The viscosities of three organic liquids, salol, α-phenyl-o-cresol, and o-terphenyl, have been measured over a wide range of temperature using falling-sphere and bending-beam viscosimeters. The heat capacity vs. temperature relations for each of these materials have also been determined for the glass, liquid, and crystalline states, as have the thermal expansion coefficients of glassy and liquid α-phenyl-o-cresol. For none of the liquids investigated can the flow behavior over the full range of measured viscosity be adequately represented by any of the standard theoretical models. The agreement between molecular dynamics calculations and a modified free volume theory is combined with the close description of flow at high temperature by a free volume model to suggest that free volume theories are most appropriately used to describe flow in the high-temperature region rather than in the region around the glass transition. It is also suggested that a second, easier flow process becomes dominant in the low-temperature region. Flow data on several classes of liquids may be correlated by means of a corresponding-states parameter. Although limitations are recognized for the use of any such normalization factor, the most satisfactory corresponding-states parameter for liquid viscosity seems to be the glass-transition temperature.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry