Liquid crystalline surface tension and radius dependence of the internal pressure in liquid crystalline bubbles and droplets

The balance of surface momentum density is the equation relevant to describ e capillary rise experiments as well as the radius-internal pressure relati on in l quid crystalline bubbles and droplets. This equation involves the s urface stress tensor. The surface stress tensor has been calculated from th e Second Law of Thermodynamics. The normal stresses do not vanish. They hav e an influence in capillary rise experiments for measuring the surface tens ion: For simple liquids the easiest way to measure the surface tension is t he determination of the hight of the liquid in a capillary and the contact angle of the liquid at the glass surface. In the case of simple liquids the re is an algebraic relation between these quantities and surface tension. T his is not the case for liquid crystals. There one has a differential equat ion relating surface tension to the measured quantities. This results in an influence of boundary conditions. Also the pressure-radius relation for sm ectic bubbles is predicted to be different from the relation for simple mat erials.