SURFACE TENSIONS OF LIQUID-CRYSTALLINE AND ISOTROPIC POLYMER MELTS

The surface tensions (gamma) of a branched polyethylene and two side-group luquid-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 gamma 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.