Empirical determination of equation of state for zero internal pressure in rare gas solids and semi-crystalline polymers

An equation of state for zero internal pressure in rare gas solids and semi-crystalline polymers has been determined based on the empirical functions of thermal pressure coefficient γV with respect to volume at constant pressure. The experimental data of PVT over wide range of temperature and pressure published by Anderson and Swenson and Syassen and Holzapfel for rare gas solids and Olabisi and Simha and Zoller for semi-crystalline polymers are used to evaluate γV. The function of γV with respect to volume determined at constant pressure is given by γ V = A { ( V − V 0 ) / V } ɛ ( V 0 / V ) 1 + c exp { − c ( V − V 0 ) / V } where V0 is the volume at 0 K, A, ɛ and c are constants. The function of internal pressure Pi = γVT − P with respect to temperature at constant pressure is determined by converting the function of γV(V) to a function of temperature γV(T). An empirical equation of state for zero internal pressure determined by pressure P∗, volume V∗ and temperature T∗ at which Pi = 0 is expressed by P ∗ V ∗ / R T ∗ = C ∗ − D ∗ V ∗ for rare gas and semi-crystalline polymer where C∗ and D∗ are constants. The practical meaning of the equation of state for Pi = 0 in the semi-crystalline polymers has been discussed.