A modified cell model of monomeric and polymeric liquids

Abstract

An equilibrium model of liquids has been developed based upon the cell theory with a semiempirical cell partition function. With this model many of the thermodynamic properties of simple liquids are described by four characteristic parameters related to the molecular shape, size, and interaction energy. The average prediction errors when applied to 29 simple liquids over a wide range of temperature are 0.62% in the vapor pressure, 1.14% in the saturated volume, 1.24% in the heat of vaporization, and 1.78% in the thermal pressure coefficient. This model has been extended to polymeric molecules. With the molecular constants of the monomer, the P-V-T behavior of an amorphous or liquid polymer is shown to be predictable up to thousands of atmospheres over about a 200°C temperature range. The average errors in predicted specific volume are 0.70% for polyisobutylene, 0.30% for polyethylene, 1.35% for polystyrene, and 1.41% for the n-alkanes. The average error in predicted thermal pressure coefficient is 1.02% for polyisobutylene, 0.45% for polyethylene, and 1.81 % for the n-alkanes.