Polyacrylamide Nanocomposite Hydrogels Research Articles

Self-adhesive, self-healing, biocompatible and conductive polyacrylamide nanocomposite hydrogels for reliable strain and pressure sensors

To realize long-term and stable applications of wearable and flexible sensors for motion detection, health analysis and wisdom medication in harsh environments, self-healing, self-adhesive, electrically conductive and biocompatible polyacrylamide (PAM) nanocomposite hydrogels are fabricated as flexible strain or pressure sensors by in situ polymerization of acrylamide in the presence of polydopamine-modified carbon nanotubes (PDA@CNTs) for effectively detecting human motions, identifying materials and their shapes, and transmitting health information. The resultant PDA@CNT/PAM nanocomposite hydrogel exhibits a high self-healing efficiency of 97.3%, excellent biocompatibility, and strong adhesion with substrates based on hydrogen bonding and π–π stacking interactions. Based on the piezoresistive effect, the nanocomposite hydrogel-based strain sensor exhibits a high sense gauge factor of 3.93 at a strain of 400% and responds quickly with a fast response time of 76 ms when detecting human movement. Thanks to the contact electrification and the electrostatic induction, the nanocomposite hydrogel-based pressure sensor can respond to pressure linearly and generate voltage signals in the absence of an additional power supply. Furthermore, the self-powered smart ring made of the silicone rubber-coated PDA@CNT/PAM hydrogel enables efficient and concise information transmission via Morse code.

Shape memory behavior of polyacrylate-based amorphous nanocomposite hydrogel under uniaxial tension: Modeling and experimental

In the present work, a comprehensive constitutive equation was developed to predict the shape memory behavior of amorphous nanocomposite hydrogel systems. The effects of interfaces of nanoparticles and micro-vessels of water with polymeric matrix and their thermal and physicomechanical properties on the model prediction were considered. An amorphous polyacrylate-based hydrogel with the glass transition temperature as a switching temperature was selected. Nanocomposite hydrogels containing 0.2 and 1.2 wt% of multiwall carbon nanotubes were prepared. The accuracy of the proposed model was evaluated with experimental data for all the selected systems. The dynamic mechanical analysis results of the shape memory behavior showed the presence of nanoparticles increased the shape fixing ratio and the rate of shape recovery of polyacrylamide nanocomposite hydrogels. The model prediction of shape recovery ratio in all systems was 100%. A comparison of the model prediction with the shape memory experimental data revealed a good agreement.

Fabrication of bentonite reinforced dopamine grafted carboxymethyl xylan cross-linked with polyacrylamide hydrogels with adhesion properties

Two-dimensional bentonite nanomaterials were used as nanofiller materials to synthesize dopamine grafted carboxymethyl xylan cross-linked with polyacrylamide nanocomposite hydrogels. The properties of nanocomposite hydrogels were analyzed by FTIR, XRD, SEM, rheological analysis, swelling analysis and mechanical test. The results showed that bentonite as a nanofiller could promote the mechanical strength of nanocomposite hydrogels, in which the maximum compressive strength, maximum tensile strength and elongation at break of composite hydrogel were 42.17 kPa, 218.29 kPa and 436%, respectively. In addition, the catechol of dopamine imparted nanocomposite hydrogels with adhesion properties, and the composite hydrogels could adhere to glass, plastic, metal and PTFE.

Technology Focus: Oilfield Chemistry (September 2021)

As production chemists, we are all aware of the overall concepts of improved oil recovery (IOR) and enhanced oil recovery (EOR). Perhaps, though, fewer of us are aware of the different idiosyncrasies that exist within (and even between) these two broad categories of recovery and then how chemistry and chemicals can have an effect upon these processes. I would like to propose that the lines once were quite distinct between IOR and EOR: IOR was a standard waterflood operation, and EOR (from a chemist’s perspective) was the addition of chemistry to that waterflood (typically polymer or surfactant). Nowadays, the science has evolved massively to create many sub-genres of IOR and EOR. A waterflood is rarely just a waterflood anymore. We can alternate water and gas injection. We can add chemical conformance aids to direct better the flow of water. We can change the salinity of the water to promote better wettability for higher recovery factors. The list goes on. One just has to search out the number of EOR papers vs. (pretty much) every other discipline of production chemistry to see the commitment this industry still has to the research of this discipline. In recent years, the focus has tended to move away from deep-reservoir EOR to focus on near-wellbore stimulation. Interestingly, the mechanistic considerations that we make as production chemists are nearly identical in all cases, and significant synergies exist between these subdisciplines. Therefore, from the recent research published by SPE, two focused topics of IOR/EOR have arisen: the use of nanoparticles and the use of water-shutoff technologies. Nanoparticle use is gaining significant traction in the oil and gas industry, and field applications are now being reported. The area of IOR/EOR is no exception. Water shutoff is not a new technology area. However, are these established, production-sustaining IOR techniques seeing a resurgence caused by the headwinds our industry has faced during the COVID-19 pandemic? Recommended additional reading at OnePetro: www.onepetro.org. OTC 30123 - Thermal and Rheological Investigations on N,N’-Methylenebis Acrylamide Cross-Linked Polyacrylamide Nanocomposite Hydrogels for Water-Shutoff Applications by Mohan Raj Keishnan, Alfiasal University, et al. IPTC 20210 - Chemical and Mechanical Water Shutoff in Horizontal Passive ICD Wells: Experience and Lessons Learned in Giant Darcy Reservoir by Mohamed Abdel-Basset, Schlumberger, et al. SPE 203831 - Efficient Preparation of Nanostarch Particles and Mechanism of Enhanced Oil Recovery in Low-Permeability Oil Reservoirs by Lei Zhang, China University of Geosciences, et al.

Fabrication of novel MXene (Ti3C2)/polyacrylamide nanocomposite hydrogels with enhanced mechanical and drug release properties.

A highly stretchable nanocomposite (NC) hydrogel was fabricated via in situ free radical polymerization of acrylamide. In particular, an exfoliated two-dimensional MXene (Ti3C2) nanosheet was utilized as a crosslinker instead of traditional organic crosslinkers. The exfoliated Ti3C2 nanosheets were confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS) measurements. Compared with traditional organic crosslinked N,N-methylene bisacrylamide (BIS)/polyacrylamide (PAM) hydrogels (fracture strength of 32.0 kPa and elongation of 109.6%), the synthesized Ti3C2/PAM NC hydrogels exhibited greatly improved mechanical properties with fracture strengths of 66.5 to 102.7 kPa, compressive strengths of 400.6 to 819.4 kPa and elongations at break of 2158.6% to 3047.5% as the Ti3C2 content increases from 0.0145% to 0.0436%. The enhanced mechanical performances can be attributed to the honeycomb-like fine structure with uniform pores as well as more flexible polymer chains in NC hydrogel networks. When loaded with drugs, Ti3C2/PAM NC hydrogels exhibited good sustained-release performance, higher drug loading amounts (97.5-127.7 mg g-1) and higher percentage releases (62.1-81.4%), greatly superior to those of the BIS/PAM hydrogel (46.4 mg g-1, 45.0%). Our work reveals the application of MXene materials in the fabrication of NC hydrogels with enhanced mechanical and drug release behaviors.

Layered Rare-Earth Hydroxide/Polyacrylamide Nanocomposite Hydrogels with Highly Tunable Photoluminescence.

Polymer nanocomposite (NC) hydrogels, with 3D networks composed of delaminated inorganic nanoparticles and a polymer matrix, usually display super mechanical toughness. However, the few types of inorganic materials and relatively scarce research for NC hydrogel functions seriously limit their applications. For the first time layered rare-earth hydroxide (LRH)/polyacrylamide NC hydrogels with highly tunable photoluminescence (PL) function are reported, prepared via a convenient and green in situ polymerization process. Interestingly, the NC hydrogels reveal exciting multicolored PL phenomenon (green, yellow, orange, reddish-orange to bluish violet), long luminescence lifetime, and relatively high quantum efficiency. Furthermore, the fascinating PL function is highly tunable by adjusting LRH constituent or its concentration, and excitation wavelength. The results highlight the fabrication and applications of functional polymer NC hydrogels with highly tunable PL function.

Transparent h- BN/polyacrylamide nanocomposite hydrogels with enhanced mechanical properties

Abstract In this study, a facile way has been proposed to prepare transparent, tough and flexible polyacrylamide (PAM) hydrogels which is composed of a dually crosslinked single network by chemical crosslinking of N , N ′-methylenebisacrylamide (BIS) and physical crosslinking of hydrophilic hexagonal boron nitride ( h- BN) nanosheets. The resulting h- BN/PAM nanocomposite hydrogels are highly transparent, and exhibit significantly enhanced mechanical properties compared to the dark (GO)/PAM nanocomposite hydrogels or chemical crosslinking PAM hydrogels. Thus it opens up new opportunities for developing next-generation transparent, tough and flexible hydrogels that hold great promise in such important applications as light responsive soft robot and liquid microlenses.

Tough and highly stretchable polyacrylamide nanocomposite hydrogels with chitin nanocrystals

Chitin nanocrystals (CNCs) that were 10–20nm wide and 100–500nm long were synthetized via acidolysis and characterized with various methods. To avoid the flocculation of CNCs in the initiator solution during acrylamide polymerization, chitosan was selected as a surface modifier. The chitosan-modified CNCs were employed as multifunctional crosslinkers for the polyacrylamide (PAAm) nanocomposite (NC) hydrogels. The NC gels were tough and stretchable; for example, the maximum tensile strength and the elongation at break of the NC gels were 90kPa and 3070%, respectively. The dynamic shear modulus of the NC gels was also significantly higher than that of the PAAm. The NC gels were nearly free of residual strain after 2000% elongation. The microstructures of all NC gels were porous, with a pore size of 20–100μm. The maximum equilibrium swelling degree of the NC gels was 3800%. The improvement in the properties of the NC gels is attributed to the good dispersion of CNCs and the interfacial interactions in the composites. This work developed PAAm NC hydrogels with CNCs for application as absorbent or biomedical material due to the high mechanical properties, high absorb ability and good biocompatibility of CNCs and explored new applications for CNCs as well.

Effect of Process Variable on the Gelation Time of Sulfonated Polyacrylamide Nanocomposite Hydrogel

Among the methods available to reduce water production during oil recovery, injecting a gelling system composed of a polymer and a crosslinker has been widely used. In this study, a Plackett-Burman design was used for screening a large number of factors such as concentrations of polymer, crosslinker, pH, temperature, and presence or absence of NaCl, CaCl2, MgCl2, KCl, thiourea, sodium lactate, and nanoclay on the gelation time of sulfonated polyacrylamide nanocomposite hydrogels by rheological tests. Among these factors, temperature, pH, and CaCl2 concentration were found to have the greatest effect on the gelation time. The effects of these three factors and their interactions on the gelation time were then determined by using central composite design of response surface method. As a result, the interactions of CaCl2 concentration with temperature and pH were considerably more than the interactions of pH and temperature on the gelation time. At low pH (3 < pH < 7), the gelation time decreased by decrease of pH while at CaCl2 concentration of 3750–11250 ppm and at 7 < pH < 11, the gelation time increased with the increase of pH. It was found that temperature was the most effective parameter to control the gelation time.

Synthesis and characterization of mechanically flexible and tough cellulose nanocrystals–polyacrylamide nanocomposite hydrogels

The unique combinations of hard and soft components with core/shell structures were proposed to synthesize high strength nanocomposite hydrogels. The elastomeric hydrogels containing rod-like cellulose nanocrystals (CNCs) core and polyacrylamide shell were made from aqueous solutions via free radical polymerization in the absence of chemical cross-links. The obtained hydrogels possessed greater tensile strength and elongation ratio when compared with chemically cross-linked counterparts. Oscillatory shear experiments indicated that CNCs interacted with polymer matrix via both chemical and physical interactions and contributed to the rubbery elasticity of the hydrogels. The nanocomposite hydrogels were more viscous than the chemical hydrogels, suggesting the addition of CNC led to the increase of energy dissipating and viscoelastic properties. The network structure model was proposed and it suggested that the high extensibilities and fracture stresses were related to the well-defined network structures with low cross-linking density and lack of noncovalent interactions among polymer chains, which may promote the rearrangements of network structure at high deformations.

Effect of magnetization on the gel structure and protein electrophoresis in polyacrylamide hydrogel nanocomposites

AbstractIn this study, polyacrylamide nanocomposite hydrogels were formulated in combination with sodium montmorillonite (MMT) in the presence of a 2‐T magnetic field. This top‐down nanomanufacturing approach led to interesting changes in the internal structure of the gel and ultimately to a dramatic improvement in the ability of the composite to separate the two protein probes, ovum serum albumin and carbonic anhydrase. The morphology of the nanocomposite hydrogel was analyzed with cryogenic scanning and transmission electron microscopy, wide‐angle X‐ray diffraction, and small‐angle scattering to determine whether morphological changes would correlate with this improved separation. As the volume fractions of MMT were well under 1% in this study (because of aqueous swelling), scattering data were dominated by the polymer structure. Significant morphological changes were noted at two length scales: (1) the hydrogel cell structure, at hundreds of nanometers, appeared to exhibit changes in the anisotropic orientation with magnetization, and (2) the polyamide structure, at tens of nanometers, exhibited decreasing pore size (small‐angle X‐ray scattering). The separation data correlated most closely with a reduction in pore size; however, an additional contribution to separation from local electrostatic effects from the presence of charged MMT in the cell walls could not be discounted. The change in the pore size associated with processing may have been due to the MMT presence altering the diffusion rates of the reactants during polymer formation. The method demonstrated herein could be used ultimately to separate proteins in their native state, with the potential retention of function for downstream applications, such as novel detection techniques or purification. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Swelling behavior of sulfonated polyacrylamide nanocomposite hydrogels in electrolyte solutions: comparison of theoretical and experimental results

Nanocomposite hydrogels were prepared by cross-linking of aqueous solutions of sulfonated polyacrylamide/sodium montmorillonite with chromium triacetate as ionic cross-linker. The effect of montmorillonite content on equilibrium swelling in NaCl and CaCl2 solutions, ultimate storage modulus and effective cross-link density was evaluated. The limiting storage modulus of the nanocomposite (NC) hydrogels dropped by increasing montmorillonite content up to 1,000 ppm, and then it increased by further montmorillonite loading. A mechanism is proposed for the formation of PAMPS/Na+-MMT/Cr3+ NC hydrogels. According to this mechanism, the drop in limiting storage modulus of the NC gels at low Na+-MMT concentration is due to ionic interactions between the negative layers of sodium montmorillonite and Cr3+, leading to decreased cross-link density. However, the increase of the limiting storage modulus of the NC gels at high clay concentration results from the strong interactions between the polyacrylamide chains and clay platelets. The equilibrium swelling ratio of the NC networks decreased with increase of montmorillonite content in both aqueous NaCl and CaCl2 solutions. In addition, the experimental swelling data of these NC hydrogels were described by a modified Flory–Rehner theory. The modified model was sensitive to montmorillonite concentration and it described adequately the swelling data for NC gels in NaCl solutions. Nevertheless, theoretical predictions showed some deviations from experimental results for swelling of NC hydrogels in CaCl2 solutions.

High strength poly(acrylamide)-clay hydrogels

A series of polyacrylamide nanocomposite hydrogels were synthesized by in situ free radical polymerization of acrylamide (AAm) with ethylene glycol dimethacrylate (EGDMA) as a crosslinker in the presence of sodium montmorillonite (NaMMT) and organically modified montmorillonite (OrgMMT) clays. Modification of MMT was carried out with a quaternary salt of coco amine as intercalant having a styryl group whose contribution to both polymerization and crosslinking reactions via its reactive double bond was confirmed by solid state NMR. Exfoliation success was checked with X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques whereas mechanical performance was followed with uniaxial compression experiment. It has been found that exfoliated PAAm nanocomposites having 0.5% OrgMMT had both the maximum equilibrium swelling in water and compression strength as well as improved thermal stability due to the special and beneficial morphology observed via scanning electron microscopy (SEM).

A novel polyacrylamide nanocomposite hydrogel reinforced with natural chitosan nanofibers

Polyacrylamide (PAM) was used as a matrix material for fabricating novel nanocomposite hydrogels reinforced with natural chitosan nanofibers (CNFs) via in situ free-radical polymerization. The nanocomposite's structure, strength, morphology and rheological properties were investigated. The results showed that the CNFs had a strong interaction with PAM through hydrogen and covalent bondings. The CNFs acted as a multifunctional cross-linker and a reinforcing agent in the hydrogel system. The compression strength and storage modulus of the nanocomposite hydrogels were significantly higher than those of the pure PAM hydrogels and the corresponding PAM/chitosan semi-interpenetrating polymer network (PAM–SIPN) hydrogels. The swelling ratio (SR) of the nanocomposite hydrogels was lower than that of the PAM hydrogel, but was similar to that of the PAM–SIPN hydrogel. Among the CNF contents used, the 1.5wt% CNF loading level showed the best combined swelling and mechanical properties for the hydrogels.

Effect of montmorillonite on gelation and swelling behavior of sulfonated polyacrylamide nanocomposite hydrogels in electrolyte solutions

Nanocomposite hydrogels were prepared by cross-linking of aqueous solutions of sulfonated polyacrylamide/sodium montmorillonite with chromium triacetate. The gelation process and effects of clay content and ionic strength on swelling behavior were investigated. X-ray diffraction patterns indicated that exfoliated type of microstructure was formed. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the nanocomposite (NC) gels decreased with increasing clay content up to 1000 ppm, but it increased by further increase of Na +-montmorillonite concentration. It was also found that with increasing the clay content, the viscous energy dissipation properties of the nanocomposite gels increased. The swelling ratio of nanocomposite gels in tap water decreased as the concentration of the clay increased. However, nanocomposite gels showed higher resistance against syneresis in electrolyte solutions as compared with unfilled gels. Therefore, they are potentially good candidates for enhanced oil recovery applications.

Preparation and Swelling Behavior of Partially Hydrolyzed Polyacrylamide Nanocomposite Hydrogels in Electrolyte Solutions

In this research, nanocomposite hydrogels were prepared by cross‐linking of partially hydrolyzed polyacrylamide/sodium montmorillonite aqueous solutions with chromium triacetate. The gelation process and influence of nanoclay content and salt concentration on swelling behavior were investigated. Study of gelation behavior using dynamic rheometry method showed that increasing the nanoclay content decreases the storage modulus, due to the partial adsorption of polymer chains onto the clay surface and ionic interaction between negative layers of sodium montmorillonite and Cr.3+ By increasing the cross‐linker concentration of the gelation system, the viscous energy dissipation properties of the nanocomposite gel decreases. Swelling ratio of the nanocomposite gels in distilled water decreased as the concentration of the nanoclay increased. However, nanocomposite gels showed lower salt sensitivity in electrolyte media compared with unfilled gels.