Viscosity prediction from a modified square well intermolecular potential model: polar and associating compounds

A theoretically based model for calculating both liquid and gas phase viscosities has been developed by modifying a statistical mechanics viscosity model based on the square well intermolecular potential. The original theory was corrected to account for the assumptions of only two-body interactions and molecular chaos for velocities and the inadequacy of the square well potential. In addition, the model was modified so that it approaches a consistent low density limit and to improve the dilute gas temperature dependence. The three model parameters are obtained from gas and liquid viscosity data and generalized with group contributions. With the resulting modified square well viscosity model, gas and liquid viscosities for a wide variety of over 100 polar and hydrogen bonding compounds are correlated with average deviations of 0.4% (gas) and 2.1% (liquid), and predicted with average deviations of 2.1% (gas) and 6.8% (liquid).