Dielectric relaxation of interfacial polarizable molecules in chitosan ice-hydrogel materials

Abstract

The functionalities of hydrogel-based smart materials are highly related to the electrostatic interactions and molecular polarization associated with the polymer networks and encapsulated water droplets, and therefore the dielectric responses of the polarizable molecules in the polymer, water, and polymer-water interfaces are particularly attractive, where the properties of polymer-water interfacial molecules remain elusive. Different from extensive dielectric relaxation spectroscopy studies on polymer hydrogel solutions, in this work we investigate the dielectric response of chitosan hydrogels below the water solidifying point (ice-hydrogels) so that the contribution of chitosan-water interfacial molecules can be isolated. It is revealed that the chitosan-water interfacial polarizable molecules have slow dielectric relaxation but large polarization compared with the chitosan chains and water molecules, and the dielectric relaxations beyond ∼104 Hz are substantially weak. The thermal activation energy of the dielectric relaxation for these interfacial polarizable molecules can be as large as 0.93 eV, i.e. 89.73 kJ/mol. The present work provides a platform for characterizing the polymer-water electrostatic interactions and interfacial polarizable molecules, informative to understand the microstructure-property relationships of chitosan-based hydrogel materials.