The effect of substrate topology on smectic liquid crystal alignment: A high-resolution x-ray diffraction study

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:7236322

Smela, E

Surface topography is theoretically predicted to affect liquid crystal alignment through mechanical interactions: elastic deformations of the director are energetically unfavorable, causing the molecules to realign to minimize the distortion energy. Octylcyanobiphenyl (8CB), a bilayer smecticA liquid crystal at room temperature, was deposited on gratings, grids, and flat surfaces, and was studied using high resolution x-ray diffraction at shallow angles of incidence. One surface of the film was in contact with air and the other was in contact with a treated glass or silicon substrate. At the air interface, surface tension forces caused the liquid crystal molecules to align perpendicularly with respect to the plane of the substrate. Competing with the LC-air interface, which is a strong aligner, a grating at the LC-substrate interface produced distortions in the smectic layering which resulted in excess elastic energy and favored alignment parallel to the substrate and the grooves. The results show that in films less than approximately 30 [mu]m thick, the homeotropic orientation was maintained throughout the film due to the constraint of perpendicular alignment at the air interface. However, for thicker films on gratings, Bragg scattering from molecules lying parallel to the grooves was observed. The free air surface was thus the strongest aligning force, followed by the surface topology, while surface anchoring was not found to play a role.

• Research Organization: Pennsylvania Univ., Philadelphia, PA (United States)
• OSTI ID: 7236322
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
LIQUID CRYSTALS
ALIGNMENT
DEPOSITION
X-RAY DIFFRACTION
SUBSTRATES
SURFACE PROPERTIES
TOPOLOGY
CRYSTAL STRUCTURE
ORDER-DISORDER TRANSFORMATIONS
COHERENT SCATTERING
CRYSTALS
DIFFRACTION
FLUIDS
LIQUIDS
MATHEMATICS
PHASE TRANSFORMATIONS
SCATTERING
360602* - Other Materials- Structure & Phase Studies