THE PRINCIPLE OF CORRESPONDING STATES FOR POLYMER LIQUID SURFACE-TENSION

A corresponding states principle is demonstrated for polymer and oligomer liquids. Scaling the measured surface tension with the thermodynamic properties obtained from pressure, volume, and temperature (PVT) data, one obtains a universal curve. We have developed a discrete interface cell model (DICM), which is a modified form of the Prigogine-Saraga cell model theory of surface tension which had previously been applied to polymer liquids. Using PVT data as input, the model accurately describes the surface tension data. With no adjustable parameters, the DICM theory provides a simple predictive tool for the conversion of the PVT properties of any material into surface tensions, with high accuracy at all temperatures and molecular weights. A strict adherence to the corresponding states principle is observed within each oligomer-to-polymer homologous series. This allows the model to predict the surface tension to within 1% accuracy for such a homologous series. The existence of a strict corresponding states principle implies that for the polymers studied here, the dominant contribution to the surface tension comes from the cohesive and entropic properties of the bulk liquids and is only weakly dependent on the molecular conformations and end groups. A discussion of the experimental difficulties in obtaining accurate PVT data and also extrapolating the thermodynamic properties to atmospheric pressure is given.