Surface tension obtained from various smectic free-standing films: The molecular origin of surface tension

High-resolution surface tension measurements have been carried out on the free-standing films of more than 30 selected liquid-crystal compounds in their smectic phases. Surface tension (g) values falling into major categories of 27, 24, 21, 13, and 11.5 dyn/cm have been obtained. The dependence of g on specific terminal groups or molecular structures will be discussed. Our results provide important information about the molecular origin of surface tension.