A VISCOSITY-TEMPERATURE RELATION FOR NEWTONIAN LIQUIDS

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Abstract
The lack of success of existing theories in describing viscosity of molecular liquids appears to be due to at least two difficulties. The mechanisms of viscous momentum transfer have not been identified, and the thermal motions of molecules can not be described until the spatial arrangement of molecules in a shearing liquid is known. This paper presents the results of an effort to identify the mechanisms of viscous momentum transfer. A model is proposed and a relation is derived from it that precisely fits viscosity data for a wide variety of Newtonian liquids. The effects of the spatial distribution of thermal motions and of intermolecule attraction are represented as parameters together with a Debye-like temperature. Values of these parameters are found from fitting the relation to published data. The parameters are found to be sensitive to molecular weight and to molecular configuration. Frequencies of interaction of molecules in the direction of the velocity gradient are of the order E 10 s −1. Abrupt shifts in these parameters with increasing temperature are found for paraffins at temperatures slightly above their melting points that are interpreted as disaggregation of molecules. Other abrupt shifts in the parameters at high temperatures for mercury and alcohol are interpreted as a change in the momentum transfer mechanism. Correlation of the parameters of the relation with molecular properties promises to provide predictive value. The relation provides a framework for further theoretical development.

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