Photoalignment characteristics

The liquid crystalline characteristics of cinnamate esters have been examined and novel azo bearing systems have been made based on 4-[N-ethyl-N-(2-methacryloyloxyethyl)]amino-4 -(2-cinnamoyloxyethylcarbonyl)-2 -(nitroazoben-zene). Poly[4-(2-methacryloylethoxy)azobenzene] has been found to be valuable for the photocontrol of liquid crystalline alignment as have polymers with benzylidene phthalimidine side chains. Poly(methyl methacrylates) with o-cinnamate side chains undergo polarisation isomerisation resulting in photoalign-... 

Degradation of the polymer by deep U V exposure is a concern when photoalignment is used for the alignment process of LCD manufacturing. The generation of many radicals was confirmed by ESR measurements after UVexposure [26]. Do these radicals affect the display characteristics of the LCD panels Here, we will describe our study of the effects of UVexposiu-e on the characteristics of the LCD [25]. 

Unfortunately, the parameter t cannot be exactly calculated due to the complicated nature of the numbered interactions and molecular kinetics, but r should be much smaller than the time of light exposure to enable the azo-dye molecules to get to a new orientational state. Parameter t can be estimated from experiments on photoaligning. If kT 10 ° J (room temperature), a 10 cm", I 10" W/cm, Vm 10" ° cm, then x 10 to 10" s for A 0.1 to 1. The latter limits of the parameter values have been found from experimental data [10, 18]. We assume that the characteristic molecular size is about 20-30 angstroms (Figure 2.4) and estimate the absorption coefficient from the measured optical density D D 0.2 for an azo-dye layer thickness of 10 nm) [10]. The values of the coefficient A 0.1 - 1 provide the best fitting of the experimental curves by the diffusion model (see the results below). The time x may be dependent on the thermal conductivity of substance k, heat capacity Cp, density p, and characteristic size of sample L on which the distribution of temperature becomes homogeneous, i.e. r L Cpp/K. Since p 1 g/cm, Cp 1.6 J/g/K, ic 0.1 W/m/K, we obtain the estimate x 10"" s for L 2 jxm [18]. 

Comparison of the Characteristics of Photoalignment Layers for Different Mechanisms of LC Photoalignment... 

Table 3.1 Characteristics of photoalignment layers for various mechanisms of LC photoalignment (Chapter 2)...

D.-S. Seo and J.-M. Han, Generation of pretilt angle in NLCs and EO characteristics of a photoaligned TN-LCD with oblique non-polarized UV light irradiation on polyimide surface. Liquid Crystals 26, 959 (1999). 

J.-Y. Hwang, D.-S. Seo, J.-Y. Kim, and T.-H. Kim, Electro-optical characteristics in the photoaligned vertical-alignment cell on a photopolymer surfaces containing N-(phenyl)maleimide. Japanese Journal of Applied Physics 41, L58 (2002). 

The estimated values of the azimuthal and polar anchoring energy of the photoaligned LC layer were 4 x 10 " J/w and 5 x 10 J/m respectively, which are almost comparable with that of the rubbed polyimide layer. Consequently, photoaligned LCOS panels have the same electro-optical characteristics as the usual ones prepared by rubbing (Figure 6.6). 

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