PERCOLATIVE ASPECTS OF VISCOUS FLOW NEAR THE GLASS TRANSITION

Abstract

Jumps in e.g.“equilibrium” specific heats, ∆C at the glass “transition”, Tg are kinetic. The upward curvature of log viscosity, η, vs 1/T supposedly indicates a phase transition at T0<Tg because the functional form fitting data over the largest temperature range diverges at (an inaccessible) T0. But the strongest curvature of η is near Tc, often 50K above Tg; it marks a cross-over from diffusive (T>Tc) (treated in effective-medium theories) to percolative transport (T<Tc). The pressure, (P), dependence of Tg, correlations of Tg with T0 and the melting temperature, Tm, (mixed) applicability of Ehrenfest theorems to dTg/dP, decoupling of mechanical and dielectric relaxation at Tc (measured by Rd, the ratio of mechanical and dielectric relaxation times), correlation of non-exponentiality in dielectric relaxation with Rd, dependence of Tg on system size, relative rates for shear and bulk moduli, and shapes of dielectric and specific heat relaxations can be described. Possibly the correlation of the Kauzmann temperature, TK, with T0 is also explicable using percolation. TK marks coincidence of extrapolated “configurational” entropies of super-cooled liquids with corresponding crystals. The physical basis for these results in a relevance of short-range inhomogeneities (which “average out” over large distances) removes a need to consider an underlying phase transition.