Conductivity of maltose–water–KCl mixtures in the supercooled liquid and glassy states

Abstract

The conductivities of low water content amorphous maltose–water–KCl mixtures have been measured using both direct current and alternating current techniques at temperatures ranging from –60 °C to 85 °C. The mixtures all contained 11.6% w/w water and between 0.0052% w/w and 0.52% w/w KCl which resulted in mixtures with a calorimetric glass-transition temperature, T_g, of –5 °C. In the supercooled region, as the temperature is reduced to T_g, the activation energy of the conductivity increases from 80–85 kJ mol^–1 to 155–165 kJ mol^–1 and the conductivity is found to depend upon the viscosity to the power –0.52, which indicate that the conductivity is uncoupled from the viscosity. In the glassy region, as the temperature is reduced below T_g, the conductivity falls at a reduced rate with an activation energy of 60–75 kJ mol^–1, a value which is similar to the activation energy of the secondary dielectric relaxation process in the glass. Qualitatively similar conductivity behaviour has been observed in other classes of amorphous materials, such as polymers and ionic glasses. The ability of conduction measurements to probe translational mobility in supercooled and glassy states makes it suitable for investigating the effects of molecular structure and size on mobility.