Polymer Microgels Research Articles

Rheological behaviour of pure clay and coarse-grained clay suspensions using an inclined blade vane-in-cup

Mixtures of clay and sand suspended in water are complex systems encountered in many industrial and environmental applications, but their understanding and modelling are still limited and require further investigations. In this way, the rheological behaviour of pure non-thixotropic clay and coarse-grained clay suspensions is investigated with a rotational rheometer equipped by an inclined blade vane-in-cup, where the type and the volume fraction of both fine clay and coarse materials are varied. The Herschel–Bulkley model τ = τ y + K γ ̇ n is used to describe successfully the flow curves of suspensions relating the shear stress τ to the shear rate γ ̇ , from which the yield stress τ y , the consistency K and the index n are deduced. The main contributions of this study are (i) to validate the inclined blade vane-in-cup for the estimation of the rheological behaviour of polymer microgels, pure clay suspensions, and coarse-grained clay suspensions, (ii) to conclude on the most appropriate model type to predict the yield stress of pure clay suspensions over a wide range of fine clay volume fractions, and (iii) to highlight how frictional contacts of coarse grains may play a role on the bulk yield stress of coarse-grained clay suspensions. We believe that this work would be useful for improving the rheological description of cohesive suspensions in geophysical and industrial applications. • Rheological measurements are performed on pure clay and coarse-grained clay suspensions. • The inclined blade vane allows to estimate the rheology of complex fluids containing grains. • The most appropriate models are provided to quantify the yield stress of suspensions. • The type of coarse materials may affect the bulk yield stress due to frictional contacts.

Effect of network topology and crosslinker reactivity on microgel structure and ordering at liquid-liquid interface.

Polymer microgels synthesized in silico were studied at a liquid-liquid interface via mesoscopic computer simulations and compared to microgels with ideal (diamond-like) structure. The effect of crosslinkers reactivity ratio on the single particle morphology at the interface and monolayer behavior was examined. It was demonstrated that single particles deform into an explicit core-corona morphology when adsorbed at the interface. An increase in the crosslinker reactivity ratio decreased both the deformation ratio and the ratio between the core and corona sizes. Meanwhile, the compression of microgel monolayers revealed the existence of five distinct interparticle contact regimes, which have been observed experimentally in the literature. The crosslinker reactivity ratio appeared to define the compression range in these regimes and the sharpness of the transition between them. In particular, the higher the crosslinker reactivity ratio, the smaller the corona, and in turn, the narrower the range of the intermediate regime comprising both core-core and corona-corona contacts. The obtained results demonstrate that the more realistic model of microgels synthesized via precipitation polymerization allows for a more accurate prediction of the properties of the microgels at a liquid-liquid interface in comparison to the conventional diamond-like lattice model.

Polymer microgels for the stabilization of gold nanoparticles and their application in the catalytic reduction of nitroarenes in aqueous media.

Polymer microgels containing a polystyrene core and poly(N-isopropylmethacrylamide) shell were synthesized in aqueous media following a free radical precipitation polymerization. Au nanoparticles were fabricated into the shell region of the core–shell microgels denoted as P(STY@NIPM) by the in situ reduction of chloroauric acid with sodium borohydride. Various characterization techniques such as transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV-visible) and Fourier transform infrared spectroscopy (FTIR) were used for the characterization of Au–P(STY@NIPM). The catalytic potential of Au–P(STY@NIPM) toward the reductive reaction of 4-nitrophenol (4NP) under various reaction conditions was evaluated. The Arrhenius and Eyring parameters for the catalytic reduction of 4NP were determined to explore the process of catalysis. A variety of nitroarenes were converted successfully into their corresponding aminoarenes with good to excellent yields in the presence of the Au–P(STY@NIPM) system using NaBH4 as a reductant. The Au–P(STY@NIPM) system was found to be an efficient and recyclable catalyst with no significant loss in its catalytic efficiency.

Enhanced scavenging of a minor component from mixtures of two immiscible liquids by hollow polymer microgels

Hollow soft nanoparticles possess both the high absorption capacity and the ability to change their shape.

Preparation and Properties Study of Magnetorheological Fluids with Carbonyl Iron Powder Coated with High Polymeric Microgels

Preparation and Properties Study of Magnetorheological Fluids with Carbonyl Iron Powder Coated with High Polymeric Microgels

Synthesis and In Vitro Evaluation of Aspartic Acid Based Microgels for Sustained Drug Delivery.

The main focus of the current study was to sustain the releasing behavior of theophylline by fabricated polymeric microgels. The free radical polymerization technique was used for the development of aspartic acid-co-poly(2-acrylamido-2-methylpropanesulfonic acid) microgels while using various combinations of aspartic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N′,N′-methylene bisacrylamide as a polymer, monomer, and cross-linker, respectively. Ammonium peroxodisulfate and sodium hydrogen sulfite were used as initiators. Characterizations such as DSC, TGA, SEM, FTIR, and PXRD were performed for the fabricated microgels to assess their thermal stability with unreacted polymer and monomer, their surface morphology, the formation of a new polymeric system of microgels by evaluating the cross-linking of functional groups of the microgels’ contents, and to analyze the reduction in crystallinity of the theophylline by fabricated microgels. Various studies such as dynamic swelling, drug loading, sol–gel analysis, in vitro drug release studies, and kinetic modeling were carried out for the developed microgels. Both dynamic swelling and percent drug release were found higher at pH 7.4 as compared to pH 1.2 due to the deprotonation of functional groups of aspartic acid and AMPS. Similarly, sol–gel analysis was performed and an increase in gel fraction was observed with the increasing concentration of microgel contents, while sol fraction was decreased. Conclusively, the prepared carrier system has the potential to sustain the release of the theophylline for an extended period of time.

Dynamic Control of Photocatalytic Proton Reduction through the Mechanical Actuation of a Hydrogel Host Matrix.

This paper describes a photocatalytic hydrogen evolution system that is dynamically and reversibly responsive to the pH of the surrounding solution through the actuation of a microhydrogel (microgel) matrix that hosts the photocatalysts (CdSe/CdS nanorods). The reversible actuation occurs within 0.58 (swelling) and 1.7 s (contraction). ΔpH = 0.01 relative to the pKa of the tertiary amine on the microgel polymer (7.27) results in a reversible change in the average diameter of the microgel hosts by a factor of 2.4 and a change in the photocatalytic turnover frequency (TOF) by a factor of 5. Kinetic isotope effect and photoluminescence quenching experiments reveal that the scavenging of the photoexcited hole by sulfite ions is the rate-limiting step and leads to the observed response of the TOF to pH through the actuation of the microgel. Molecular dynamics simulations quantify a greater local concentration of sulfite hole scavengers for pH < pKa.

Preparation of Chitosan Based Polymer Microgels, Their Composites with Zinc Oxide Nanoparticles, and Physicochemical Investigation

Preparation of Chitosan Based Polymer Microgels, Their Composites with Zinc Oxide Nanoparticles, and Physicochemical Investigation

Composite Microgels for Imaging-Monitored Tracking of the Delivery of Vascular Endothelial Growth Factor to Ischemic Muscles.

Monitoring the supply of vascular endothelial growth factor (VEGF) to ischemic tissues provides information on its biodistribution and delivery to meet the requirements of therapeutic angiogenesis and tissue engineering applications. We herein report the use of microfluidically generated microgels containing VEGF-conjugated fluorescent carbon dots (CDs) (VEGF-CDs), a gelatin-phenol conjugate, and silk fibroin for imaging-monitored tracking of VEGF delivery to ischemic muscles. An in vitro release study and a bioactivity assay indicated that the VEGF-CDs were released in a sustained manner with high bioactivity. The microgels showed a high angiogenesis potential, along with a strong fluorescent signal, for the chicken chorioallantoic membrane and chick embryo. Imaging and studies of therapeutic modalities of the composite microgels indicated their effective localization in ischemic tissues and sustained VEGF release, which resulted in enhanced therapeutic angiogenesis of ischemic muscles. This work reveals the success of using VEGF-loaded composite polymer microgels for efficient and monitored VEGF delivery by intramuscular administration for ischemic disease treatment.

Exploration on Aqueous Lubrication of Polymeric Microgels between Titanium Alloy Contacts.

Since titanium alloys have been widely used as joint replacement biomaterials, their superficial lubrication has evolved to be a critical factor for normal use. For this purpose, one kind of typical microgel, poly(NIPAAm-co-AA), was synthesized by emulsifier-free emulsion polymerization and used as an aqueous lubricating additive between titanium alloy contacts. The results show that the as-synthesized microgels reduced the coefficient of friction by 46% and the wear volume by 45%, compared with pure water. Meanwhile, due to their thermosensitive property, the microgels were employed as smart additives to modulate the interfacial friction, which was attributed to the transition of the hydrated state and the elastic deformation of microgel particles. To further dissect the lubrication mechanism, it was found that the lubricating property of microgels was substantially associated with the formation of a hydrated layer surrounding microgels, microbearing effect, interfacial adsorption, and the colloidal stability. Looking beyond, as one kind of soft colloidal lubricant, the microgels may play an important role in the biomedical metal lubrication.

Near-Infrared-Light-Modulated Lubricating Coating Enabled by Photothermal Microgels.

As a micro-/nano-sized hydrogel, polymeric microgel not only has three-dimensional (3D) molecular networks but also displays the small-size effect, which has been widely used in various fields, such as drug nanocarrier, photonic crystal, functional coating, and aqueous lubrication. In this work, a photothermal lubricating coating was prepared using polymeric/inorganic hybrid microgels and its surficial friction was deliberately modulated by the remote irradiation of near-infrared (NIR) light. Specifically, a photothermal hybrid microgel, Fe3O4@poly(N-isopropylacrylamide-co-polyacrylic acid) (Fe3O4@PNA), was first fabricated and then sprayed onto poly(ethyleneimine) (PEI)-modified substrate to form a lubricating microgel coating. At room temperature, this microgel coating was hydrophilic and achieved good hydration lubrication with relatively low friction. After the introduction of NIR light, the photothermal microgel coating converted light energy into heat energy for increasing its own temperature rapidly. Due to the thermosensitive PNA shell, the wettability of the coating was transformed to hydrophobicity above the lower critical solution temperature (LCST), resulting in a remarkable increase in friction. In other words, the surficial friction of this microgel coating could be reversibly modulated using NIR light. This work expands the application scope of microgels in the field of aqueous lubrication and introduces the functional microgels into making the smart lubricating coating for the first time. This basic research in the field of friction control may provide an efficient strategy for the design of interfacial sensing, controlled transmission, and intelligent manipulator.

Micro-gel thin film molecularly imprinted polymer coating for extraction of organophosphorus pesticides from water and beverage samples

Molecularly imprinted polymers (MIPs) have become an important class of materials for selective and efficient adsorption of target analytes. Despite versatility of MIPs for fabrication in numerous formats, these materials have been primarily reported as solid phase extraction packing materials. An effective thin film MIP prepared on stainless steel substrate is reported here for high throughput enrichment of organophosphorus pesticides (OPPs) from water and beverage samples followed by liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. The key factors controlling performance as well as best practices for optimized fabrication of thin film MIPs are presented. A pseudo-phase diagram is introduced to evaluate and predict the effect of the ratio of porogen (solvent, 1-octanol) volume to relative crosslinker mass on the desired polymer features (i.e., porosity, surface area, capacity, and selectivity). At low porogen ratios, a macroporous polymer with insignificant selectivity is formed, whereas at high porogen ratios a micro-gel polymer with superior selectivity towards targets is obtained. The porosity and morphology determined with nitrogen adsorption and scanning electron microscopy were attributed to specific regions in the pseudo-phase diagram. Other factors influencing selectivity and stability of the polymer, such as type of the template and its ratios with monomer (methacrylic acid) and crosslinker (ethylene glycol dimethacrylate) were optimized. The prepared thin film MIPs were characterized using adsorption isotherms and adsorption kinetics, and evaluated for matrix effects (high humic acid content) and cross-reactivity in presence of other pesticides and pharmaceuticals. The optimized method provided limits of quantitation (LOQs) ranged from 0.002 to 0.02 ng mL−1 in water and from 0.095 to 0.48 ng g−1 in apple juice. Regarding inter-device variability (CV∼10% without normalization), excellent linearity (R2 > 0.99), satisfactory accuracies (90–110%) and precisions (<15%) were obtained.

Silver nanoparticles supported on smart polymer microgel system for highly proficient catalytic reduction of Cr+6 to Cr+3 with formic acid

AbstractPoly(styrene@N‐isopropylmethacrylamide‐methacrylic acid) [P (St‐NM)] microgels were prepared via seed facilitated emulsion polymerization process. In situ reduction of silver ions was carried out to generate Ag nanoparticles in the voids of shell region of polymer microgels. Synthesized P (St‐NM) and Ag‐P (St‐NM) particles were characterized by UV–Vis spectroscopy, transmission electron microscopy (TEM), Fourier‐transformed infrared spectroscopy (FTIR), and X‐ray diffraction (XRD). The stability of Ag nanoparticles within P (St‐NM) system over the wide range of pH and temperature is also a part of this study. Thus, prepared Ag‐P (St‐NM) was tested for its catalytic efficiency against reduction of K2Cr2O7 using formic acid (FA) as reductant. Factors affecting catalytic efficiency of Ag‐P (St‐NM) system towards transformation of Cr+6 to Cr+3 were investigated. Other toxic chemicals can also be reduced using same catalytic system.

ThermosensitivePMMAcore/oligo(ethylene glycol)‐based shell microgels as drug carriers in detoxification treatment

AbstractThe core‐shell structured polymer microgels were synthesized by coating the hydrophobic poly(methyl methacrylate) (PMMA) sphere cores with hydrophilic nonlinear poly(ethylene glycol)‐based gel shell layer. The uniqueness of these core‐shell microgels lies in the integration of the PMMA core microsphere with strong hydrophobicity and the novel oligo(ethylene glycol)‐based gel layer with well‐defined thermosensitivity for improving loading/release efficacy of two detoxification drugs (chlorpromazine and diltiazem). The hydrophilic shell is composed of hydrophilic copolymer of 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO2MA) with oligo(ethylene glycol) methyl ether methacrylates (MEO5MA). It was found that the molar ratio of two shell monomersn(MEO2MA)/n(MEO5MA) of 1:6 was an ideal matching value for production of the P(MEO2MA)/P(MEO2MA‐co‐MEO5MA) core‐shell microgels with tunable volume phase transition temperature and excellent colloidal stability across the physiologically important temperature range. Moreover, chlorpromazine‐ and diltiazem‐loaded microgels can show an obvious thermosensitive release and in vitro sustained‐release characteristic up to 80 h.

Electroresponsive microgel able to form a monolayer on gold through self-assembly

We present a novel microgel with the capacity for self-assembly, the volume of which can be altered by performing the appropriate redox reaction. The initial thermoresponsive microgel was synthesized from N-isopropylacrylamide and N-(3-aminopropyl)methacrylamide, with N,N′-bisacryloylcystine used as the crosslinker. The obtained microgel polymer network was modified with benzoquinone through the Aza-Michael addition reaction. The influence of the redox state of the benzoquinone groups in the microgel on volume phase transition temperature was examined. The disulfide bridges from the N,N′-bisacryloylcystine linker were used to attach microgel particles on an Au electrode surface, forming a monolayer. The monolayer formation and the volume phase transition within the microgel were monitored with the QCM technique. The redox state of the electroactive benzoquinone groups in the polymer network appeared to be the key factor determining whether the microgel layers exist in the shrunken or swollen state. The oxidation state can be changed electrochemically and the shrinking-swelling transformation was shown to be reversible. The obtained material was also studied with dynamic light scattering technique and electron microscopies.

Crosslinked polymer encapsulated palladium nanoparticles for catalytic reduction and Suzuki reactions in aqueous medium

Acrylamide and N-isopropylacrylamide were copolymerized in the presence of a N,N-methylenebisacrylamide crosslinker to obtain poly(N-isopropylacrylamide-co-acrylamide) [P(NA)] polymer colloidal particles. Pd nano crystals with diameter of 4–8 nm were loaded into the [P(NA)] microgels by reduction of [PdCl4]-2 within dispersion of polymer microgels. The Pd NPs-loaded hybrid microgels were analysed by TEM, STEM, EDX and XRD. The catalytic ability of the Pd-[P(NA)] system was investigated towards reductive transformation of nitroarenes into corresponding aryl amines and Suzuki coupling transformation in a green solvent, H2O. The progress of catalytic reaction was examined by thin layer chromatography (TLC). Different reactants were effectively converted into their corresponding products with great to fabulous yields (extending from 75 to 97%) under gentle reaction conditions. The Pd-[P(NA)] catalyst is stable for long time and can be utilized numerous times without any notable loss in its catalytic action.

Responsive microgels-based wearable devices for sensing multiple health signals

Flexible and wearable sensors have recently found wide applications in health monitoring and human-machine interaction. Desirable features in wearable sensors are high sensitivity and multi-targets detection capability in non-invasive manners. The sensitivity and multi-analyte detection capabilities are a function of the sensing material and sensor structures. Herein, we utilize a single-layer microgels structure integrated into a wearable capacitive sensor to realize both high sensitivity and multi-targets detections. We established a responsive sensing chain of analytes-the conformational changes of polymer chains-the morphology changes of the single-layer microgels structure-device capacitive signals. The conformational changes of microgel polymer chains due to physiological signals and metabolites in body fluids induce measurable capacitive signals generated by the sensors. This work provides mechanistic insight into a stimuli-responsive chain of analytes induced molecular conformation and thus morphology changes that induce the capacitive signal in the wearable sensors. This multipurpose sensor platform demonstrates the ability to detect bacteria such as E. coli and B. subitilis, metabolites such as uric acid in sweat, and physiological signals such as sound recognition, respiration, and pulse beat.

Antibacterial and cytotoxic activity of polymer-metal hybrid nanoparticle

Recently, there is a growing demand for the polymer-nanoparticle hybrid system due to their long-term stability against aggregation and enhanced functionality for different applications in both material science and biology. In the current study, we have prepared a novel stimuli-responsive biocompatible polymer-silver nanoparticle hybrid using polymeric microgel particles as a micro-reactor in an in-situ treatment, and these hybrid particles are characterized using UV-Vis, dynamic light scattering, and transmission electron microscope with respect to their size distribution and optical properties. Next, these hybrid particles were tested for antibacterial and cytotoxic activities against Salmonella typhimurium bacteria and HeLa cancer cells, respectively using bulk-diffusion, agar diffusion assay, and MTT assay. Both bulk and agar diffusion assays confirm the antibacterial properties of the hybrid microgel-silver nanoparticles against Salmonella typhimurium. Agar diffusion assay shows a systematic trend in the increase of the width of inhibition zone as a function of increasing particle concentration and thus relating the linear relationship between hybrid nanoparticle concentration and concentration of inhibited bacteria. Similarly, linear behavior is also observed with MTT assay, where cell viability decreases linearly with an increase in hybrid particle concentration. Thus, we believe that our polymer-nanoparticle hybrid system may have a wide range of industrial applications as an antibacterial agent and in cancer therapy applications.

Water retention in sandy substrates modified by cross‐linked polymeric microgels and their complexes with a linear cationic polymer

AbstractNew synthetic soil conditioners for anti‐erosion protection of soils in the form of microgel copolymers of N‐isopropylacrylamide and acrylic acid (PAA#) and their interpolyelectrolyte complexes (IPEC#) with different surface charges are tested for optimization of water retention and porous structure in two samples of soil substrates. Water retention curves (WRCs) are used as a fundamental thermodynamic indicator of water holding capacity in soil substrates treated by new polymeric materials. Soil‐hydrological constants, as well as specific surface parameters and pore distribution curves are calculated from the WRCs using the van Genuhten model and the Voronin method in the author's modification. PAA# and anionic IPEC# with high swelling degree at a dose of 1% (by weight) increase field water capacity, available soil water range and specific surface area by 5–6 times for quartz sand, along with reorganizing its structure towards micropore dominance. For loamy sand, the same treatment was less effective with a twofold increase in field moisture capacity, double or triple increase of specific surface area, and an almost constant range of available soil water due to the strong increase of wilting point parameter. Weakly swelling linear polyacrylic acid and cationic IPEC# did not significantly affect properties of both mineral substrates.

Redox-Active Aqueous Microgels for Energy Storage Applications.

The search for new environmental-friendly materials for energy storage is ongoing. In the presented paper, we propose polymer microgels as a new class of redox-active colloids (RACs). The microgel stable colloids are perspective low-viscosity fluids for advanced flow batteries with high volumetric energy density. In this research, we describe the procedure for the anchoring of 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) redox-active sites to the polymeric chains of water-soluble microgels based on poly(N-isopropylacrylamide)-poly(acrylic acid) interpenetrating networks. Using cyclic voltammetry and EPR spectroscopy, we show that ca. 14% of 4-amino-TEMPO groups retain electroactive properties and demonstrate the reversible redox response. It allows achieving a stable capacity of 2.5 mAh/g, enabling the low-viscous catholyte with a capacity of more than 100 mAh/L.