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

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, De, 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 De > 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 De < 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, whileThese studies are partially supported by INTAS 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 AE45 with respect to the alignment direction in the 1st mode area. This sequence of the alignment transitions is observed in both LC with De > 0 and De < 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.

Role of Surface Anchoring and Geometric Confinement on Focal Conic Textures in Smectic-A Liquid Crystals

“…At surfaces, liquid crystal molecules anchor in a particular orientation due to intermolecular interactions with the substrate molecules. Common configurations are ‘planar' in which molecules align parallel to the substrate and ‘homeotropic' in which molecules align perpendicular to the substrate. , These conditions can be controlled by adsorbing hydrophilic or hydrophobic molecules onto the substrate or by rubbing to create fine grooves in the surface, among other methods. − In the present work, a planar anchoring condition on PDMS film is established by oxidizing the PDMS surface in air plasma. , We also show that the hydrophobic PDMS surface with no special treatment imposes a homeotropic anchoring condition, consistent with observations reported elsewhere. , …”

Liquid Crystal Alignment on Hydrogenated Amorphous Carbon Films Scanned by Divergent Ar Plasma Beams

“…4) In recent years, many non-contact methods have been developed such as photo-alignment, 5) ion beam alignment, [6][7][8][9] and plasma beam alignment. [10][11][12][13][14][15] Yaroshchuk et al illustrated the sheet-like plasma fluxes extracted from the anode layer source could modify the surfaces of PI and hydrogenated amorphous carbon (a-C:H) films in favor of LC alignment. [10][11][12][13] Recently, a plasma beam scanner was developed based on the concept of sheet-like plasma fluxes to enhance the LC alignment for a-C:H films, in which an elliptical plasma beam was designed to scan across the substrate at a fixed angle of incidence.…”

“…[10][11][12][13][14][15] Yaroshchuk et al illustrated the sheet-like plasma fluxes extracted from the anode layer source could modify the surfaces of PI and hydrogenated amorphous carbon (a-C:H) films in favor of LC alignment. [10][11][12][13] Recently, a plasma beam scanner was developed based on the concept of sheet-like plasma fluxes to enhance the LC alignment for a-C:H films, in which an elliptical plasma beam was designed to scan across the substrate at a fixed angle of incidence. In our previous work, the LC alignment occurred for the as-scanned a-C:H film, which has been attributed to the reformation of C-O bonds on the asscanned a-C:H film after exposure to air.…”