Copolymer Gels Research Articles

Preparation of hydrophobic and oleophobic fine sodium bicarbonate by gel-sol-gel method and enhanced fire extinguishing performance

Functionalized sodium bicarbonate (FSB) powder with hydrophobicity and oleophobicity may provide a new solution to the increasingly severe aircraft engine fires. A one-step way to prepare hydrophobic and oleophobic powders by gel-sol-gel method was developed. Perfluoro copolymer gels were synthesized with PFEA (2-(perfluorooctyl) ethyl acrylate), MMA (methyl methacrylate) and HEMA (N-(2-Hydroxyethyl) acrylamide). The sol-forming properties of five different ratios of PFEA and MMA were investigated. As the proportion of PFEA increased, the oleophobic performance increased but the solubility of the copolymer gel in acetone decreased. The water and oil contact angles would reach the maximum values when PFEA content was the highest. When the mass ratio of PFEA to MMA exceeded 50%, functionalized sodium bicarbonate powder showed a good floating performance on water and aviation kerosene surface. In fire experiments, pure sodium bicarbonate powder was hard to extinguish aviation kerosene pool fires while FSB powder could extinguish the flame easily. The formed FSB powder layer effectively inhibited the flame from spreading on the oil surface.

Adsorptive removal of alcohols from aqueous solutions by N-tertiary-butylacrylamide (NtBA) and acrylic acid co-polymer gel

A co-polymer gel of N-tert-butylacrylamide and acrylic acid was swelled in alcohols differing in its dipole moment and H-bonding interaction parameter so as to inspect the relative affinities of the gel towards alcohols. The gel swelled 900% in ethanol, 1200% in propanol and 750% in butanol. The extent of swelling can be used as a guide for preferential removal of particular alcohol from its mixture. Studies on adsorption isotherm using different isotherm equations helped in deciding the mechanism of adsorption of ethyl alcohol. The swelling and de-swelling kinetics of the gel in ethanol, propanol, and butanol (at low concentration of 5 g/l each) followed mostly Fickian type diffusions for the processes of absorption and desorption. The scope of repeated use of the gel for the alcohol recovery was investigated and every time approximately 98% alcohol could was found to be recovered. The honeycomb morphology of the gel was accountable for such swelling of the gel.

Mechanical Properties and Failure Behavior of Physically Assembled Triblock Copolymer Gels with Varying Midblock Length

ABSTRACTMechanical properties including the failure behavior of physically assembled gels or physical gels are governed by their network structure. To investigate such behavior, we consider a physical gel system consisting of poly(styrene)‐poly(isoprene)‐poly(styrene)[PS‐PI‐PS] in mineral oil. In these gels, the endblock (PS) molecular weights are not significantly different, whereas, the midblock (PI) molecular weight has been varied such that we can access gels with and without midblock entanglement. Small angle X‐ray scattering data reveals that the gels are composed of collapsed PS aggregates connected by PI chains. The gelation temperature has been found to be a function of the endblock concentration. Tensile tests display stretch‐rate dependent modulus at high strain for the gels with midblock entanglement. Creep failure behavior has also been found to be influenced by the entanglement. Fracture experiments with predefined cracks show that the energy release rate scales linearly with the crack‐tip velocity for all gels considered here. In addition, increase of midblock chain length resulted in higher viscous dissipation leading to a higher energy release rate. The results provide an insight into how midblock entanglement can possibly affect the mechanical properties of physically assembled triblock copolymer gels in a midblock selective solvent. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2019,57, 1014–1026

Reversible Adsorption-Desorption of Zn (II) and Pb (II) in Aqueous Solution by Thermosensitive-Sulfobetaine Gel

Copolymer gel contains zwitterionic betaine N,N-dimethyl(acrylamidopropyl) ammonium propane sulfonate (DMAAPS) and thermosensitive N-isopropylacrylamide (NIPAM). Later, they were employed as reversible Zn (II) and Pb (II) adsorption-desorption in aqueous solution. The effects of temperature, monomer, cross-linker concentration, and type of ions on the swelling degree, and the adsorption amount of Zn (II) and Pb (II) ions onto the gel were investigated. In addition, the adsorption-desorption reversibility of ions was also examined. The adsorption ability and swelling degree of the gel were significantly influenced by temperature, monomer, and cross-linker concentrations. The amount of ions adsorbed onto the gel was inversely proportional to its temperature at various monomer concentrations. The swelling degree of the gel with NIPAM to DMAAPS molar ratio of 9:1 and 8:2 decreased with the increase of the temperature. However, for the gel prepared with NIPAM to DMAAPS molar ratio of 7:3, the swelling degree increased significantly as the temperature increased. It was obtained that the swelling degree of the gel in Zn(NO3)2 solution was higher than the swelling degree of the gel in Pb(NO3)2 solution. In contrast, the amount of ions adsorbed onto the gel in Zn(NO3)2 solution was slightly lower than in Pb(NO3)2 solution. Copolymer gel prepared with NIPAM to DMAAPS molar ratio of 8:2 exhibited the highest adsorption ability and swelling degree in Zn(NO3)2 and Pb(NO3)2 solutions. In addition, the copolymer gel of NIPAM-co-DMAAPS showed the reversible adsorption-desorption ability toward ions up to three cycles.

Silver nanocomposite hydrogel of Gum Ghatti with potential antibacterial property

A nanocomposite hydrogel based on the polysaccharide Gum ghatti (Gg) has been made by microwave assisted polymerization of N,N-dimethylacrylamide (DMA) in the presence of Gg. Silver nanoparticles have been incorporated into the gel by chemical reduction method. The conditions for obtaining the graft copolymer gel and its nanocomposite have been optimized. The chemical, thermal and morphological characterization of the synthesized materials have been made using FTIR, TGA, SEM, EDS, XRD and TEM techniques. Swelling studies in aqueous media indicated the influence of nanoparticles in enhancing the swelling ability of the gel by three fold. In addition, the presence Ag nanoparticles is found to impart significant antibacterial property to the gel against Gram negative and Gram positive bacteria, the effect being pronounced on the former.

SAXS and SANS Studies on the Phase‐Separated Network Structure of Amphiphilic Copolymer Composed of Poly(dimethyl siloxane) and Poly(N,N‐dimethyl acrylamide) Gels Swollen in Water and a Water/Methanol Mixture

The phase‐separated network structure of amphiphilic copolymer gels composed of poly(dimethyl siloxane) (PDMS) and poly(N,N‐dimethyl acrylamide) (PDMAA) in water and a water/methanol mixture is investigated by small angle X‐ray (SAXS) and small angle neutron scatterings (SANS). The copolymerized gel of PDMS‐co‐PDMAA exhibits bicontinuous phase‐separated domains (hydrophilic and hydrophobic) with a periodicity at the nanometer scale, and the PDMS hydrophobic domain forms a cylinder‐like core. The hydrophilic region is confirmed to be selectively swollen by water and methanol. Deuterated water and deuterated methanol are used for the SAXS and SANS measurements. The electron density and scattering length density (SLD) of the hydrophilic region vary according to the mixture ratio and adsorption amount of the solvents. The SAXS profiles (curve and scattering intensity) significantly change with the ratio D2O/methanol‐d4. On the other hand, the SANS profiles do not change significantly. The deuterated solvents cannot be distributed into the PDMS domain (core). The solvents and PDMAA hydrophilic form matrix. In these situations, as for SANS, the SLD difference between the PDMS and matrix remains almost constant. As for SAXS, in contrast to SANS, the electron density difference between the PDMS and hydrophilic domain varies with the ratio of water to methanol. The SAXS and SANS profiles can be simulated using a core‐shell cylindrical model. We found that an interfacial thin region exists between the hydrophobic PDMS and hydrophilic PDMAA/solvents. This interfacial region is determined to be composed of a solvent–poor PDMAA.

Safety and biocompatibility of injectable vaccine adjuvants composed of thermogelling block copolymer gels

Injectable thermogelling polymers have been recently investigated as novel adjuvants and delivery systems for next generation vaccines. As research into natural and synthetic biocompatible polymers progresses, the safety and biocompatibility of these compounds is of paramount importance. We have developed cationic pentablock copolymer (PBC) vaccine adjuvants based on Pluronic F127, a thermogelling triblock copolymer that has been approved by the FDA for multiple applications, and methacrylated poly(diethyl amino)ethyl methacrylate outer blocks. These novel materials have been demonstrated to effectively create an antigen depot, minimally impact antigen stability, and enhance the immune response to antigens (i.e., adjuvanticity) in mice. In this work, we investigated the safety and biocompatibility of the parent triblock Pluronic gels and the cationic PBC gels in mice. Histological analysis showed no injection site reactions and no damage to the liver or kidneys was observed upon administering the block copolymer formulations. However, the subcutaneous injection of a thermogelling Pluronic solution induced increased levels of lipids in the blood, with no further deleterious effects observed from the addition of the cationic outer blocks. This hyperlipidemia resolved within 30 days after the administration of the Pluronic formulation. To mitigate this adverse effect, the vaccine adjuvant formulations were modified by adding poly(vinyl alcohol), which allowed gelation, while reducing the amount of Pluronic in the formulation. This modified formulation abrogated the observed hyperlipidemia and no adverse effects were observed in the serum through biomarker analysis or at the injection site (i.e., inflammation) in comparison to the responses induced by administration of saline or incomplete Freund's adjuvant. These studies provide a foundation to developing these gels as adjuvants for next generation vaccines. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1754-1762, 2019.

Effect of Polymer Volume Fraction on Fracture Initiation in Soft Gels at Small Length Scales.

The influence of polymer volume fraction, ϕv on fracture initiation via puncture is studied in self-assembled triblock copolymer gels. Spherically tipped indenters of radii varying over a wide range were used to characterize puncture at length scales on the same order of magnitude as the elasto-capillary length (∼μm) and significantly below the elasto-fracture length (∼mm) for ϕv = 0.12-0.53. Critical energy release rate, Gc for ϕv = 0.12-0.30 was found to be in agreement with the predicted scaling from the classical Lake-Thomas model modified for gel fracture via the failure mechanism of chain pull-out and plastic yielding of micelles (Gc ∼ ϕv2.2). Interestingly, we demonstrate that fracture initiation energy, o, from puncture scales as o ∼ ϕv, thus, indicating the role played by different fundamental mechanisms governing fracture initiation in soft gels. Additionally, gels with ϕv = 0.53 show deviation from experimental scalings for Gc and o, likely due to a change in micellar morphology leading to anomalous fracture behavior.

Silver nanoparticle-embedded pectin-based hydrogel for adsorptive removal of dyes and metal ions

Silver nanoparticles made by green synthesis have been incorporated into pectin-based copolymer gel to make a nanocomposite gel to be used as an adsorbent material for the removal of divalent metal ions and dyes from aqueous solutions. Silver nanoparticles were obtained by mixing silver nitrate with aqueous solution of pectin followed by microwave irradiation. The nanocomposite hydrogel was obtained by the microwave-assisted polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and acrylamide (AAm) in the presence of N,N’-methylene-bis-acrylamide (MBA) in pectin solution containing silver particles. Characterization of the nanocomposite gel was done by FTIR, TGA, XRD, FESEM and EDS techniques. The system was evaluated for its capacity to adsorb cationic dye, crystal violet (CV) and metal ions [Cu(II) and Pb(II)] from aqueous solutions. The presence of Ag nanoparticles is observed to enhance the adsorption capacity of the gel for the above mentioned adsorbates. The kinetic studies revealed second-order adsorption processes which fit well into Langmuir model. The evaluation of thermodynamic parameters indicated the adsorption process to be exothermic and spontaneous. A maximum of 1950 mg/g CV, 111 mg/g Cu(II) and 130 mg/g Pb(II) could be removed from the aqueous solution which is quite high in comparison with other reported materials. The desorption studies indicated the possible reusability of the nanocomposite.

ABA-type triblock copolymer micellar system with lower critical solution temperature-type sol-gel transition

A temperature sensitive sol-gel transition induced by the self-assembly of amphiphilic copolymers and its application in industry have been the objects of increasing study. We demonstrate here a two-step, reversible addition-fragmentation chain transfer (RAFT) polymerization of an ABA-type copolymer consisting of poly(N,N-dimethylacrylamide)-b-poly(diacetone acrylamide)-b-poly(N,N-dimethylacrylamide) (PDMAA-b-PDAAM-b-PDMAA). This copolymer can be easily dispersed in water, and this dispersion is critical for its lower critical solution temperature (LCST)-type sol-gel transition, which was monitored using dynamic light scattering (DLS), transmission electron microscopy (TEM), and rheology analysis, in addition to temperature-dependent 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy (FTIR). Results revealed an abnormal sphere-to-worm micellar transition of this ABA copolymer at the LCST point, which could be affected by the length of the PDAAM block (B-block), the length as well as the distribution of the PDMAA block (A-block), and the concentration of the copolymer dispersion. Thus, copolymer dispersion could be feasibly used for drug loading at a low temperature, which could then be transformed into a gel at an elevated temperature. The loading and controllable release of the model drug of paracetamol into and out of a copolymer gel was further determined. The sustained release behavior was also studied using the Rigter-Peppas model.

Hertzian elasticity and triggered swelling kinetics of poly(amino ester)-based gel beads with controlled hydrophilicity and functionality: A mild and convenient synthesis via dropwise freezing into cryogenic liquid

Poly(amino ester)-based homo- and co-polymeric gel beads were prepared via “dropwise freezing into cryogenic liquid” method and multi-responsive properties of the prepared spherical beads were confirmed by the pulsatile swelling kinetics and the stress-strain relationships based on Hertzian elasticity. Dual pH- and ionic strength-responsive homopolymeric PDMAEMA as well as copolymeric poly(hydroxyethyl methacrylate-co-dimethylaminoethyl methacrylate) P(HEMA-co-DMAEMA) gel beads crosslinked with diethyleneglycol dimethacrylate (DEGDMA) were prepared by aqueous phase crosslinking copolymerization at subzero temperature within the millimeter-sized frozen droplets in the paraffin oil as continuous phase. With this method, spherical ionic gel beads of sizes 2–5 mm could be synthesized without using a stabilizer. The successful synthesis of PDMAEMA and P(HEMA-co-DMAEMA) gel beads was confirmed by ATR-FTIR and SEM. Modulus of elasticity of cross-linked poly(amino ester)-based gel beads in swollen state was measured as a function of the bead diameter. The relationship between the compressive elastic force and corresponding deformation was obtained to compare the experimental results with theoretical-analytical formulations using the constitutive relations from Hertzian elasticity. The effective crosslink density of gel beads produced in the same synthesis batch increased as a function of increasing bead diameter, which was attributed to the formation conditions of the beads via frozen droplets of the pre-gel solution. The synthesis pathway used for the production of gel beads from methacrylate-based monomer with a polar tertiary amino group offered one-way control over material geometry to design soft and smart materials with controlled size and porosity.

Influence of Morphology and Rheological Properties on the Mechanical and Dielectric Behavior of Block Copolymer Gels

Dielectric elastomers are materials of increasing interest in applications as electroactive polymers. In this field, materials with high dielectric constant and low elastic modulus are essential for high actuation performance, and block copolymer gels are among the best candidates for these applications. In this study SEBS block copolymer gels containing mineral oil were obtained in order to evaluate their morphological structure and rheological properties, as well as the impact of these properties on their mechanical and dielectric behavior. The variation of the dielectric constant was verified as a function of the viscosity of the SEBS gel and its morphological structure.

Temperature-responsive culture surfaces for insect cell sheets to fabricate a bioactuator

ABSTRACTFor the first time, we have fabricated insect-derived cell sheets by using temperature-responsive culture surfaces having a phase-transition temperature below 25°C. We prepared the temperature-responsive cell culture surfaces (tissue culture polystyrene, TCPS) by grafting a copolymeric gel consisting of hydrophobic N-tert-butylacrylamide (tBAAm) and N-isopropylacrylamide (IPAAm) units. First, to characterize the hydrophilic and hydrophobic properties of the copolymeric gel-grafted surfaces, static water contact angles of each surface were measured at various temperatures. By increasing the amount of tBAAm in the grafted copolymeric gel, the transition temperature of the gel was shifted to lower temperatures. At 25°C, the grafted copolymeric gel was dehydrated, and the insect-derived cells (AeAl2 cells) adhered on all the copolymeric gel-grafted surfaces. At 20°C, AeAl2 cells cannot adhere on the P(IPAAm-1.62tBAAm)-TCPS surface (the initial molar ratio of IPAAm and tBAAm (tBAAm = 1.62 mol%)) better than on other surfaces (TCPS and tBAAm = 4.88, 8.17 mol%). These two findings implied that the lower critical solution temperature of the copolymeric gel-grafted-TCPS existed from 20°C to 25°C. The laminin-coated P(IPAAm-1.62tBAAm)-TCPS surface showed temperature-dependent cell attachment and detachment properties, while AeAl2 cells were not detached from the extracellular matrix uncoated P(IPAAm-1.62tBAAm)-TCPS surface. AeAl2 cells and insect muscle cells were harvested as the respective sheets.

Influence of poly(ε-caprolactone) end-groups on the temperature-induced macroscopic gelation of Pluronic in aqueous media

Temperature-induced gelation of amphiphilic copolymers in aqueous media has attracted a great deal of interest in recent years. We have investigated phase behavior, gelation, rheology, and structure of modified versions of the water-soluble copolymer of type PEO-PPO-PEO (Pluronic, F127) with short (PCL(5)) or long (PCL(11)) poly(caprolactone) blocks at both ends. By visual inspection of the studied semidilute and concentrated polymer samples at various temperatures, gelation and phase separation could be mapped and the length of the PCL blocks had a strong impact on the observed features. By using oscillatory shear experiments, the gel points of the systems were determined and an interesting anomaly of the complex viscosity was observed at high frequencies where the moieties were kinetically arrested. This irregularity was strengthened for the PCL(11) copolymer and this was ascribed to bridging of the micelles due to the long PCL blocks. The mesoscopic structure of the systems was studied by using small angle neutron scattering. The position and amplitude of the observed correlation peak, which discloses vital intermicellar correlations in the scattering function depends on temperature, concentration, and the length of the PCL blocks. Frequently the scattering function could be portrayed by a spherical core-shell micelle model with hard sphere interaction between them. The estimated aggregation number (Nagg) was substantially affected by the PCL content of the polymer and a significant influence of polymer concentration and temperature on the value of Nagg was found.

Physical gelation of AB-alternating copolymers made of vinyl phenol and maleimide units: cooperation between precisely incorporated phenol and long alkyl pendant groups

Alternating copolymers of vinyl phenol and alkyl maleimide gave organogel in aromatic solvents. The gelation was induced by segregation.

Luminescent lanthanide (Eu(iii)) cross-linked supramolecular metallo co-polymeric hydrogels: the effect of ligand symmetry.

Two lanthanide luminescent naphthyl-dipicolinic amide (dpa) methacrylate monomers for the synthesis of grafted supramolecular co-polymer gels (hydrogels), and their use as additional crosslinks in robust covalently cross-linked HEMA hydrogels is presented; the results demonstrate the importance of the ligand symmetry for the Eu(iii) emission from the hydrogels.

Modification of Karaya gum by graft copolymerization for effective removal of anionic dyes

ABSTRACTA graft copolymer gel based on the ‘Karaya gum’ has been made by grafting Karaya gum (KG) with 2-(methacryloyloxyethyl)trimethylammonium chloride (METAC) via microwave irradiation technique. The swelling of the gel appeared to be a second-order kinetic process following Fickian diffusion. The material exhibited significant adsorption capacity for anionic dyes, namely, indigo carmine, methyl orange, Remazol brilliant blue R and Direct Black 38 from aqueous solution. The pseudo-first-order kinetic model and Freundlich isotherm models provided good correlation with the dye adsorption data on KG-g-PMETAC. Thermodynamic studies revealed the adsorption process to be endothermic in all cases.

Stretching PEO–PPO Type of Star Block Copolymer Gels: Rheology and Small-Angle Scattering

Cross-linked Tetronic star block copolymer gels, based on poly(ethylene oxide) and poly(propylene oxide), behave quite regular with respect to mechanical properties, but exhibits unusual absence of structural response to strain. The elastic response is linear up to more than 100% strain, with a steady-state modulus of the order of 0.01 MPa after an initial stress relaxation. Neutron and X-ray scattering experiments show a consistent but unexpected response to uniaxial strain, with no changes in characteristic molecular dimensions. Upon strain beyond about 100%, that is, when the stress-strain curve is no longer linear, structural texture appears and becomes even more pronounced upon further strain, thus, indicating alignment of the self-assembled hexagonally ordered cylindrical micelles with the cylinder-axis perpendicular to the strain. It is proposed that the main structural response to large-amplitude strain is related to a layer-dominated structure of cross-linked star molecules.

Precision polymer network science with tetra-PEG gels—a decade history and future

Tetra-PEG gels, near-ideal polymer networks prepared by cross-end-coupling of A and B tetra-functional poly(ethylene glycol) (PEG) prepolymers having complementary end groups, were first fabricated in 2008. Comparisons of the mechanical properties with those of theoretical predictions indicate negligible fractions of defects and/or entanglements. Small-angle neutron scattering profiles of Tetra-PEG gels are very similar to those of the corresponding polymer solutions, suggesting negligible inhomogeneities originated from cross-linking. Due to the remarkable mechanical properties, extremely low structural inhomogeneities, and biocompatibility, tetra-PEG gels have gathered much attention since its discovery. The number of citation of Tetra-PEG gels is now over 2700 and is still growing rapidly. Chemical reaction kinetic studies also show a high degree of cross-linking reaction and its tunability, which leads to an idea of cross-linking probability tuned (p-tuned) networks. Versatility of the cross-coupling reactions allows us to prepare not only hydrogels but also organogels and ion gels, copolymer gels, non-stoichiometric gels, and so on. A decade history of the Tetra-PEG gels is reviewed with a variety of potential applications encompassing multiresponsive systems.

Ionic liquid-immobilized polymer gel electrolyte with self-healing capability, high ionic conductivity and heat resistance for dendrite-free lithium metal batteries

High-energy rechargeable lithium metal batteries have attracted soaring attention because of high specific capacity and low electrochemical potential of lithium metal. Unfortunately, the lithium dendrite growth upon Li plating severely hinders its practical application. Herein, we report the preparation of ionic liquid (IL) immobilized polymer gel electrolytes with strong ion-dipole interactions between imidazolium-based IL and fluorinated copolymer gel for stable and dendrite-free Li+ plating/stripping. The adoption of IL leads to the formation of a tightly cross-linked gel framework with tethered anions, providing greatly-improved mechanical strength, good heat resistance, favorable self-healing capability, high ionic conductivity, and a stable electrochemical window up to 4.5 V vs. Li+/Li that can satisfy the demand of high-voltage cathodes. The membrane of IL-immobilized polymer gel electrolyte enabled dendrite-free Li deposition, showing stable cycling durability for 1000 h at 0.5 mA cm−2, and the functional mechanism was carefully investigated. By coupling with this gel electrolyte membrane, the LiFePO4/Li cell exhibit much superior cycling stability and rate performance. Moreover, the lithium-sulfur batteries assembled with the IL-immobilized polymer gel electrolyte also show efficient suppression of polysulfide shuttling and self-discharge, bringing high specific capacity and long cycling life.