Surface Tension Measurement of Polystyrene Melts in Supercritical Carbon Dioxide

This paper introduces an experimental method that uses Axisymmetric Drop Shape Analysis-Profile (ADSA-P) to measure the surface tension of polymer melts in supercritical carbon dioxide. The method is verified by experiments in air and nitrogen, where reproducibility tests and statistical analyses are performed. The surface tension of polystyrene (PS) melts in supercritical carbon dioxide is obtained, while the gas solubility is correlated with the surface tension value determined under various pressures. The Sanchez-Lacombe (S-L) equation of state (EOS) is applied to estimate the pressure-volume-temperature (PVT) data of the PS/supercritical-carbon-dioxide mixtures, which gives density data. The relationship between surface tension and density is described by the empirical Macleod equation. To characterize the stability of pendant drops formed by the polymer melt, the Bond number is determined to be useful; in particular, a stable pendant drop is obtained when the Bond number is in the range of 0.4-0.8.