Transport properties of glass-forming liquids suggest that dynamic crossover temperature is as important as the glass transition temperature.

ABSTRACT: It is becoming common practice to partition glass-forming liquids into two classes based on the dependence of the shear viscosity ? on temperature T. In an Arrhenius plot, ln ? vs 1/T, a strong liquid shows linear behavior whereas a fragile liquid exhibits an upward curvature [super-Arrhenius (SA) behavior], a situation customarily described by using the Vogel-Fulcher-Tammann law. Here we analyze existing data of the transport coefficients of 84 glass-forming liquids. We show the data are consistent, on decreasing temperature, with the onset of a well-defined dynamical crossover ?(×), where ?(×) has the same value, ?(×) ? 10(3) Poise, for all 84 liquids. The crossover temperature, T(×), located well above the calorimetric glass transition temperature T(g), marks significant variations in the system thermodynamics, evidenced by the change of the SA-like T dependence above T(×) to Arrhenius behavior below T(×). We also show that below T(×) the familiar Stokes-Einstein relation D/T ? ?(-1) breaks down and is replaced by a fractional form D/T ? ?(-?), with ? ? 0.85.

SUBMITTER: Mallamace F 

PROVIDER: S-EPMC3012472 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature