NMR relaxometry probes solvent-polarity-dependent molecular interactions in stimuli-responsive lyogels

Abstract

Stimuli-responsive gels demonstrate macroscopic changes upon exposure to external stimuli, offering potential for the development of adaptive chemical reactors. Early investigations into hydrogels established that crosslinked polymer networks experience reversible volume phase transitions, with temperature, pH, and solvent composition governing swelling and shrinking dynamics. Although hydrogels behavior in aqueous environments has been extensively characterized, lyogels that incorporate organic solvents remain comparatively underexplored, despite their potential for enhanced chemical compatibility and functional versatility. Here, we investigate how solvent polarity and crosslinking density govern the swelling behavior, pore formation, and molecular-scale dynamics of poly(N-isopropylacrylamide)-based lyogels. Using a combination of swelling measurement, scanning electron microscopy, and multiscale NMR relaxometry and diffusometry, we demonstrate that solvent polarity fundamentally alters lyogel structure and dynamics. Lyogels swollen in a high-polarity solvent exhibits macroporous networks and slower solvent exchange rates, whereas a low-polarity solvent induces shrinkage, denser microstructures, faster solvent exchange rates, and stronger surface interactions. These results establish a mechanistic framework linking thermodynamic affinity, solvent dynamics, and microstructural confinement to macroscopic gel responsiveness. This framework provides guidance for tailoring lyogels in dynamic environments, with potential applications in adaptable and tunable chemical reactors.