Viscosity and Glass Transition Temperature of Aqueous Mixtures of Trehalose with Borax and Sodium Chloride

Abstract

The glass transition temperature (Tg) and viscosity of aqueous trehalose and its mixtures with either NaCl or Na2B4O7 (borax) have been measured over a wide range of concentration. Borax and sodium chloride increase the viscosity and Tg‘ of aqueous trehalose. Although the presence of ionic charges may partly explain some of the observed effects, it is clear that ionic solutes that form complexes with trehalose lead to a greater increase in Tg. The viscosity of supercooled aqueous mixtures was measured at several temperatures, most of them above the so-called crossover temperature, Tg‘, where a change in the dynamics of relaxation processes is expected. The viscosities of all the binary and ternary mixtures exhibit the same temperature dependence when the temperature is scaled according to the Tg values; a change in the slope of the linearized WLF representation is observed at a temperature close to 1.2Tg. Above this temperature, a power law expression provides a similar description of the temperature dependence of viscosity as the WLF equation, the former having a physical justification in the mode coupling theory.