TEMPERATURE AND CONCENTRATION DEPENDENCY ON EQUILIBRATION IN POLYSACCHARIDE ELECTROLYTE HYDROSOL

Abstract

ABSTRACT Polysaccharide electrolyte aqueous solutions were annealed in the sol state before gelation. The gel-sol transition temperature (Tg-s) was determined by the falling ball method (FBM). It was found that Tg-s shifted to the high temperature side after annealing, and the equilibrium value increased with the increase of the concentration of the solution and the annealing temperature. This fact suggests that the structure which induces the gelation is formed when the system is annealed in the sol state. By differential scanning calorimetry (DSC), the melting enthalpy (Δ Hm) of the system was measured. Δ Hm increased in the initial stage of annealing, showing a varied oscillation pattern and then approached a constant value. The rate of the change of Δ Hm increased with the increase of the annealing temperature. However, an obvious dependency on the concentration was not observed in the concentration region where the measurements were carried out. The anomalous behaviour of water was interpreted as the adsorption and desorption of water restrained by polysaccharide molecular chains. It is thought that the molecular assemblies of polysaccharide chains dissociate in the above process, and following this the system was subsequently homogeneous. The phenomenological equation describing the anomalous behaviour of water was derived. Temperature and concentration dependency of the structure formation in the annealing process is discussed based on the derived equation.