Empirical Determination of Pressure-Volume-Temperature-Entropy Equation of State of Polyethylene in Isothermal, Isobaric and Isochoric Ensembles

Abstract

An empirical pressure (P)-volume (V)-temperature (T)-entropy (S) equation of state (P-V-T-S Eos) of polyethylene (PE) has been determined based on the experimental data of P-V-T and isobaric heat capacity at 1 atm for PE. The thermodynamic quantities of P, V, T, and S fall into three ensembles which are an isothermal (T = const), isobaric (P = const), and isochoric (V = const) one and each ensemble has an intrinsic P-V-T-S Eos. Thermodynamic derivatives of and in the isobaric P-V-T-S Eos in the isobaric ensemble, the derivative of and in the isochoric P-V-T-S Eos in the isochoric ensemble and the in the isothermal P-V-T-S Eos in the isothermal ensemble have been evaluated over the temperature range of 293–343 K and pressure up to ∼1.0 GPa for PE. The P-V-T-S Eos in this work were checked by the Maxwell’s equations, such as and thermodynamic relations expressed by = and . The thermodynamic significance of the P-V-T-S Eos and the advantage of the P-V-T-S Eos over the P-V-T Eos are discussed.