The surface tensions (y) of a branched polyethylene and two side-group liquid-crystalline (lc) polyacrylates were measured in the isotropic, nematic and smectic states by the pendant-drop method. The surface tension vs. temperature characteristics of the lc polyacrylates studied show anomalous behaviour. The slope in the isotropic state is initially negative but changes its sign near the isotropic-nematic transition. The increase of y with decreasing temperature is regained in the nematic phase, until at the nematic-smectic transition the surface tension of the lc polymers discontinuously jumps to higher values and shows a very low temperature coefficient. The observed features have been found to be partly in agreement with the results of surface tension measurements on low-molar-mass liquid crystals, which indicates that the surface properties of the lc polymers are governed by the mesogenic side groups.

Surface tensions (γA) of two side group liquid‐crystalline (lc) polymethacrylates and the interfacial tensions (γAB) between the lc‐polymers (LCP) and branched polyethylen respectively polymethylmethacrylat were measured in the isotropic and nematic phase with the pendant‐drop method. The surface tensions vs. temperature characteristics show anomalous behavior. The slope is initially negative but changes its sign near the isotropic‐nematic transition. This behavior is in agreement with surface‐tension measurements on low‐molar‐mass liquid crystals from other authors. The interfacial tension mainly depends on the density difference Δρ between the two phases, at the phase‐transition so we observed a jump of the interface‐tension values and a change of the slope. The pendant‐drop apparatus contains a video image processing system, that allows to acquire the pendant‐drop profile with a personal computer. The program used to analyse the experimental data is based on the “robust‐shape method”. This algorithm allows to calculate both the surface‐tensions and the interface‐tensions respectively with a personal computer.