Energetics of topographically designed Smectic-A oily streaks.

A thin Smectic-A liquid crystal (LC) film is deposited on a polymer vinyl alcohol-coated substrate that had been scribed with a uniform easy axis pattern over a square of side length ≤ 85 μm. The small size of the patterned region facilitates material distribution to form either a hill (for a thin film) or divot (for a thick film) above the scribed square and having an oily streak (OS) texture. Optical profilometry measurements film thickness suggest that the OS structure aims to adopt a preferred thickness that depends on the nature of the molecule, the temperature, and the surface tension at the air interface.

Co-revolving topological defects in a nematic liquid crystal.

A patterned surface defect of strength = +1 and its associated disclination lines can decompose into a pair of surface defects and disclination lines of strength = +1/2. For a negative dielectric anisotropy liquid crystal subjected to an applied ac electric field , these half-integer defects are observed to wobble azimuthally for > than some threshold field and, for sufficiently large fields, to co-revolve antipodally around a central point approximately midway between the two defects. This behavior is elucidated experimentally as a function of applied field strength and frequency , where the threshold field for full co-revolution scales as .

Transition from escaped to decomposed nematic defects, and vice versa.

An escaped radial director profile in a nematic liquid crystal cell can be transformed into a pair of strength m = +1/2 surface defects (and their associated disclination lines) at a threshold electric field. Analogously, a half-integer defect pair can be transformed at a threshold electric field into a director profile that escapes into the third dimension. These transitions were demonstrated experimentally and numerically, and are discussed in terms of topologically discontinuous and continuous pathways that connect the two states.