Relaxation and diffusion-viscosity decoupling in supercooled and glassy polyol aqueous solutions

M. P. LONGINOTTI; J. TREJO GONZALEZ; J. GELMAN CONSTANTIN; H. R. CORTI

Roma, Italia

Congreso; 6th International Discussion Meeting on Relaxations in Complex Systems; 2009

Tracer and self-diffusion have been widely studied in one component supercooled liquids [1,2]. However, few studies have been performed in more complex systems, such as water-polyol mixtures, which are the most interesting systems for technological applications, such as cryopreservation. In this work we have analysed the diffusion viscosity dependence of ionic and neutral solutes in supercooled sucrose, trehalose and glycerol aqueous solutions, along with the dielectric relaxation in related systems. We meassured the molar conductivity of several electrolytes and the diffusion of ferrocene-methanol, using electrochemical techniques, over a wide viscosity range. It was observed that for the ionic solutes: NaCl, KCl, CsCl, Bu4NBr and MgCl2, the molar conductivity viscosity dependence cannot be described by the classical hydrodynamic model (Walden Rule) well above the glass transition temperature (Tg) [3]. This behaviour was explained by the presence of structural microheterogeneities in the solution.The diffusion of the neutral probe in supercooled sucrose and glycerol aqueous solutions was well described by the classical hydrodynamic model (Stokes- Einstein equation) at small Tg/T values, while close to Tg diffusion decouples from viscosity. The critical temperatures at which diffusion decouples from viscosity were compared with the temperatures at which a and b relaxation processes bifurcate.