Transport in Supercooled liquids

H.R.CORTI; M.P LONGINOTTI

Experimental Thermodynamics. Vol IX

Royal Society of Chemistry

Año: 2014; p. 290 - 306

In Chapter 8 we focussed on recent advances in modelling and predicting the viscosity of dense fluids based on kinetic theory and on macroscopic considerations. In the present chapter we review other recent developments for dense fluids. We start with a fluid state that is at one extreme of molecular mobility and thus of considerable interest. Section 9.2 is focused on recent developments in the theory and modelling of supercooled liquids with special emphasis on water and aqueous binary solutions. Particular attention is paid to the importance of structural relaxation within the supercooled fluid. Understanding those relaxation processes is vital and leads to a number of different theoretical models including those proposed to explain the diffusion-viscosity decoupling, or put more simply the breakdown of the Stokes-Einstein relation. This is an interesting phenomenon, which indicates that in supercooled liquids, near the glass transition, the cooling process changes the nature of diffusional transport at the molecular scale. The developments described in the subsequent section, Section 9.3, take as their starting point the studies of the effect of pressure on the vitrification process. The observed density temperature scaling of transport and relaxation properties is extended to other thermodynamic regions and the relationships that describe transport properties in terms of residual entropy are discussed. The recent extensive testing of the proposed scaling laws is illustrated and their applicability to correlating the viscosity and self-diffusion of a large number of complex fluids is demonstrated. Section 9.4 is dedicated to a review of recent developments in the fundamental understanding and modelling of thermal diffusion; the Onsager phenomenon that leads to non-convective, compositional separation generated by thermal gradients. Recent work has led to elucidation of the processes that take place in various applications, ranging from isotope separation to estimating the connectivity of petroleum reservoirs and tracking seasonal changes in the historical, climatic records.