Stimuli-responsive gels undergo macroscopic changes when exposed to external stimuli, which makes them ideal for developing adaptive chemical reactors. Early investigations into hydrogels revealed that crosslinked polymer networks undergo reversible volume phase transitions, where temperature, pH and solvent composition govern the dynamics of swelling and shrinking. While the behaviour of hydrogels in aqueous environments has been well characterised, lyogels incorporating organic solvents have received comparatively little attention, despite their potential to enhance chemical compatibility and functional versatility.
In this collaborative study, the researchers from four different institutes at TUHH investigate how solvent polarity and crosslinking density influence the swelling behaviour, pore formation and molecular-scale dynamics of poly(N-isopropylacrylamide)-based lyogels. Through a combination of swelling measurements, scanning electron microscopy and multiscale nuclear magnetic resonance (NMR) relaxometry and diffusometry, they demonstrate that solvent polarity fundamentally alters lyogel structure and dynamics. Lyogels swollen in a high-polarity solvent exhibit 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 could be used to tailor lyogels for use in dynamic environments, with potential applications in adaptable and tunable chemical reactors.
Muhammad Adrian, Kathrin Marina Eckert, M. Raquel Serial, Artyom Tsanda, Lukas Rennpferdt, Stefan Benders, Hoc Khiem Trieu, Tobias Knopp, Irina Smirnova, Alexander Penn (2026). NMR relaxometry probes solvent-polarity-dependent molecular interactions in stimuli-responsive lyogels. Phys. Chem. Chem. Phys., Advance Article.
