INVESTIGATION OF THE STRUCTURE OF THE HILDEBRAND-SCATCHARD EQUATION BY USE OF THE PENG-ROBINSON EQUATION OF STATE

The origin of the double term difference (delta(1) - delta(2))(2) in t he solubility parameter delta, which is sometimes taken for granted by the polymer physicists in studies of the solubility of polymers, is i nvestigated in detail. The Peng-Robinson /1/ equation of state was tak en as the present state-of-the-art tool to perform this analysis. From the results of this study it follows that the power two in the expone nt of the delta difference (which is the result of geometrical averagi ng) does not seem to be correct. The error created by this interpretat ion is largest for mild interactions and for low molecular weight subs tances, but decreases either with the increase in molecular weight or with the presence of strong interactions within the system.