Viscoelasticity, morphology, and molecular diffusion in structurally controlled ternary poly(acrylic acid) and nonionic surfactant-based hydrogels

Hydrogels are among the most promising materials for biological applications mainly because of their ability to absorb large volumes of water and carry as well as deliver biologically active substances. A challenge is to make them appropriately responsive to environmental triggering factors simply and reliably. In this work, we present a basic approach of modification of a commonly used, low-cost poly (acrylic acid) – PAA – hydrogel with biocompatible surfactants regarding their possible thermoresponsive activity.Viscoelasticity, hydration, and molecular diffusion processes, in relation to the morphology of the hydrogel and its mixture with nonionic surfactant Brij 58, are studied systematically using oscillatory rheometry, NMR diffusiometry and imaging, and cryoSEM. Our results contribute to the understanding of interactions between weak PAA and nonionic surfactants. The changes of the hydrogel microstructure caused by nonionic and bio-safe surfactant or thermal induction are clearly reflected in their mechanical response as well as the translational mobility of water molecules entrapped within the hydrogel's network. The structural modification induced by adding nonionic surfactant gives rise to a decrease in hydrogel elasticity.