Controlled synthesis of ternary acrylamide/sodium acrylate/polyethyleneglycol hybrids by integrating different clays and fillers: a comprehensive evaluation of structural features

Abstract

A series of anionic poly(acrylamide-co-sodium acrylate)/poly(ethylene glycol), PAN/PEG, hybrids were conveniently synthesized via free radical aqueous polymerization by integrating bentonite, kaolin, mica, graphene and silica, following a simple and eco-friendly crosslinking methodology. A comparative perspective was presented on how integrated nanofillers affect the physicochemical properties of hybrid gels depending on the differences in their structures. Among the five types of nanofillers, bentonite-integrated hybrid gel had the highest water absorbency, while graphene-integrated gel had the lowest. The elastic moduli of hybrid gels with the same content of inorganic component followed the order graphene > silica > mica > kaolin > bentonite. Adding 1.50% (w/v) bentonite to the PAN/PEG matrix increased the elastic modulus by 1.4 times compared to the as-prepared state, while adding the same amount of graphene created a 4.1-fold increase. By decreasing the synthesis temperature of hybrids to cryoconditions, −18 °C, an increase in the modulus of all gels was observed, while the modulus of graphene-doped gels increased from 25.9 kPa to 39.1 kPa. pH-dependent swelling demonstrated that hybrid gels can dynamically bind or release protons in response to changes in surrounding pH and thus abruptly change their overall dimensions. On–off switching behavior as reversible pulsatile swelling in pH 11.2 and deswelling in pH 2.1 showed that hybrid gels exhibit reversible pH-responsiveness following Fickian diffusion of water into the hybrid matrix. The change in pH of the swelling medium caused a 4.5-fold increase in swelling ratio for the silica-doped hybrid gels. The studies in which anionic hybrids were tested to explore adsorption potential for cationic dye methylene blue (MB) showed that adsorbent properties could be tuned to the desired extent by incorporating different fillers. In terms of efficiency among the selected fillers, the maximum efficiency for MB was obtained as 99.2% and 88.60% for hybrids containing graphene and silica, respectively. The adsorption of MB on hybrids was fit to the three-parameter Sips model rather than the two-parameter models. The results introduced a new perspective on the design of ternary hybrid gels that could effectively address both the mechanical and responsive properties of soft materials, providing a platform for subsequent cationic dye adsorption.