Temperature dependence of liquid viscosity

Least squares programs were used to evaluate the correlation between recent experimental results and theoretical, semi-theoretical, or empirical relations between liquid viscosity and temperature. It was found that none of these describes the experimental dependence in the whole range of temperature. A new dependence based on the free volume concept and cell-hole liquid theory is proposed. The theory permits linearization of the viscosity-temperature data in the range (Ti, Ti+1), where the Ti's are the liquid-liquid transition temperatures. It was demonstrated that these transitions, both in small molecular and in polymeric liquids, occur in discrete steps: Ti = aiTg, where Tg is the glass transition temperature and the ai's are numerical parameters. Not all the transitions Ti were apparent in all liquids. Transition T2 = 1.26Tg was observed for most polymeric liquids. On the basis of thermal analysis it was demonstrated that the Ti's coincide with the temperatures at which small changes in the apparent specific heat were detected. These temperatures can be assigned to the maximum rate of crystallization and melting temperatures of the metastable and stable crystalline forms.