Dendrite-like texture growth in the nematic liquid crystal phase of 4-n-heptyl- and 4-n-octyl-oxybenzoic acids aligned by a polyimide coating

Abstract

An oriented dendrite-like texture is reported, appearing at a definite temperature in the nematic phase range of 4-n-heptyl- and 4-n-octyl-oxybenzoic acids (HOBA and OOBA), aligned by rubbed polyimide and preceding the smectic C phase, on cooling. Two preferred directions with respect to the ‘easy’ axis are indicated in the dendrites grown of HOBA and OOBA. We discuss a possible mechanism, at molecular and supramolecular levels, for this dendrite growth; and assume that the building ‘blocks' of the dendrites are oligomers, or mixture of oligomers with ‘free’ closed and open dimers, constituting a detached crystalline layered state (named by us SmX, a smectic state intermediate between the N₁ ordinary nematic and SmC phases). The study of the dynamics of the dendrite growth demonstrates a scaling relationship typical for non-equilibrium systems. The observed dendrites can be considered as patterns formed in complex non-linear dissipative systems, driven outside of equilibrium.