Role of Monomer Alkyl Chain Length in Pretilt Angle Control of Polymer-Stabilized Liquid Crystal Alignment System

Abstract

The pretilt angle of liquid crystal (LC) molecules in LC cells was manipulated by adding a mixture of two photocurable monomers, alkyl acrylate and biphenyl diacrylate, into the LCs after the UV treatment. The hexyl acrylate and octadecyl acrylate were applied to examine the alkyl chain length effect on the pretilt angle control under the condition of a fixed concentration of biphenyl diacrylate. The LC alignment was continuously adjusted from homogeneous to homeotropic alignment in the polymer-stabilized LC system by simply increasing the alkyl acrylate concentration in the LCs. At a given molar concentration of alkyl acrylate, the addition of octadecyl acrylate exhibits higher pretilt angle than that of hexyl acrylate. Both the pretilt angle of the LCs and advancing contact angle of water on the inner surfaces of LC cells simultaneously changed due to surface chemical nature and surface roughness. The pretilt angle increases along with an increase in the advancing contact angle. As a consequence, the surface advancing contact angle acts as an index for pretilt angle control.

Surface grafted agents with various molecular lengths and photochemically active benzophenone moieties

“…These investigations revealed that the surface energy (contact angle of E7) was indeed varied by photo exposure. These results are promising also for liquid crystal related research because the pretilt angle 49 of the LC director (which is important for the electrooptic performance) on a surface depends on the (now photo controllable) contact angle. Moreover, n-BPS functionalized surfaces can potentially be applied straight-forwardly (for example by spin casting of high molecular weight solvents followed by photo exposure, for example through a photo mask) to fabricate surface coatings with controllable wetting properties.…”

Alignment Layer of Liquid Crystal Using Plant-Based Isoeugenol-Substituted Polystyrene

“…Based on the results of inducing LC alignment properties, we observed a general trend that polymers containing higher contents of the isoeugenol side group possessed a preference for vertical alignment of LC molecules. It has been known that the high tilt angles of LCs that produce vertical aligning properties are well correlated with low surface energy values on the alignment film and/or steric repulsion between LCs and the alignment surfaces [ 85 , 86 ]. For instance, polyimide derivatives having bulky and nonpolar groups such as 4- n -octyloxyphenyloxy and pentylcyclohexylbenzene exhibited vertical aligning behavior [ 53 ].…”

Tunable Liquid Crystal Alignment and Driving Mode on Lanthanum Aluminum Zirconium Zinc‐Oxide Thin Film Achieved by Convenient Brush‐Coating Method

“…[1][2][3][4] In addition, implementing various LC driving modes is important for achieving electrooptical (EO) performance according to the varying needs of customers; since the LC driving mode is controlled by the pretilt angle of the LC alignment layer, there have been many reported attempts to control it. [5][6][7][8] Accordingly, deposition of the film used as the alignment layer and an alignment treatment process to create characteristics that induce uniform LC alignment with diverse alignment states must be achieved.…”