Simultaneous Determination of Surface Tension and Density of Polymer Melts Using Axisymmetric Drop Shape Analysis

By employing a new strategy, we show that axisymmetric drop shape analysis (ADSA) can be used to determine simultaneously the surface tension and the density of polymer melts from sessile drops at elevated temperatures. To achieve this, two developments were necessary. First, the ADSA algorithm had to be modified to replace the density by the mass of the drop as an input parameter. Since ADSA also yields the volume, the density became output rather than input. Second, a closed high-temperature chamber whose temperature could be precisely controlled and a sample holder that allowed the formation of highly axisymmetric sessile drops at elevated temperatures had to be developed. For a typical polymeric material (polystyrene), it is demonstrated that measurements with sessile drops yield essentially the same surface tension values and temperature coefficients as measurements with pendant drops. The densities determined with ADSA are comparable to independent PVT results. Copyright 1999 Academic Press.