Alignment layer

Homeotropic anchoring can be achieved using monolayer smfactants such as lecithin and silane. The polar head of the surfactant is chemically attached to the glass substrate, and the hydrocarbon tail points out and perpendicular to the surface, as shown in Figme 1.19(b). 

The intermolecular interaction between the surfactant and the liquid crystal promotes the 

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D Sainova, A Zen, HG Nothofer, U Asawapirom, U Scherf, R Hagen, T Bieringer, S Kostromine, and D Neher, Photoaddressable alignment layers for fluorescent polymers in polarized electroluminescence devices, Adv. Fund. Mater., 12 49-57, 2002. 

Fig. 4.17 Model of a carbon nanoshell pointing to the stacks of 5-10 aligned layers within the shell. Hydrogen can possibly bond to the dangling bonds on the periphery of layered graphitic...

As indicated above, much interest exists in dynamic behavior of thin aligned layers of nematic liquid crystals. It is not surprising to find, therefore, that measurement of the anisotropy of transport properties has been the objective of many studies of thermotropic systems. The literature on anisotropic thermal conductivity in nematic liquid crystals has been reviewed recently by Rajan and Picot (12). Among the studies of anisotropic diffusion are those of Yun and Fredrickson (13), Bline... 

Tuning of the pre-tilt angle at the interface was also demonstrated by doping commonly used polyimide alignment layers with POSS nanoparticles [339]. In addition, the fabrication of a tunable liquid crystal flat microlens was achieved by placing a drop of a nematic liquid crystal doped with POSS nanoparticles onto a substrate inducing planar alignment (local HAN mode) [340]. Simultaneously, Takatoh and co-workers extended this concept to a series of metal oxide... 

Electro-optic effects induced by doping liquid crystals with one-dimensional metal nanoparticles were not only investigated in standard electro-optic test cells, but also in costume-made cells consisting of a thin layer of liquid crystal either deposited onto a thin film of alumina with embedded GNRs [443], or using rubbed polyimide alignment layers modified with solution-cast GNR [444]. In both cases, surface plasmon resonance frequencies of the GNR integrated into these liquid crystal cells could be electrically controlled. 

Relatively few reports exist at this time describing media that are both switchable and erasable. The general strategy has been to record the information in the form of a reversible surface effect, either on an alignment layer or on the inner surfaces of a PDLC. In this situation, the control of alignment of an LC can be switched between surface and electric field effects, such that the on state alignment is provided by the surface control and the off state alignment is provided by the electric field. 

Fig. 17 T-V profile for 5CB with the photosensitive PI as an alignment layer, and optical switching behavior.

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