A. Sugimura et al., ANOMALOUS ANCHORING EFFECT OF NANOPOLYIMIDE LANGMUIR-BLODGETT-FILMS IN A TWISTED NEMATIC LIQUID-CRYSTAL CELL, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 54(5), 1996, pp. 5217-5220
In a recent paper [Phys. Rev. E 52, 681 (1995)] we showed that in the
absence of an external field, the twisted structure of substrates with
weak anchoring can induce a deviation of the director at the surfaces
from the easy axis and that the anchoring energy can be evaluated by
measuring this deviation. To test the prediction, the anchoring energy
for nematic 4-pentyl-4'-cyanobiphenyl and polyimide Langmuir-Blodgett
(LB) substrates with thicknesses in a range less than 10 nm has been
measured. The anchoring energy is found to increase and saturate with
the number of LB layers. This result, unlike that expected for the iso
tropic van der Waals interaction, reveals the anomalous anisotropic in
terfacial tension between a liquid-crystal slab and polyimide LB films
with nanometer thickness. The generalized nonretarded van der Waals e
nergy for the chain-chain interaction is proposed to explain the exper
imental result.