulsion). An appropriate amount of the product was collected and washed with anhydrous ethanol, extracted through filtration, and placed in a 75℃ drying oven for 4 h, obtaining a solid powder of PHM.\u003c/p\u003e \u003cp\u003eConventional PCM without hydrophobic monomers were synthesized through parallel processes using MBA as the crosslinking agent. The synthesis routes of PHM and PCM microspheres are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a), (b).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Characterization and performance testing\u003c/h2\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.4.1. Fourier transform infrared spectroscopy\u003c/h2\u003e \u003cp\u003eThe washed, filtered and dried PHM and PCM sample powders were mixed with potassium bromide (1:100) and pressed. Their structures were characterized by FTIR in the scanning wavelength range 4000\u0026ndash;500 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2. Nuclear magnetic resonance hydrogen spectroscopy\u003c/h2\u003e \u003cp\u003eThe PHM were further characterized using \u003csup\u003e1\u003c/sup\u003eH NMR spectroscopy in deuterium oxide (D\u003csub\u003e2\u003c/sub\u003eO) solvent at a test frequency of 600 MHz.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.4.3. Scanning electron microscopy\u003c/h2\u003e \u003cp\u003eThe microsphere samples were dried, processed, and sprayed with gold in preparation for microstructural characterization using scanning electron microscopy (SEM).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.4.4. Thermogravimetric analysis\u003c/h2\u003e \u003cp\u003eThe thermal stabilities of the PHM and PCM were evaluated using a thermogravimetric analyzer. The temperature was increased from 25℃ to 600℃ at a ramp rate of 10℃/min under a N\u003csub\u003e2\u003c/sub\u003e flow (40 mL/min). The thermal decomposition rates of the microspheres were observed under nitrogen-ventilated conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.4.5. Particle size testing\u003c/h2\u003e \u003cp\u003eThe PHM and PCM (0.5% mass concentration) were dispersed in 3\u003csup\u003e#\u003c/sup\u003e white oil at room temperature. The dispersions were stirred for 10 min with a magnetic stirrer and then ultrasonicated for 5 min in an ultrasonic cleaner. The initial average particle sizes of the PHM and PCM were determined using a nano-laser particle sizer.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.4.6. Tests of expansion performance\u003c/h2\u003e \u003cp\u003e(1) Water absorption and expansion\u003c/p\u003e \u003cp\u003eA total of 0.2 g of each PHM and PCM microsphere sample powder was dissolved in 99.8 g deionized water, and the solutions were placed in a constant-temperature oven set to different temperatures (25℃, 40℃, 60℃, and 80℃). Samples were collected at different times and ultrasonicated to ensure the homogenous dispersion of microspheres. A small amount of the solution was inserted into the nano-laser particle sizing instrument for average particle size measurements.\u003c/p\u003e\u003cp\u003e\u003cspan\u003e2. Salt resistance testing\u003cbr\u003e\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eA total of 0.2 g each PHM and PCM microsphere sample powder was dissolved in 99.8 g brine at different mineralization levels (5000, 10000, 20000, 40000, and 80000 mg/L). Samples were collected at different times, and their average particle sizes were measured with the nano-laser particle sizer.\u003c/p\u003e\n\u003cp\u003eThe expansion multiplicities of the samples prepared at different mineralization levels and temperatures were calculated based on the change in the average particle size before and after microsphere expansion. The expansion factor \u003cem\u003eQ\u003c/em\u003e of the microspheres was calculated as\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:Q=\\frac{{D}_{2}-{D}_{1}}{{D}_{1}}\\times\\:100\\%\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e (1\u0026ndash;1)\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003eD\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eD\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e are the average particle sizes before and after expansion, respectively (both in nm).\u003c/p\u003e\n\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\n \u003ch2\u003e2.4.7. Viscoelasticity testing using rheometry\u003c/h2\u003e\n \u003cp\u003eAqueous solutions of PHM and PCM with mass concentrations of 0.2% and 0.4%, respectively, were prepared and their energy storage moduli (G\u0026prime;) and loss moduli (G\u0026prime;\u0026prime;) were determined with respect to scanning frequency and stress.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n \u003ch2\u003e2.4.8. Blocking performance testing\u003c/h2\u003e\n \u003cp\u003eA total of 1.0 g PHM microsphere sample powder was added to a 1500 mL beaker containing 999.0 g of brine at a specified mineralization level. The mixture was stirred for 20 min with a magnetic stirrer and a 1000 mL microsphere dispersion with a mass concentration of 0.1% was filtered through a 0.2 \u0026micro;m membrane in the filtration factor tester. After adding 500 mL deionized water, the pressure was tested at 0.2 MPa. The volume of filtrate was measured for 3 min and recorded as \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e. Next, a 0.2 \u0026micro;m filter membrane was placed in the filtration factor tester, 500 mL of the microsphere dispersion was added and the volume of filtrate was measured for 3 min at 0.2 MPa. The result was recorded as \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e. The blocking rate \u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e (%) was calculated as\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:{W}_{1}=\\frac{{V}_{1}-{V}_{2}}{{V}_{1}}\\times\\:100\\%\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e (1\u0026ndash;2)\u003c/p\u003e\n \u003cp\u003ewhere \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e are the filtrate volumes of the microsphere dispersion in water and brine, respectively (both in mL).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Fourier transform infrared spectroscopy\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the FTIR spectra of the PCM and PHM. The infrared spectrograms of both microspheres show the vibrational absorption peaks of the amino-group N\u0026ndash;H at 3333 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e and carboxyl-group O\u0026ndash;H of AA at 3189 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. The peaks at 2921 and 2850 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e are assigned to the C\u0026ndash;H stretching vibrations of the methylene and methyl groups, respectively. The strong absorption peaks observed at 1673 and 1449 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e are related to the vibrational absorption peaks of C\u0026thinsp;=\u0026thinsp;O and bending vibrational absorption peak of C\u0026ndash;H in methylene, respectively, and the peak at 1316 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e belongs to C\u0026ndash;N stretching vibrations in ACMO. The peaks at 1190 and 1039 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e correspond to the stretching vibrations of S\u0026thinsp;=\u0026thinsp;O and S\u0026ndash;O, respectively, in the sulfonic acid moiety in AMPS. The peak at 1112 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e is assigned to the stretching vibrations of C\u0026ndash;O\u0026ndash;C in ACMO. The peak at 768 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e in the spectrogram of PHM, which is absent in the PCM spectrogram, corresponds to the bending vibrations of \u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash; in the long-chain alkyl group in the hydrophobic monomer DMAAC-C\u003csub\u003e16\u003c/sub\u003e. The infrared spectra of both microspheres also show the absorption peaks of their monomers, confirming the successful synthesis of the target products\u0026mdash;PCM and PHM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Nuclear magnetic spectrographic analysis\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the \u003csup\u003e1\u003c/sup\u003eH NMR spectrum of PHM. The strong peak at δ\u0026thinsp;=\u0026thinsp;4.79 ppm is the D\u003csub\u003e2\u003c/sub\u003eO solvent peak. The proton peaks at δ\u0026thinsp;=\u0026thinsp;1.60 and 2.16 (labeled a and b, respectively, in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) correspond to the \u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash; and \u0026ndash;CH\u0026ndash; groups on the main chain of the polymer, respectively. The peaks at δ\u0026thinsp;=\u0026thinsp;3.21 and 3.84 (labeled c and d, respectively) correspond to the \u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash; group on the morpholine ring of ACMO. The peaks at δ\u0026thinsp;=\u0026thinsp;1.40 (e) and δ\u0026thinsp;=\u0026thinsp;3.62 (f) belong to the \u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e group in AMPS and\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash; group in ACMO, respectively. The peaks at δ\u0026thinsp;=\u0026thinsp;2.32 (g), δ\u0026thinsp;=\u0026thinsp;1.05 (h), δ\u0026thinsp;=\u0026thinsp;1.30 (i), and δ\u0026thinsp;=\u0026thinsp;0.91(j) are assigned to the \u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash; group in DMAAC-C\u003csub\u003e16\u003c/sub\u003e, \u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e group attached to N\u003csup\u003e+\u003c/sup\u003e in DMAAC-C\u003csub\u003e16\u003c/sub\u003e, \u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash; group in the long-chain alkyl group attached to N\u003csup\u003e+\u003c/sup\u003e in DMAAC-C\u003csub\u003e16\u003c/sub\u003e, and \u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e group in the long-chain alkyl group in DMAAC-C\u003csub\u003e16\u003c/sub\u003e, respectively. The protons of all five monomers, AM, AA, AMPS, ACMO, and DMAAC-C\u003csub\u003e16\u003c/sub\u003e, are correctly attributed, confirming the synthesis of the target product PHM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Scanning electron microscopy\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the SEM images of PHM (a, b) and PCM (c, d). The microscopic surface of PHM microspheres was smooth with clear edges and complete sphericity. The surface of PCM microspheres was rough, showing granular or concave structure and agglomeration. The introduction of the hydrophobic monomer DMAAC-C\u003csub\u003e16\u003c/sub\u003e enhanced the hydrophobic association between the polymer chains. During polymerization or microsphere formation, the hydrophobic groups tend to aggregate with each other through van der Waals forces or hydrophobic effects, forming dense hydrophobic microregions. This internal ordering reduces the random curling of molecular chains, resulting in a more uniform and smooth surface structure. In addition, the introduction of DMAAC-C\u003csub\u003e16\u003c/sub\u003e with strong ionization groups into the PHM microspheres increased the surface charge of the PHM microspheres, leading to the fact that the PHM microspheres could inhibit inter-microsphere agglomeration through electrostatic repulsion, resulting in an increase in the dispersion of the PHM microspheres and an increase in the independent sphere-forming ability of individual microspheres, and thus the PHM microspheres had a smoother surface and a more intact sphericity than the PCM microspheres.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Thermogravimetric analysis\u003c/h2\u003e \u003cp\u003eThe thermal stabilities of the PCM and PHM were evaluated from the thermogravimetric analysis plots over the temperature range of 25\u0026deg;C\u0026ndash;600\u0026deg;C (see Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe thermal decomposition curves of the PCM and PHM are divided into three main stages. During the first stage, the PCM and PHM lose 8.29% and 5.97% of their weight, respectively, mainly because heating volatized the water and small molecules in the polymer microspheres. The weight losses during the second stage, 22.69% and 19.82% from the PCM and PHM, respectively, are attributed to volatilization of the organic matter in the polymer microspheres, along with fracture and decomposition of the amide groups as the heating continued. Eventually, the remaining organic matter in the polymers volatilized and some of the branched chains of the polymer microspheres decompose and detach from the main chains. At 500\u0026deg;C, the remaining amounts of PCM and PHM microspheres are 11.62% and 22.15%, respectively. Introducing the hydrophobic monomer DMAAC-C\u003csub\u003e16\u003c/sub\u003e strengthens the intermolecular forces of PHM and improves the thermal stability of the molecular chains. Therefore, PHM are more thermally stable than PCM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Particle size analysis\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (a), (b) shows the initial mean particle size distributions of PHM and PCM obtained by nano-laser particle sizer, respectively.\u003c/p\u003e \u003cp\u003eThe average particle sizes of PHM and PCM are 68.69 and 146.1 nm, respectively. PHM are smaller and more homogenous and exhibit a narrower particle size distribution (37.56\u0026ndash;125.6 nm) than PCM. The higher homogeneity of PHM is attributed to the use of the hydrophobic DMAAC-C\u003csub\u003e16\u003c/sub\u003e monomer, which enhances the polymer intermolecular chains association by strengthening the bonding effect between polymer molecular chains. The more compact and stable spatial network structure formed inside microspheres reduces the particle size of PHM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e3.6. Expansion performance testing\u003c/h2\u003e \u003cdiv id=\"Sec22\" class=\"Section3\"\u003e \u003ch2\u003e3.6.1. Effect of time on swelling properties\u003c/h2\u003e \u003cp\u003eThe average particle sizes of the PCM and PHM (0.2% mass concentration) were monitored at different swelling times in deionized water. The results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe initial average particle sizes of PHM and PCM in the aqueous phase are 164.67 and 205.34 nm, respectively. After four days, the average PHM and PCM particle sizes increase 2.86 and 5.63 times, reaching 471.71 and 1156.39 nm, respectively. Compared with PCM, the expansion rate of PHM is lower in four days, indicating that PHM are more likely to maintain their original morphology and transportability during the injection process and will more easily penetrate small pore throats and orifices in the formation. This improves the efficiency of injection and reduces the energy consumption and cost of the injection process. In addition, the low expansion rate can avoid the premature expansion of PHM and plugging of the near-well zone, which can adjust the permeability of the formation more uniformly and increase the wave volume, thereby improving the recovery rate.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003e3.6.2. Effect of temperature on expansion properties\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e plots the average particle sizes of the PCM and PHM (0.2% mass concentration) in deionized water as functions of swelling time at 40℃, 60℃, and 80℃.\u003c/p\u003e \u003cp\u003eAt any given temperature, the expansions of PHM and PCM are initially fast and then slowed with the extension of time at the same temperature for four days. After four days of swelling at 40℃, the average particle sizes of PHM and PCM are 553.28 and 1202.39 nm, swelling 3.36 and 5.86 times, respectively, compared with their initial average particle sizes in the aqueous phase. At 80\u0026deg;C, the swelling multiplicities of PHM and PCM increase to 4.34 and 6.69 times, and their average particle sizes are 714.76 and 1374.71 nm, respectively. Compared with PCM, with an increase in temperature, the expansion rate of PHM at different temperatures is smaller. At all temperatures, the average particle sizes of PHM remain within the nanoscale after four days of expansion, indicating that a high temperature has a little effect on the ability of PHM to be transported through the stratum. This performance is mainly attributable to the introduction of the polymer molecular chains of ACMO, which contains a rigid heterocyclic structure that improves the rigidity of the polymer molecular chains and inhibits its thermal movement at high temperatures, thereby reducing the thermal degradation of chain segments. Moreover, N and O atoms in ACMO can form hydrogen bonds with water molecules and polymer chains to enhance intermolecular forces and improve polymer structure stability, making the polymer molecular chains not easy to break at high temperatures. The introduction of the hydrophobic monomer DMAAC-C\u003csub\u003e16\u003c/sub\u003e further improves the intermolecular forces and temperature-resistant properties of PHM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section3\"\u003e \u003ch2\u003e3.6.3. Effect of mineralization on swelling properties\u003c/h2\u003e \u003cp\u003eThe variation in the average particle sizes of PCM and PHM microsphere solutions (0.2% mass concentration) in water with different mineralization levels for four days at 25℃ is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe average particle sizes of PCM and PHM at the same salt concentration increase with time and decrease with increasing mineralization levels, indicating that the higher the mineralization, the slower the expansion of microspheres. After four days of dissolution at a mineralization level of 80,000 mg/L, the average particle sizes of PHM and PCM are 214.52 and 642.72 nm, expansion by 2.34 and 5.37 times, respectively. Strongly polar sulfonic acid groups in AMPS molecule enhance the tolerance of polymer microspheres to ions such as Ca\u003csup\u003e2+\u003c/sup\u003e and Mg\u003csup\u003e2+\u003c/sup\u003e, providing the polymers with excellent hydration ability and decreasing their susceptibility to bilayer compression by salt ions in the highly mineralized environment. Therefore, the swelling and stability of PHM are preserved in brine, and their salt resistance is improved. Compared with PCM, PHM expand more slowly under the high-salt environment. This is because with increasing mineralization, the intermolecular bonding of PHM is enhanced, making the spatial network structure of PHM more compact. Thus, compared with PCM microspheres, PHM microspheres have good swelling retardation and better salt resistance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003e3.7. Blocking performance\u003c/h2\u003e \u003cp\u003eThe variation in the blocking rates of PHM microsphere solutions (0.1% mass concentration) in aqueous solutions with different mineralization levels at different times is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe blocking performance of PHM is affected by a combination of the swelling time and mineralization level. With the prolongation of the swelling time, the average particle size and blocking rate of PHM increase continuously in four days, and the blocking rate remains basically unchanged thereafter. Meanwhile, the blocking rate of PHM decreases with increasing the mineralization degree. This is mainly because the ionic strength of the solution increases at high mineralization levels, compressing the double layer formed on the microsphere surface and affecting the swelling behavior of the polymer microspheres. The test results show that the blocking rate of PHM at different mineralization levels is greater than 80%. This is attributed to the introduction of AMPS possessing a strong polar sulfonic acid group to the polymer molecular chains, improving the hydrophilicity of the microspheres. The formation of a stable, hydrated ionic layer attenuates the charge-shielding effect of salt ions, thereby improving the salt resistances of the polymers. In addition, the presence of the hydrophobic monomer DMAAC-C\u003csub\u003e16\u003c/sub\u003e and crosslinking agent PEG200DA endows the polymer microspheres with good elasticity and stability. Elastic deformation enables the more tight packing of the microspheres within the pore spaces of the stratum during the process of blocking, improving the blocking effect of the fine pore space in the stratum.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section2\"\u003e \u003ch2\u003e3.8. Viscoelasticity evaluation\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(a) plots the energy storage moduli G\u0026prime; and loss moduli G\u0026prime;\u0026prime; of the PHM and PCM at different mass concentrations (0.2% and 0.4%) in deionized water as a function of stress. The frequency dependencies of the same solutions are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(b).\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(a), PHM display higher G\u0026prime; and G\u0026prime;\u0026prime; than PCM at the same concentration; moreover, G\u0026prime; and G\u0026prime;\u0026prime; increase with increasing PHM concentration. At a mass concentration of 0.2%, the modulus\u0026ndash;stress curves of PHM plateau in the low-stress range, and with an increase in stress, G\u0026prime; and G\u0026prime;\u0026prime; gradually decrease. The plateau disappears when G\u0026prime; \u0026lt; G\u0026prime;\u0026prime; due to the fact that the associative structure formed between the molecular chains of the polymers is destroyed under stress, phenomenon of shear dilution occurs, and viscoelasticity of the solution decreases. PHM microspheres with a mass concentration of 0.4% showed a more pronounced linear plateau with G\u0026prime; \u0026gt; G\u0026prime;\u0026prime; over the stress scan range, with the microsphere solution being more elastic than viscous.\u003c/p\u003e \u003cp\u003eAs evidenced in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(b), the G\u0026prime; and G\u0026prime;\u0026prime; moduli of PCM and PHM increase with increasing scanning frequency. The PHM solutions with mass concentrations of 0.2% and 0.4% are more elastic, and their G\u0026prime; exceeds G\u0026prime;\u0026prime;. At the same concentration, PHM yield a higher G\u0026prime; than PCM, indicating their higher elasticity .\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e shows a schematic of the shear-resistance mechanism of PHM. A conventional crosslinker MBA has a small molecular weight and undergoes dense crosslinking, mainly with rigid chain segments, such as \u0026ndash;C\u0026ndash;C\u0026ndash; and \u0026ndash;C\u0026ndash;N\u0026ndash;, which are prone to breakage under shear forces. Compared with MBA, PEG200DA molecules are connected via \u0026ndash;C\u0026ndash;O\u0026ndash; bonds present between main polymer chains. As molecular chains can rotate around the axis of oxygen atom and can be stretched or compressed, the molecular chains structure is highly flexible; accordingly, PEG200DA improves the elasticity of PHM. In addition, as a hydrophobic monomer, DMAAC-C\u003csub\u003e16\u003c/sub\u003e increases intermolecular association among PHM, and the formation of a reticular structure improves the stability of PHM. Therefore, when PHM are subjected to stratigraphic shear, the slip and fracture of chain segments cannot occur easily, exhibiting good shear resistance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec27\" class=\"Section2\"\u003e \u003ch2\u003e3.9. Blocking mechanism\u003c/h2\u003e \u003cp\u003eThe blocking mechanism of PCM and PHM is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e(a), the PCM expand rapidly and swell before reaching the depth of the formation, resulting in a poor injection effect and a deteriorated blocking effect in the deep formation.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e(b), The slowly expanding PHM can be transported to deeper depths in the formation and exhibit high injection performance. In addition, the crosslinking agent PEG200DA and hydrophobic monomer DMAAC-C\u003csub\u003e16\u003c/sub\u003e contribute elasticity and anti-shear properties to the PHM. When subjected to formation shear and extrusion during injection into the stratum, the PHM can deform sufficiently to pass through the small pores and throats in the stratum, effective blocking the pore spaces in the deep stratum.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003e(1) A temperature and salt-resistant PHM microsphere with good swelling retardation properties was synthesized by reversed-phase microemulsion polymerization using AM, AA, AMPS, ACMO, and DMAAC-C\u003csub\u003e16\u003c/sub\u003e as the polymerization monomers, PEG200DA as the cross-linking agent. TBHP and Na\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e as the initiator. FTIR and \u003csup\u003e1\u003c/sup\u003eH NMR spectroscopies confirmed the structure of PHM, reveling that the target products were successfully synthesized. Thermogravimetric analysis showed that PHM had good thermal stability.\u003c/p\u003e \u003cp\u003e(2) The average particle size of PHM was 68.69 nm. During swelling performance test in water, PHM swelled to 2.32 and 2.86 times their initial size after two and four days, respectively, at room temperature. After four days in an aqueous solution at 40\u0026deg;C and 80\u0026deg;C, the expansion multiplicities of PHM were 3.36, 4.34 times, respectively. After four days in mineralized water (80,000 mg/L) at 25\u0026deg;C, the expansion multiplicity was 2.34 times. The synthesized PHM showed good temperature and salt resistances and slow expansion properties. Moreover, the blocking rate of a PHM solution tended to be stable and greater than 85% after four days at different mineralization levels, indicating that PHM possessed strong blocking ability. Finally, viscoelasticity test confirmed the good elasticity and shear-resistance properties of PHM, conducive to improving their injection effect.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eRui Wang: Conceptualization, Methodology, Formal analysis, Writing- original draft; Lei Wang: Funding acquisition; Zhiqiang Dang: Investigation and project administration; Peng Li: Software; Xiaojuan Lai: Supervision; Simin Zhou: Validation and visualization; Yuejing Lu: Data curation; Xiaomei Jiang: Review and editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was financially supported by the Qin-Chuangyuan \u0026quot;Scientist and Engineer\u0026quot; Team Construction Project (2024QCY-KXJ-052), Key R\u0026amp;D Program of Shaanxi Province (2024GX-YBXM-393), Key scientific research project of Shaanxi Provincial Department of Education (22JT002) and the Youth Innovation Team Project of Shaanxi Universities(24JP022).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll of the material is owned by the authors and no permissions are required.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis declaration is not applicable. Our research does not need to use humans or animals as research objects.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere are no conflicts of interest to declare.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eK. Tian, G. Fei, S. Li, Y. Han, C. Wang, Q. Chen, W. Pu, M. Wang. Preparation of an amphiphilic BaTiO3 nanofluids and its application to oil displacement in low-permeability reservoirs[J]. Journal of Molecular Liquids, 2025, 426 127350-127350.\u003c/li\u003e\n\u003cli\u003eS. Jiang, R. Guo, S. Jiang, J. Cai. Diagenesis of Deep Low Permeability Reservoir in Huizhou Sag and Its Influence on Reservoirs[J]. Applied Sciences, 2024, 14 (24): 11656-11656.\u003c/li\u003e\n\u003cli\u003eZ. Nan, N. Zhang. Development Characteristics and Development Technology Analysis of Low Permeability Oilfield[J]. 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Study and Application of Ultrafine Temperature-Resistant and Salt-Tolerant Swellable Particles in Low Permeability Reservoirs [J]. Energies, 2022, 15 (18): 6619-6619.\u003c/li\u003e\n\u003cli\u003eW. Ma, Y. Li, P. Liu, Z. Liu, T. Song. Progress of Research into Preformed Particle Gels for Profile Control and Water Shutoff Techniques[J]. Gels, 2024, 10 (6): 372.\u003c/li\u003e\n\u003cli\u003eS. Lu, Q. Bo, G. Zhao, A. Shaikh, C. Dai. Recent advances in enhanced polymer gels for profile control and water shutoff: A review[J]. Frontiers in Chemistry, 2023, 11 1067094-1067094.\u003c/li\u003e\n\u003cli\u003eM. Fu, J. Zhang, G. Li, J. Hu, P. Chen, L. Chen, H. He. Study and Application of Ultrafine Temperature-Resistant and Salt-Tolerant Swellable Particles in Low Permeability Reservoirs[J]. Energies, 2022, 15 (18): 6619-6619.\u003c/li\u003e\n\u003cli\u003eY. Li, C. Dai, Y. Wu, R. Wang. A New Type of Gelled Foam Plugging Agent with Resistance to Temperature, Salt and Dilution[J]. 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Journal of Petroleum Science and Engineering, 2022, 219.\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":"colloid-and-polymer-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Colloid and Polymer Science](https://www.springer.com/journal/396) ","snPcode":"396","submissionUrl":"https://mc.manuscriptcentral.com/cps","title":"Colloid and Polymer Science","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Nanomicrospheres, Slow expansion, Temperature resistance, Salt resistance, Plugging","lastPublishedDoi":"10.21203/rs.3.rs-6885960/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6885960/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAiming to solve the problems of the large particle size, high expansion rate of polymer microspheres currently used in anatomical water-plugging technology. In this study, acrylamide (AM), acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and 4-acrylamido-morpholine (ACMO) were used as the raw materials, and the hydrophobic monomer, hexadecyl dimethyl allyl ammonium chloride (DMAAC-C\u003csub\u003e16\u003c/sub\u003e), and the cross-linking agent poly(ethylene glycol) 200 diacrylate (PEG200DA). A slow-expanding temperature- and salt-resistant polymer nanomicrospheres (PHM) were prepared by reverse-phase microemulsion polymerization. The PHM structure was characterized using infrared spectroscopy, nuclear magnetic resonance spectroscopy, and scanning electron microscopy, and their properties were analyzed nano-laser particle sizing, and rheometry and employing the filtration factor. Results showed that the average particle size of PHM was 68.69 nm. The swelling multiplicity of PHM microspheres was 4.34 times after four days of dissolution in water at 80\u0026deg;C. The swelling multiplicity after four days of dissolution in mineralized water with a mineralization level of 80,000 mg/L at 25\u0026deg;C was 2.34 times, and the blocking rate was more than 85%. The slow expansion of the synthesized PHM under the high-temperature and high-salt conditions confirmed their good expansion performance. Viscoelasticity test showed that the synthesized PHM had good elasticity and injection properties.\u003c/p\u003e","manuscriptTitle":"Preparation and Performance Evaluation of Slow-expanding Hydrophobic Polymer Nanomicrospheres","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-04 14:06:35","doi":"10.21203/rs.3.rs-6885960/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-17T01:14:59+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-16T15:13:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-13T19:30:24+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-12T17:58:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"161127954005226518339311556557914707777","date":"2025-07-06T09:12:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"211974615397316617914792402650878415800","date":"2025-07-04T21:49:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"228401597382214496251072885716032267115","date":"2025-07-03T05:14:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-02T17:04:33+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-16T12:59:32+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-16T12:57:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Colloid and Polymer Science","date":"2025-06-13T07:42:17+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"colloid-and-polymer-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Colloid and Polymer Science](https://www.springer.com/journal/396) ","snPcode":"396","submissionUrl":"https://mc.manuscriptcentral.com/cps","title":"Colloid and Polymer Science","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e1602bef-9056-4b9a-9241-328b0cc68bce","owner":[],"postedDate":"July 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-08-25T18:53:31+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-04 14:06:35","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6885960","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6885960","identity":"rs-6885960","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}