P‐83: Liquid Crystal Alignment on Substrates Treated with the Plasma Flux: Static and Dynamic Regimes of Irradiation

Abstract

In this paper, we present the new results related to LC alignment on the substrates obliquely treated with a “sheet” of accelerated Ar+ plasma generated by an anode layers thruster (ALT). The substrates of organic (polymers) and inorganic (glass, DLC, SiO2, etc.) origin were treated with the plasma flux in static and dynamic regime (unidirectional translation perpendicularly to plasma “sheet”). For LCs with Δ∍<0, in both regimes, 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 not equal to zero and can be varied with the incidence angle of plasma beam and the irradiation dose. The uniformity of pretilt angle is better in the dynamic regime. With the increase of irradiation dose, the alignment transition from the 1st to the 2nd mode occurs. For the LC mixtures with Δ∍<0, used for VA LCD, only the 1st mode alignment (uniform over the whole substrate) is realized. It occurs at low and even at the relatively high irradiation doses, which cause the 2nd mode alignment for the LCs with δ∍>0. The pretilt angle achieves values as high as 30° and can be controlled by the irradiation dose and by the incidence angle of plasma beam. The 2nd alignment mode is observed at high irradiation doses and only in the static regime of irradiation. It occurs in the central, most intensive part, of the plasma “sheet”, 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. The alignment transition 1st mode — two‐fold degenerate alignment — 2nd mode observed for LC with δ∍<0 is quite similar to the one earlier described for vapor deposition alignment. In the dynamic irradiation regime, for both types of LC, uniform alignment on the substrates as big as 15×15 cm is realized.

Plasma beam alignment for the large‐area substrates: Equipment and process

“…With an increase in the irradiation dose, the anchoring transition from the first to the second mode occurs through the transient two-fold degenerated alignment. 17 Together with the KSU group (Kent, OH, U.S.A.), 18 we revealed that aniso-tropy of the surface relief is a rather important factor for LC alignment and anchoring transition on the plasma-beamtreated substrates.…”

“…In the beginning, it is reasonable to determine whether the mode sequence, first mode -twofold degenerated alignment -second mode, realized with an increase in the exposure dose in a static irradiation regime, 17,18 is also observed in the translation regime of the irradiation. Figure 4 shows two sets of asymmetric cells in which the plasma-treated substrates (tested substrates) are processed over a different time in the second translation regime (Section 2.1).…”

Liquid Crystal Alignment on Plasma Beam Scanned Alkylsiloxane Self-Assembled Monolayers

“…Recently, Yaroshchuk et al reported that a sheetlike plasma source was able to modify the surface of a PI film for LC alignment. 14,15 The sheetlike plasma source was further modified into a plasma beam scanner, [16][17][18][19][20] where a plasma beam of elliptical shape was designed to scan across the alignment layer at a fixed angle of incidence. The plasma beam scanning technique was effective in improving the LC alignment on hydrogenated amorphous carbon ͑a-C:H͒ and PI alignment layers.…”