Semiempirical examination of the van der Waals and Tonks models for polymers and simple liquids

Abstract

Semiempirical examination of the van der Waals and Tonks models for polystyrene and polyisobutylene polymers and the simple liquids n-heptane, benzene and carbon tetrachloride has been done using an empirical equation derived from the thermodynamic equation of state and experimental data for the thermal pressure coefficient γ v , molar volume V and heat capacity C v at constant volume. The equation derived for internal energy is expressed as E = (γ vT − P)(V − V 0) + 3RT 2 and is found to be useful in determining the internal energy of polymers and simple liquids, where V 0 is a constant volume. The internal energy function has strong correlations with internal energy for the van der Waals model and with entropy for the Tonks model. It is discussed through comparisons of our internal energy function with other models whether the van der Waals and Tonks models are the best ones to use or not.