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What promotes smectic order: Applying mean-field theory to the ends
David A King1, Randall D Kamien1
1Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, Pennsylvania 19104, USA.
Abstract:
Not every particle that forms a nematic liquid crystal makes a smectic. The particle tip is critical for this behavior. Ellipsoids do not make a smectic, but spherocylinders do. Similarly, only those N-CB alkylcyanobiphenyls with sufficiently long (N≥8 carbons) alkane tails form smectics. We understand the role of the particle tip in the smectic transition by means of a simple two-dimensional model. We model spherocylinders by "boubas" with rounded tips, and ellipsoids by "kikis" with pointed tips. The N-CB molecules are modeled by a small body with a polymer tail. We find that rounded tips and longer polymer tails lead to a smectic at lower densities by making the space between layers less accessible, destabilizing the nematic.
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