The Multimode LC Alignment on the Substrates Obliquely Treated with a Plasma Flux

Abstract

ABSTRACT We describe a variety of liquid crystal (LC) alignment modes on the aligning substrates obliquely treated with a flux of accelerated plasma from the anode layer thruster (ALT). The discharge area has a form of race track so that the generated flux contained two sheets of plasma corresponding to linear parts of the discharge. Within each “sheet” the intensity of flow (ion current density) is uniform in the direction parallel to the linear part of discharge. Across the “sheet”, the intensity of flow has the Gaussian distribution. The alignment of LC with positive and negative dielectric anisotropy, Δϵ, was tested on the substrates of organic (polymers) and inorganic (glass and DLC) origin treated in static and dynamic regime (unidirectional translation perpendicularly to plasma “sheet”). In the dynamic regime of irradiation, with the substrate moving with respect to the plasma beam, for LC with Δϵ > 0 we observed two aligning modes, with the easy axis confined to the plane of plasma incidence (mode 1) or perpendicular to this plane (mode 2). In the 1st aligning mode the LC pretilt angle is non-zero and can be varied with the incidence angle of plasma beam and the irradiation dose. With the increase of irradiation dose, the alignment transition from the 1st to the 2nd mode occurs. For LC with Δϵ < 0 only the 1st alignment mode uniform over all substrate was observed. In the static regime of irradiation, characterized by smooth distribution of the particle's flow across the sheet, two modes are clearly observed simultaneously; 2nd mode alignment occurs in central, most intensive part of flow, while the periphery part shows the 1st mode. The areas of the 1st and the 2nd mode are separated with the narrow transition area showing multidomain (two-fold degenerate) LC alignment. The easy axis in these domains is turned by about ±45° with respect to the alignment direction in the 1st mode area. This sequence of the alignment transitions is observed in both LC with Δϵ > 0 and Δϵ < 0. We also describe a high-tilt alignment (87°–90°) in the 1st mode realized on the hydrophobic polymers at the extremely low doses of plasma irradiation. The origin of the observed alignment effects is discussed.