Inverse Microemulsion Polymerization Research Articles

Temperature-sensitive polymer grafted with nano-SiO2 improves sealing and inhibition performance of shale water-based drilling fluid

Drilling fluid loss is an important factor restricting oil and gas production. The development of pores and micro-fractures in shale formations is the main cause of drilling fluid loss. In this study, silane coupling agent modified nano-SiO2 was used as the rigid core, and N-isopropylacrylamide and 2-hydroxyethyl methacrylate were used as the flexible outer shell. The temperature-sensitive blocking agent PKSHN was synthesized by inverse microemulsion polymerization method. PKSHN was analyzed and tested through Fourier transform infrared spectroscopy, simultaneous thermal analysis, transmission electron microscopy, dynamic laser scattering and other methods. The results show that PKSHN can achieve a hydrophilic/hydrophobic transition under the response temperature, with a median particle size of 189.35 nm, which can form a hydrophobic layer on the shale surface and reduce fluid intrusion into the shale formation. This study tested the performance of three drilling fluids with different densities by adjusting the amount of weighting agent. The results showed that the high-temperature and high-pressure filter losses of the three different densities of drilling fluids were all less than 10 mL. The addition of PKSHN can effectively reduce fluid loss. The rolling recovery experiment and linear expansion experiment show that after aging for 16 h at 150 °C, the rolling recovery rate is above 90 % and the linear expansion rate is below 7 %, indicating that the addition of PKSHN can effectively control the hydration expansion of shale.

Synthesis and characterization of PNM@IAM core-shell microgels through inverse emulsion polymerization and its application for heavy metal ions capture

In this study, thermo and pH-sensitive multifunctional poly (N-isopropylacrylamide-co- N,N’-methylenebisacrylamide, Poly(NIPAAm-co-MBA) - (N-4-amino-2-methylene-4-oxobutanoic acid, IAM) named as (PNM@IAM) core-shell microgels are synthesized by inverse microemulsion polymerization technique using two monomers, N-isopropylacrylamide (NIPAAm) and N-4-amino-2-methylene-4-oxobutanoic acid (IAM). The formation of the microgels are confirmed by 1H nuclear magnetic resonance (1H NMR) and attenuated total reflection fourier transform infrared (ATR-FTIR) spectra. The light transmittance study shows that the microgels prepared at different concentrations and pHs exhibit different physical properties. The phase transition temperature is increased with the addition of IAM. Dynamic light scattering (DLS) analysis reveals that the swelling of the microgels at basic environment is due to the deprotonation of the weak acid groups in IAM. The metal ion chelating test shows that the core-shell PNM@IAM could effectively absorb metal ions in highly basic environment. The absorption and release of heavy metal ions from aqueous solution could be controlled by adjusting the pH of the reaction environment.

Preparation and performance of graphene oxide-polyacrylamide based nanoscale microsphere emulsion for profile control

A new kind of in-depth profile control and displacement graphene oxide-polyacrylamide (GO-PAM) based nanoscale microsphere emulsion for enhancing oil recovery was designed by the inverse microemulsion polymerization technology, which simultaneously plays the multifunction roles of plugging pore throat, reducing water-oil interfacial tension and oil viscosity benefiting from the synergistic effect of nanoscale microsphere and GO sheets. The emulsion shows superior suspension properties, thermal stability, hydration swelling, and the excellent emulsifying ability for crude oil. The average particle size of PAM microspheres is about 40 nm, and the size of GO sheets is about 1–10 µm. Only 0.1% dispersion of GO-PAM emulsion reduces the water-oil interfacial tension by 63%, and reduces the viscosity of thick oil by 10%. And with increasing emulsion dosage to 5%, the viscosity can be reduced by more than 50%. For low permeability simulated cores, the plugging efficiency of the GO-PAM emulsion system increases from 80% to 88% compared with PAM emulsion. The microscopic oil displacement experiment shows that our designed emulsion enhanced oil recovery by 6–7%. The GO-PAM composite microsphere emulsion is expected to be a competitive candidate for in-depth profile control and heavy crude recovery.

Stability mechanism of controlled acid-resistant hydrophobic polymer nanospheres on CO2 foam

CO2 foam was an effective way to regulate CO2 mobility and control the gas breakthrough during the process of CO2 flooding. The poor stability of foam-phase restricted the enhanced oil recovery (EOR) ability of CO2 foam flooding, especially under the harsh reservoir conditions and the challenges are yet to be solved. As such, current work hypotheses that by applying the polymer nanosphere as the additive can extend the foam rupture to increase the foam-phase stability. The acid-resistant hydrophobic polymer nanosphere P(AM-AA-ARM-C16DMAAC) was prepared by the inverse microemulsion polymerization method, which used ARM and C16DMAAC as acid-resistant monomer and hydrophobic monomer, respectively. Then, the CO2 foam reinforced by anionic surfactant AOS and P(AM-AA-ARM-C16DMAAC) was developed, and the stability was compared with conventional foam system using Warning Blender method and high temperature and high pressure electromagnetic coupling agitator. Furthermore, the foam aging rules were investigated via the multiple light scattering method and double-layer glass model to further understand the CO2 foam stability mechanism of synthesized acid-resistant hydrophobic polymer nanospheres. The results demonstrated that P(AM-AA-ARM-C16DMAAC) had good swelling performance under acid environment. With the consistency of 0.2% AOS and 0.15% P(AM-AA-ARM-C16DMAAC), the CO2 foam showed the highest foam stability. The dynamic variations in the film thickness of the foam were characterized quantitatively. The prolonged liquid drainage was attributed to the foam liquid film maintained by released water and the liquid film ‘skeleton’ formed by polymer nanospheres. In addition, the formula of acid-resistant hydrophobic polymer nanospheres P(AM-AA-ARM-C16DMAAC) is adjustable under different environmental conditions. After deformation of the foam system, the polymer nanospheres could also act as plugging agent in the formation.

Inflammatory Cell-Inspired Cascade Nanozyme Induces Intracellular Radical Storm for Enhanced Anticancer Therapy.

Manipulating intracellular levels of reactive oxygen and nitrogen species (RONS) is of great potential for cancer treatment. Inspired by the natural mechanism of a radical storm in inflammatory cells via activated and regulatable biocatalysis, the authors herein report a self-powered nanozyme that can enable RONS production in tumor cells via cascade reactions. The nanozymes are constructed via glucose oxidase (GOx)-templated inverse microemulsion polymerization from acrylamide, arginine-acrylamide, ferrocene-acrylate, and N,N'-bis(acryloyl)cystamine, followed by surface coating with hyaluronic acid. After targeted delivery into cancer cells, the nanozymes are dissociated by intracellular glutathioneto release GOx, which decomposed glucose to generate gluconic acid and H2 O2 . Under such acidified conditions, H2 O2 efficiently oxidized pendant arginine residues to produce nitric oxide , transformed into a highly toxic hydroxyl radical and superoxide anion via ferrocene-mediated Fenton reaction and Haber-Weiss cycle, and simultaneously generated peroxynitrite anion via reaction between NO and ·O2 - , thus provoking the RONS radical storm to effectively eradicate A549 tumor cells both in vitro and in vivo. This nature-inspired enzyme-chemical dynamic therapy may provide a promising modality for anti-cancer treatment.

Preparation and Properties of Temperature-Sensitive P(NIPAM-AM) Nano–Microspheres in Enhanced Oil Recovery

As a new kind of water plugging and profile control agents, the polyacrylamide nano–microspheres have been experimentally applied and achieved satisfactory preliminary results in enhanced oil recovery, especially for low-permeability reservoirs. However, the larger swollen particle size and excessive hydrophilicity limit the effect at the oil–water interface. In order to further improve their profile control and flooding effect, the temperature-sensitive poly(N-isopropylacrylamide-acrylamide) nano–microspheres are prepared by inverse microemulsion polymerization. Based on the principle of conformation transition of PNIPAM triggered by simulated high temperature in reservoirs, the particle size and hydrophilicity of the microspheres are reduced, making it easier to reach the oil–water interface, reduce the oil–water interface tension, and enhance the structural disjoining pressure, which improves the spontaneous emulsification effect and removal effect of residual oil on rocks. The swelling properties, hydrophilicity, interfacial activity, and oil displacement properties of the nano–microspheres were also analyzed. The results show that the swelling ratio of the copolymerized nano–microspheres decreases to 1.5. At simulated reservoir temperature (65 °C), the water contact angle of copolymerized gel increases from 43 to 86°, indicating that its hydrophilicity decreases and shows a clear tendency to migrate to the water–oil interface. At 65 °C, 0.1 wt % PNIPAM-based microsphere emulsion (N3) reduces the oil–water interfacial tension from 17.8 to 0.9 mN m–1. The microscopic oil displacement experiment shows that the recovery efficiency of our designed temperature-sensitive nano–microspheres emulsion is increased by 7%, which is higher than that of the PAM polymer nanosphere. The PNIPAM-based temperature-sensitive nano–microspheres that can function at the oil–water interface have a potential development prospect in low-permeability reservoirs.

Preparation and crosslinking mechanism of delayed swelling double-crosslinking nano polymer gel microsphere for anti-CO2 gas channeling

CO2 flooding is often used in low permeability reservoirs, but there is general fracture in the reservoir, resulting in the problem of gas channeling. To achieve anti-gas channeling in deep formation, acrylamide (AM), sodium p-styrenesulfonate (SSS) and dimethyl diallyl ammonium chloride (DMDAAC) were used as functional monomers, N′ N-methylene bisacrylamide (MBA) and polyethylene glycol 200 diacrylate (UCA) were used as crosslinking agents, a double-crosslinking nano polymer gel microsphere (DCNPM-A) was synthesized by inverse microemulsion polymerization. The synthetic process of gel microsphere was optimized by initial particle size and swell multiple (defined the ratio of gel microsphere volume after and before water absorption) as evaluation indexes. The gel microsphere was characterized by scanning electron microscopy (SEM) and elemental analysis (EDS). The anti-gas channeling ability was evaluated by one-dimensional fracture core. The structure of the copolymer without crosslinking agent was verified by 1H NMR. The results showed that the DCNPM-A gel microsphere was regular spherical shape under the optimal synthesis process, and EDS analysis showed that the microsphere contained all the characteristic elements of monomers. The initial particle size and swell multiple of DCNPM-A gel microsphere were 217.3 nm and 13.5 respectively. The gel microsphere possessed delayed swelling. The plugging rate of DCNPM-A gel microsphere was 95.48% in the anti-gas channeling experiment. The study in this paper can provide theoretical support for the anti-gas channeling in low-permeability fracture reservoirs.

Design, preparation and properties of new polyacrylamide based composite nano-microspheres with like “ball in ball” structure

Recently, polymer gel nano-microspheres as a new kind of depth profile control agent have achieved preliminary effects in enhancing oil recovery (EOR), especially, for some low-permeability reservoirs that are difficult to enter by conventional polymer flooding. To synergistically improve the water-oil mobility ratio on the basis of blocking pore throat and adjusting water flooding profile by microgel, a new polyacrylamide composite nano-microspheres with like "ball in ball" structure are designed and prepared via inverse microemulsion polymerization in the case of pre-introducing hyperbranched polyacrylamide (HBPAM) in the water phase. Like-spheroid (HBPAM) with high rheological properties are gradually released from microspheres to achieve the synergistic effects of plugging pore throat of reservoir and viscosity improvement of the dispersion. This article uses FTIR, SEM, TEM, TGA and laser particle size analyzer to characterize the structure, morphology, thermo-stability and particle size distribution of composite microspheres. The swelling dynamics, temperature, and salt resistance of the composite microspheres are then analyzed. More importantly, the rheological properties, dispersion stability, thickening ability, emulsifying property, and oil displacement mechanism of microspheres are systematically studied. The plugging rate and oil displacement efficiency are analyzed by simulated core experiments to evaluate the application effect of microspheres. The composite microspheres designed in this paper are expected to solve the challenge that conventional polyacrylamide used in EOR is difficult to be injected in low permeability reservoirs and synergistically enhance the profile control and EOR effect of nanospheres.

An Environmentally Friendly Inverse Microemulsion Method to Synthesize Polyacrylamide.

Polyacrylamide (PAM) was prepared by a new method of inverse microemulsion polymerization, with (NH4)2S2O8-Na2SO3 as initiator and liquid paraffin/Span80-Op10/AM-H2O-NaAc as polymerization system in this paper. The effects of initiator dosage, emulsifier dosage, monomer concentration, oil–water ratio, and temperature on molecular weight, electrical conductivity, particle size distribution, and monomer conversion were studied as well. The results indicate that that the more stable Polyacrylamide (PAM) polymer was prepared under the conditions of initiator dosage of 0.4~0.5%, emulsifier dosage of 55~60%, temperature of 40~45 °C, hydrophile–lipophile balance (HLB) value of 8.0~8.2, and NaAc concentration of 3%.

A novel hydrophobically associating water-soluble polymer used as constant rheology agent for cement slurry.

During the process of well cementing in deep water, the cement slurry experiences a wide range of temperature variation from low temperature at seabed to high temperature in downhole. The elevated temperature affects the rheology of cement slurry. The change of rheology of cement slurry could influence the safety of cementing operation. The aim of this paper is to develop a new kind of hydrophobically associating water-soluble polymer (NHAWP) as an additive to prepare a constant rheology oil well cement slurry, which can be used at temperature range from 4°C to 90°C. The acrylamide, 2-acrylamide-2-methylpropionic acid and stearyl methylacrylate were applied to synthesize the NHAWP by the inverse microemulsion polymerization. Test results indicate that the critical association temperature of NHAWP is 45°C. The critical association temperature is independent of NHAWP concentration, salt concentration and alkalinity of solution. When the temperature is below 45°C, NHAWP shows little influence on the viscosity of solution. When the temperature is above 45°C, the NHAWP forms spatial network structure by intermolecular hydrophobic association and thus increases the viscosity of solution significantly. The NHAWP also displays good thermal stability and excellent salt and alkali resistance properties. In addition, the NHAWP shows nearly no negative influence on the basic properties of cement slurry, which indicates that the NHAWP can be used as a constant rheology agent to prepare a cement slurry with constant rheology in the temperature range of 4°C to 90°C.

Synthesis of water-soluble ionic terpolymers by inverse microemulsion and solution polymerization methods.

The synthesis of terpolymers can lead to very interesting combinations of monomers, which can affect the solubility of the polymer, its thermal stability or resistance in saline aqueous media. Free-radical inverse microemulsion and solution polymerization techniques were used to prepare water-soluble acrylamide-N-vinylpyrrolidone-(vinylbenzyl)trimethylammonium chloride terpolymers. The formulation of the polymerizable microemulsion was optimized by using the screening of surfactant percentage and HLB concept. The influence of synthesis temperature on the terpolymer composition and molecular weight was investigated. The reactions were carried out at 60, 70, and 75 °C for the microemulsion technique and at 40, 50, and 55 °C for the solution polymerization technique. The reaction products from both processes were water-soluble polymers, and the two techniques reached high conversions and molecular masses. Maximal molecular weights were displayed by terpolymers prepared by the solution method at 40 °C (959, 840 g mol−1) and the inverse microemulsion method at 60 °C (795, 994 g mol−1). According to NMR analysis, the highest amount of (vinylbenzyl) trimethylammonium chloride was incorporated into the terpolymer structure by the inverse microemulsion method. In contrast, the solution method yielded higher contents of acrylamide and N-vinylpyrrolidone. The viscosity properties of the terpolymers in aqueous solutions were directly correlated to their molecular weight and synthesis conditions.

Epitope‐Imprinted Nanoparticles as Transforming Growth Factor‐β3 Sequestering Ligands to Modulate Stem Cell Fate

AbstractGrowth factors (GFs) are biomolecules with potent biological effects but inherent limitations hinder their potential as therapeutic agents and cell culture supplements in tissue engineering and regenerative medicine (TERM). Biomaterials that sequester endogenous GFs by affinity binding might circumvent such limitations and thus are being increasingly investigated. Here, molecularly imprinted nanoparticles (MINPs) are proposed as specific abiotic ligands for GFs. As a proof of concept, a conformational epitope of transforming growth factor‐β3 (TGF‐β3) is designed and surface imprinted onto polyacrylamide‐based nanoparticles by inverse microemulsion polymerization. It is found that, depending on the polymerization mixture composition, MINPs can recognize and preferentially bind TGF‐β3, either in noncompetitive assays or from a complex human fluid (platelet lysate). Substrates functionalized with MINPs are then used for 2D culture of adipose‐derived stem cells. Remarkably, gene and protein expression profiles show a marked upregulation of SOX‐9, suggesting activation of TGF‐β3 signaling pathways without requiring supplementation with exogenous GF. Likewise, culturing these cells in pellets incorporating MINPs previously incubated with platelet lysate results in higher collagen II‐rich matrix deposition, compared to pellets incorporating non‐imprinted nanoparticles. In summary, results suggest MINPs can be used as cost‐effective, stable, and scalable alternative abiotic GF ligands to guide cell fate in TERM applications.

Fast DNA Extraction with Polyacrylamide Microspheres for Polymerase Chain Reaction Detection.

The fast and cost-effective DNA extraction is critical for all DNA-based detections. Here, we fabricated a new kind of polyacrylamide microsphere (PAMMP) in various sizes with two methods, spot polymerization (large size but low yield) and modified inverse microemulsion polymerization (small size but high yield). The fabricated PAMMPs have strong autofluorescence (fPAMMPs), including both visible fluorescence (VF) and near-infrared fluorescence (NIRF), which can remain very stable in various stringent conditions including strong acid and alkali and high temperature. The fabricated fPAMMPs were also highly positively charged, which could be used to effectively capture various biomolecules such as IRDye 800-labeled streptavidin and DNA. We thus developed a new method for rapid extraction (3–5 min) of DNA from various samples including bacteria, mammalian cells, plant and animal solid tissues, and human blood plasma using fPAMMPs. Moreover, the DNA captured on fPAMMPs (fPAMMP@DNA) could be effectively detected by both normal and quantitative PCR amplifications. Finally, we showed that NaBH4 treatment removed autofluorescence in fPAMMPs (PAMMPs), which could also be applied to DNA extraction and PCR detection. In conclusion, we here fabricated new kinds of fPAMMPs and PAMMPs, developed a new rapid DNA extraction method, and demonstrated their useful applications in PCR detection.

Investigation on the preparation of nanoparticles by inverse micro-emulsion polymerization for enhanced oil recovery

Polyacrylamide nanoparticles attracted increasing interest as profile control agents in oilfield development owing to the characteristics of deformation and continuous expansion in core pore. In this article, the structure and morphology of polyacrylamide nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). And the fluorescence microscopy and core displacement equipment were used to evaluate the properties of the expansion and plugging properties. Results showed that the nanoparticles prepared by inverse emulsion polymerization can be able to pass through the pores in the rocks due to the uniform particle size which is less than 500 nm. When the nanoparticles were in contact with water for 72 hours, the average particle size increased to 12.2 μm. The water-swelled nanoparticles can effectively block the high-permeability layer and improve the oil recovery in the low-permeability layer. The results obtained in this paper reveal the mechanism of elastic deformation and expansion characteristics of polyacrylamide nanoparticles, and further prove the great potential of nanoparticles to enhance oil recovery in the development of low permeability oilfields.

Surfactant-assisted graphene oxide/methylaniline nanocomposites for lead ionic sensor development for the environmental remediation in real sample matrices

Graphene oxide/methylaniline (GO/MA) nanocomposites (NCs) were synthesized by an in situ inverse microemulsion polymerization method. The characterization of nanocomposites is done by scanning electron microscope (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) methods. In addition, an efficient chemical sensor probe was fabricated with flat glassy carbon electrode (GCE) by coating with thin layer of synthesized GO/MA NCs. Then the sensor was applied for the selective detection of lead (Pb+2) ion in an aqueous phase. The sensor performance such as sensitivity (20.56 µA mM−1 cm−2) was calculated from the slope of the calibration curve. The linear dynamic range (LDR: 0.1 nM–0.01 M) was calculated on the maximum linearity line from the calibration plot. The detection limit (DL: 50.0 ± 2.5 pM) was also calculated from the slope of the calibration plot by considering of 3 N/S (signal-to-noise ratio of 3). This novel electrochemical approach introduced a reliable and efficient route to detect the heavy metal ions as selective sensor for the safety of medical, biochemical and environmental fields in broad scales.

Development and evaluation of novel nanophotosensitizers as photoantimicrobial agents against Staphylococcus aureus

The main aim of the present study was to synthetize polyacrylamide nanoparticles and to use them as photosensitizer carriers. The new monobrominated derivatives (monobrominated neutral red and monobrominated azure B) were the photosensitizers used for antimicrobial photodynamic therapy. They were loaded into the nanocarriers and their antibacterial and oxidative activities were evaluated. The polyacrylamide nanoparticles were evaluated and prepared by inverse microemulsion polymerization. The nanoparticles obtained were characterized by size, polydispersity index, and zeta potential analysis. The Dynamic Light Scattering indicated that the diameter of the particle (z-average) was optimal, with an acceptable polydispersity index. The antibacterial activity of the polyacrylamide nanoparticles loaded with photosensitizers was evaluated against Staphylococcus aureus. Both photosensitizers loaded into the nanoparticles showed great potential as antibacterial agents since they suppressed the bacterial growth. The maximum percentage of growth reduction was 35.5% (>2 Log CFU/mL), with the monobrominated azure B loaded into the nanocarrier with 2 hydroxyethyl methacrylate against methicillin resistant S. aureus. The improved physicochemical and photophysical properties of these photosensitizers were accompanied by a significant increase in the photoantimicrobial action, in conventional-sensitive and-methicillin resistant S. aureus.The results obtained clearly suggest that polyacrylamide nanoparticles loaded with photosensitizers have great potential for further application in antimicrobial photodynamic therapy.

Zwitterionic Nanohydrogel Grafted PVDF Membranes with Comprehensive Antifouling Property and Superior Cycle Stability for Oil‐in‐Water Emulsion Separation

AbstractFouling caused by oil and other pollutants is one of the most serious challenges for membranes used for oil/water separation. Aiming at improving the comprehensive antifouling property of membranes and thus achieving long‐term cyclic stability, it is reported in this work the design of a kind of zwitterionic nanosized hydrogels grafted poly(vinylidene fluoride) (PVDF) microfiltration membrane (ZNG‐g‐PVDF) with superior fouling‐tolerant property for oil‐in‐water emulsion separation. Sulfobetaine zwitterionic nanohydrogels with the diameter of ≈50 nm are synthesized by an inverse microemulsion polymerization process. They are then grafted onto the surface of PVDF microfiltration membrane, endowing the membrane a superhydrophilic and nearly zero oil adhesion property. This ZNG‐g‐PVDF membrane exhibits great tolerance and resistance to salts pH, especially an excellent antifouling property to oil‐in‐water emulsions containing various pollutants such as surfactants, proteins, and natural organic materials (e.g., humic acid). The comprehensive antifouling property of the membrane gives rise to the cyclic stability of the membrane greatly improved. A nearly 100% recovery ratio of permeating flux is achieved during several cycles of oil‐in‐water emulsion filtration. The ZNG‐g‐PVDF membrane shows great potential in treating practical oily wastewater containing complicated components in the effluent.

Understanding the semicontinuous‐heterophase, surfactant‐supported, acrylamide inverse polymerization

In this work, a simple comprehensive mathematical model, to understand the main mechanisms occurring in the semicontinuous heterophase inverse polymerization of acrylamide, is reported. A Mayo‐Lewis extended model, including nucleation and coagulation, is assessed with experimental conversion, particle density and inferred average number of radicals versus time‐data at 60°C, at three monomer addition rates. It was found that: (1) the average number of radicals is much smaller than 0.5 contrary to most of inverse emulsion and microemulsion polymerization reports, this number increased steadily along the experiments, (2) coagulation does exist in this process, and (3) the exit rate coefficient was found to present a high value, agreeing with other authors that claim a large exit rate. Conversion, the bell‐shaped number of particles' evolution and number average radicals' concentration, versus time data, are well described by the proposed model. POLYM. ENG. SCI., 58:2219–2226, 2018. © 2018 Society of Plastics Engineers

New insights into the viscosity features of cationic polyacrylamide microgels in aqueous solutions

ABSTRACTIncreasing attention has recently been paid to the rheological behavior of microgel colloids and to the physical forces that control their behavior. Here, based on a series of cationic microgels that were synthesized by inverse microemulsion polymerization, the physical forces were explored by viscosity analysis of swollen microgels with different crosslinking densities and cationic contents. The results indicate that within a wide concentration range, the viscosity curves for these cationic microgels perfectly correspond to the Krieger–Dougherty model as modified by Tan et al. In particular, the specific volume in this model decreases at the critical overlapping concentration and reveals the interaction intensity between neighboring microgels. Furthermore, the viscosity index in the Herschel–Bulkley equation indicates that the interaction domain among microgels undergoes a transfer from an electroviscous effect to osmotic deswelling with increasing concentrations. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46297.

Water-dispersible nanohydrogels of cross-linked polyacrylamide

Stable water-dispersible nanohydrogels of cross-linked polyacrylamide (PAAm) were obtained by batch (BP) and semicontinuous (SP) processes through inverse microemulsion polymerization using N,N'-methylenebisacrylamide (NMBAM) as cross-linking agent and bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) as surfactant. The effects of initiator type as 2,2'-Azobis(2-amidinopropane) hydrochloride (V-50), potassium persulfate (KPS), ammonium persulfate (APS), and benzoyl peroxide (BPO) on kinetics, particle size, and morphology were studied. It was observed that under the studied conditions, it is possible to form the inverse microemulsions using lower surfactant concentrations than those typically reported for microemulsion polymerization of this monomer. Z-average particle size (Dpz) of final latexes were in the range of 51 to 79 nm for BP, those corresponding to SP were in the interval of 118 to 225 nm, while Dpz of water-dispersed nanohydrogels varied from 530 to 825 nm conserving their spherical morphology. Particle size distributions of both latexes and the water-dispersed nanohydrogels were monomodal. High monomer conversions and fast polymerization rates were observed in all cases, achieving monomer-starved conditions when using low monomer addition rate in SP process.