Smectic Liquid Crystal Freely Suspended Films: Testing Beds for the Physics in Thin Membranes
Duong Hoang Nguyen, Joseph Maclennan
University of Colorado - Boulder
This thesis highlights the unique features of smectic liquid crystal freely suspended films to study surface effects and two-dimensional physics via three experiments: the first confirms the popular Saffman-Delbruck theory of the drag on a small cylinder in a thin membrane, the second measures the surface tension of a freely suspended molecular monolayer, and the third is a high-speed observation of the coalescence of two thin fluid disks. In the first experiment, we measure the diffusion constant of thicker domains (islands) in the film. They are perfectly circular and are readily observed under the microscope, making it possible to track the motion of their centers with high precision (~ 10 nm). In the second experiment, the imposed symmetry on a smectic monolayer helps to detect surface induced asymmetry on bilayer and thicker films via the motion of 1D interfaces between domains of different thicknesses. Lastly, in the third experiment, the high contrast of the film under reflection microscopy helps to capture the coalescence at high speed without introducing much noise at low light levels. Moreover, without the obstruction of any substrate, an optical trap can be effectively used to manipulate islands to force coalescence rather than having to wait for serendipitous events.