How do smectic layers interact at large distances? Theory of Long-Range Interactions in Smectic Liquid Crystals Philip Taylor, Case Western Reserve University, Cleveland, Ohio 44106 How do smectic layers interact at large distances? Three-layer repeat Four-layer repeat Smectic liquid crystals can exist in forms in which the orientation of the molecules rotates helically as one moves from layer to layer. The mechanism responsible for the formation of helical structures is not understood. We have developed an analytical theory of the inter-layer interactions that can arise from thermal fluctuations in the smectic layers. Just as in a sheet of plywood, the orientation of the grain affects the strength of the material, the relative orientation of the smectic layers affects the free energy The simulation shown on the left illustrates the alignment of molecules in a smectic sample. Our remaining task is to incorporate the adjacent layer interactions, which are steric in nature, into the larger picture involving the long-range interactions due to thermal fluctuations.