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 describe capillary rise experiments as well as the radius-internal pressure relation in liquid crystalline bubbles and droplets. This equation involves the surface stress tensor. The surface stress tensor has been calculated from the Second Law of Thermodynamics. The normal stresses do not vanish. They have an influence in capillary rise experiments for measuring the surface tension: For simple liquids the easiest way to measure the surface tension is the 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 there is an algebraic relation between these quantities and surface tension. This is not the case for liquid crystals. There one has a differential equation relating surface tension to the measured quantities. This results in an influence of boundary conditions. Also the pressure-radius relation for smectic bubbles is predicted to be different from the relation for simple materials.