LC alignment

Switching of an H-PDLC has also been accomplished mechanically [29], By using a relatively elastic photopolymer, De Rosa and coworkers were able to switch off the gratings by applying a shear stress to the cell. LC alignment may play a role in the results, however, the authors attributed the effect to a tilting of the grating. In other words, the direction of diffraction should be reversibly tunable by this method. 

Figure 7 Recording geometry for beam coupling through the photorefractive effect. The LC alignment, enforced by either surface or field effects, is usually homeotropic.

Photochemical Control of LC Alignment by Linearly Polarized Light... 

Manipulation of LC Alignment through Photoactive Surface Layers I 381... 

The ability to align LC elastomers with mechanical forces means that applications where LC alignment is necessary may be accessible through... 

A striking observation when studying LCs alignment between two glass plates is that it seems that an LC layer is stuck to the glass and remains there whatever the movement of the glass plates relative to one another or even if the LC is converted to its... 

Fig. la,b demonstrates the top view of the as-anodized porous alumina and the LC alignment on this surface. The LC alignment on the porous alumina film was the same as on the planar non anodized area of the aluminum film (the top left part in Fig. lb). It means that the LC could not penetrate in the pore space through the narrow pore entrance. The porosity of as-anodized films was about 15 %, and pore had the bottleneck form with the entrance diameter of about 5-10nm[6]. Such narrow pore entrance was not enough for the LC penetration into the closed porous space resulting in its horizontal alignment on the porous surface as on the planar non anodized aluminum surface. 

Pore etching allows to rich the porosity up to 60 % and the pore entrances up to 20-30 nm (Fig. lc). In this case the LC alignment has vertical orientation as shown in Fig. Id. The top left part in Fig. Id is planar non anodized area of the initial aluminum film with the horizontal LC alignment. It should be noted that LC penetration in the alumina porous structure with 60 % porosity was almost complete. 

Figure 1. Porous alumina surface and a LC alignment into the porous alumina with different postanodizing treatments a) the as-anodized (Uf=20 V) porous alumina surface b) the LC on the as-anodized porous alumina c) the porous alumina surface after the pore enlargement for 30 min d) the LC on the porous alumina after pore etching.

Classification of LC alignment into planar or homeotropic is an oversimplification. Under suitable conditions, the nematic director may make an angle with the substrate surface (Fig. 24). The observations between crossed polarizers of such samples are the... 

Figure 8.12. UV-visible spectra after cross-linking (upper) and LC alignment behavior as the command surface. Upon UV irradiation, LC is aligned in parallel with the SRG structure. Reprinted with permission from the American Chemical Society.

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