PATTERNS IN THIN LIQUID CRYSTAL FILMS AND THE DIVERGENCE (“SURFACELIKE”) ELASTICITY

Abstract

Thin submicron and micron films of liquid crystals placed between two isotropic media represent a particular example of confined systems. Such films can be prepared on the surface of glycerin or other liquids, In comparison with Langmuir monolayers, these films are macroscopically thick to involve the liquid crystalline order in the interplay between molecular structure and macroscopic organization. At the same time, the films are thin enough for such a strong competition between surface and bulk properties that transitional in-plane symmetry is spontaneously violated and a number of patterns appear: stripe domains, square lattices, strings, high strength defects and so on. We show that these structures are governed by the divergence (or “sufacelike”) K13 and K24 terms in the nematic free energy which have been ignored for decades. We also show that both terms can be included in the standard elasiticty theory without contradictions with the basic idea of the nematic phase. The one-dimensional confinement makes the films a unique object of investigation: although the phenomena observed are attributed to the vertical confinement, their manifestation is detected in a non-restricted film plane.