Semiempirical equation of state for polymers and simple liquids under high pressure

Abstract

The semiempirical equation of state for polymers polyethylene (PE), poly( n-butyl methacrylate) (PNBMA) and polystyrene (PS) for pressures up to 2 kbar, five hydrocarbons from n-heptane to n-octadecane over 0 to 1.2–9.0 kbar, five organic liquids, including carbon tetrachloride (CCl 4), over 0 to 2.0–12.0 kbar, water up to 10 kbar and argon up to 3 kbar has been derived by using experimental data for specific volume V, compressibility β T and thermal expansion coefficients α P under high pressure published by Simha et al., Hellwege et al., Bridgman, Streett and others on the basis of the homogeneous function approach. The equations derived in this work under a constant temperature are: ln V∼-(P+P 0) 1-m 0 β T∼(P+P 0) -m 0 α P∼(P+P 0) 1-m 0 where P 0 is a constant with respect to pressure but depends on temperature, and m 0 and n 0 are constants determined from the experimental data. Values of m 0 range from 0.76 to 0.99, with an average value 0.87 for polymers and simple liquids including water and argon, while values of n 0 for α P for argon are around 0.50 over 90–150 K.