Dynamics of confined ice and hydrated triple-helical polysaccharide, schizophyllan, in partially crystallized aqueous solution studied by dielectric spectroscopy

Abstract

This study investigates dielectric relaxation processes of partially crystallized aqueous schizophyllan solutions across a broad temperature (123–313 K) and frequency (10 mHz–10 MHz) ranges. Schizophyllan forms a triple-helix structure in aqueous solution. Through broadband dielectric spectroscopy, we identify three distinct dielectric relaxation processes: (1) a relaxation process of uncrystallized water restricted by schizophyllan, (2) a relaxation process of ice, and (3) a relaxation process involving the cooperative motion of hydrated schizophyllan and water, indicative of a hydrated-solute relaxation process in a partially crystallized polysaccharide solution. The relaxation time of the uncrystallized water process (process I) is nearly independent of the initial solute concentration over 10–45 wt%, indicating that its kinetics is governed primarily by the local binding environment. In contrast, the solute-related process (process III) shows convergence of relaxation times for initial concentrations above ∼30 wt%, which is consistent with ice crystallization driving the remaining uncrystallized phase toward a freeze-concentrated state of approximately fixed local composition; the initial concentration then mainly controls the phase fractions. Finally, the ice-related process does not exhibit the crossover commonly reported for bulk ice Ih within the explored temperature window. This crossover-free behaviour is consistent with restricted crystal growth and/or altered defect dynamics in ice formed in the polysaccharide matrix, although the crossover alone does not uniquely determine the microstructure of the crystallized ice.