The surface (interfacial) tension of polymer melts is an important thermodynamic parameter that plays a key role in many technological processes such as wetting, coating, polymer blending, and the reinforcement of polymers with fibers. In the past, the precision of drop shape methods to determine the surface tension of polymer melts was strongly dependent on the measurement of some selected critical points of the drop shape, which had to be interpreted using different sets of tables. By means of these classical calculation procedure, accurate and consistent results are difficult to obtain. Recent developments utilize video digital image processing techniques to extract the entire experimental drop profile with subsequent numerical procedures to calculate the surface (interfacial) tension based on the Laplace equation of capillarity. By employing a new strategy, we could show that axisymmetric drop shape analysis (ADSA) can be used to determine simultaneously the surface tension and the density of polymer melts. To achieve this, two developments were necessary. First, the ADSA algorithm had to be modified. 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.

ADSA an approach started by Rotenberg et al. unifies the methods both of sessile drops and of pendant drops. ADSA requires the local gravity, the densities between the liquid and fluid phases and several arbitrary but accurate coordinate points selected from the drop profile as input parameters. However, the determination of the density of a polymer melt is not a trivial task. Additional time-consuming dilatometry measurements are necessary. Therefore, the ADSA algorithm was modified in such a way that the density would be replaced by the mass of the drop as input parameter. Conceptually, this is readily feasible, since the ADSA algorithm also yields the volume, so that the density will become output rather than input. From the experimental perspective, use of a sessile drop rather than a pendant drop was required, since the mass of a sessile drop is easily available through weighing the polymer granulate before or after the experiment. In this way, surface tension and density of polymer melts can be determined simultaneously by analyzing the shape of a sessile drop.