Rheo-Impedance Measurements for the Evaluation of Thermoresponsive Polymer Gels

Although various thermoresponsive properties of poly(N-isopropylacrylamide) (PNIPAM) hydrogels have been investigated during phase transitions, the effects of the changing gel structure on the electrochemical properties of PNIPAM gels are poorly understood. Therefore, this study uses rheo-impedance measurements under simultaneous temperature modulation and shear deformation to examine the mechanism governing the conductivity of these gels. The impedance spectra of the PNIPAM hydrogels exhibit a distinct transition near the lower critical solution temperature, indicating that the internal conductive pathways dynamically reconstruct, associated with gel deswelling. Meanwhile, the nonlinear behavior of the impedance response with the varying shear rate suggests shear-induced degradation of the gel structure, followed by conductive network reformation. These results highlight the strong correlation between the internal microstructure of the hydrogel and its electrochemical properties, thus demonstrating the effectiveness of rheo-impedance analysis in determining the coupled mechanical-electrical responses of stimuli-responsive soft materials. Unlike conventional static measurements, this approach enables dynamic in situ evaluation of functional transitions within hydrogels. This study provides new insights into the design and analysis of intelligent hydrogel systems, with potential implications for soft actuators, and establishes a methodological foundation for extending rheo-impedance analysis to other responsive polymer systems, thereby broadening its applicability in smart material research.