Strength and salt/pH dependent-sorption capacity modulation of N-(alkyl)acrylamide-based semi-IPN hybrid gels reinforced with silica nanoparticles

Smart Crowding on pH-Induced Elasticity of Weakly Anionic poly(N-Isopropylacrylamide)-Based Semi-Interpenetrating Polymer Networks via Integration of Methacrylic Acid and Linear Polyacrylamide Chains

Weakly anionic semi-interpenetrating polymer networks (semi-IPNs), comprised of copolymer poly(N-isopropylacrylamide-co-methacrylic acid) P(NIPA-MA) and linear poly(acrylamide) (LPA) chains as macromolecular crowding agent, are designed to evaluate pH-induced swelling and elasticity. Uniaxial compression testing after swelling in various pH-conditions is used to analyze the compressive elasticity as a function of swelling pH and LPA-content. The swelling of P(NIPA-MA)/LPA semi-IPNs is strongly pH-dependent due to MA units incorporated into the copolymer network which already exhibits temperature-sensitivity by presence of PNIPA counterpart. Since the behavior of semi-IPNs is a combination of PMA, LPA, and PNIPA moieties, the sensitivity of swelling to external pH can be modified with increasing swelling temperature. At high pH conditions, LPA-doped semi-IPNs show elasticity representing soft and loosely cross-linked structure. Elastic modulus is higher in acidic pH condition due to the less swelling tendency, while in basic pH, the modulus decreases significantly in coordination with swelling. Oscillatory swelling reveals how fast semi-IPNs can respond to environmental pH change (2.1-10.7). By describing adsorption potential of semi-IPNs for cationic methylene blue uptake by pseudo-first-order and Freundlich model, the designed poly(NIPA-MA)/LPA semi-IPNs emerge as promising smart materials in applications requiring rapid response to changes in temperature and pH via diffusional properties.

Anionic starch-based hybrid cryogel-embedded ZnO nanoparticles: tuning the elasticity and pH-functionality of biocomposites with dicarboxylic acid units

Weakly anionic semi-interpenetrating polymer network (semi-IPN) biocomposites based on starch (ST)-incorporated poly(acrylamide-co-itaconic acid)/ZnO (ST-PAI/ZnO) were synthesized by a simple one-pot method via free radical aqueous polymerization. Hybrid biocomposites exhibited lower equilibrium swelling compared with neat copolymer gel. For both hydrogels and cryogels, swelling followed a decreasing order as copolymer PAI > starch-free PAI/ZnO > ST-PAI/ZnO gels. With the addition of 9% ST and ZnO, the swelling ratio of gels decreased from 898 to 68.3, resulting in a significant increase in elastic modulus. Compared with a fixed amount of ST, biocomposite cryogels exhibited significantly higher modulus than hydrogels. With the addition of 9% ST, the elastic modulus of cryogels reached 22.2 kPa while it was 2.7 kPa for the hydrogels. An equation expressing the effective cross-linking density of semi-IPNs presented by a cubic polynomial as a function of starch was obtained. As pH increased with the presence of dicarboxylic acid units, a gradual increase in swelling occurred at two different pH values. A gradually reproducible swelling change of semi-IPNs was depicted with pH ranging from 2.1 to 11.2. Biocomposite cryogels showed rapid swelling in a buffer solution of pH 11.2 and rapid shrinking in pH 2.1. Salt-induced swelling testing showed that the ability to reduce the degree of swelling and solubility of starch was Br- > Cl- > NO3- > SO42- for anions consistent with the Hofmeister series. Adsorption efficiency for the removal of methyl violet (MV) dye was analyzed using Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm models. The results confirmed that the Langmuir isotherm and pseudo-second-order model are suitable for describing MV adsorption on semi-IPN biocomposites. The synthesized biocomposites with good swelling/deswelling kinetics in different pH-buffer solutions, high saline absorbency, desirable adsorption efficiency, and acceptable pH-dependent swelling reversibility can be considered as smart hybrid materials for the adsorption of the dye in water purification tasks.

Interpenetrating polymer networks for desalination and water remediation: a comprehensive review of research trends and prospects

Interpenetrating polymer network (IPN) architectures have gained a lot of interest in recent decades, mainly due to their wide range of applications including water treatment and environmental remediation. IPNs are composed of two or more crosslinked polymeric matrices that are physically entangled but not chemically connected. In polymer science, the interpenetrating network structure with its high polymer chain entanglement is commonly used to generate materials with many functional properties, such as mechanical robustness and adaptable structure. In order to remove a targeted pollutant from contaminated water, it is feasible to modify the network architectures to increase the selectivity by choosing the monomer appropriately. This review aims to give a critical overview of the recent design concepts of IPNs and their applications in desalination and water treatment and their future prospects. This article also discusses the inclusion of inorganic nanoparticles into traditional polymeric membrane networks and its advantages. In the first part, the current scenario for desalination, water pollution and conventional desalination technologies along with their challenges is discussed. Subsequently, the main strategies for the synthesis of semi-IPNs and full-IPNs, and their relevant properties in water remediation are presented based on the nature of the networks and mechanism, with an emphasis on the IPN membrane. This review article has thoroughly investigated and critically assessed published works that describe the latest study on developing IPN membranes, hydrogels and composite materials in water purification and desalination. The goal of this critical analysis is to elicit fresh perspectives regarding the application and advantages of IPNs in desalination and water treatment. This article will also provide a glimpse into future areas of research to address the challenges relating to advanced water treatment as well as its emerging sustainable approaches. The study has put forward a convincing justification and establishes the relevance of IPNs being one of the most intriguing and important areas for achieving a sustainable generation of advanced materials that could benefit mankind.

Anionically modified N-(alkyl)acrylamide-based semi-IPN hybrid gels reinforced with SiO2 for enhanced on-off switching and responsive properties

Semi-interpenetrated (semi-IPN) poly(N-isopropylacrylamide-co-methacrylic acid)/polyacrylamide P(NIPA-MA)/PAAm hybrid gels containing linear poly(acrylamide) PAAm chains were designed by incorporation of different amounts of silica particles (SiP). Formation of temperature-sensitive semi-IPN hybrid gels was evaluated by simultaneous radical polymerization under different polymerization temperatures, and the effect of polymer/particle interfaces on the swelling and elasticity was explained. Nanoparticle-mediated enhancements were studied to understand the effect of addition of SiP to anionically modified semi-IPNs. Hybrid network formation was confirmed by FTIR, with an increase in SiP resulting in an increased Si-O-Si absorption peak in hybrid samples. P(NIPA-MA)/PAAm/SiP gels showed a reduction in the degree of swelling with the addition of SiP. The Flory-Huggins interaction parameter of the semi-IPN hybrid-solvent was estimated using the extended equation. The compression test results showed an improvement in the stiffness and modulus attributed to stress transfer from the hybrid network to nanoparticles. Swelling processes of semi-IPN hybrids prepared by cold polymerization have anomalous diffusion owing to polymer relaxation, while Fickian behavior was observed for the hybrids obtained by warm polymerization. During oscillation shrinking-swelling of semi-IPN hybrids upon ionic-strength switching in NaCl solutions, the gels retained their shape and integrity for 10 cycles of testing. To evaluate the adsorption characteristics of semi-IPN hybrids, methyl violet (MV) was chosen as a model cationic dye. The effects of contact time, silica content and initial dye concentration were studied and the time-dependent adsorption data were fitted with six kinetic models. The MV uptake capacity of semi-IPN hybrids increased with an increase in the initial MV concentration as well as with silica content. The adsorption process followed pseudo-second order type adsorption kinetics and the mechanism of process was better described by intraparticle diffusion. These results will contribute to the understanding of roles of anionic comonomer and linear polymer doping in nanoparticle-mediated synthesis of hybrid gels and to the development of next-generation materials for pharmaceutical and environmental-based applications.