Electro-optical effect dispersion

Dispersions of nanoparticles in ferroelectric liquid crystals (FLCs) predominantly focused on induced or altered electro-optic effects, but also on the alignment of FLCs. Raina and co-workers reported on a gradual decrease of the dielectric permittivity, e, by doping with SiC>2 nanoparticles at frequencies up to 1 kHz and a rather minor increase of as well as an increase in optical transmission at frequencies above 2 kHz [279]. Liang et al. used BaTiC>3 nanoparticles (31 nm in diameter after grinding commercially available 90 nm nanoparticles Aldrich) and showed, perhaps expectably, a twofold increase in the spontaneous polarization... 

It has been established experimentally that the origin of the electro-optic effect in organic materials is largely electronic. This implies that the linear electro-optic coefficient can be estimated from the second harmonic coefficient. By properly accounting for the dispersion (using a two level model), the electronic contribution to the electro-optic coefficient is calculated to be r5 3 - 2.4 0.6 x 10 m/V at X-O.S m. Measured values of the electro-optic coefficient are in agreement within experimental uncertainty. These values compare favorably with that of GaAs (r4i - 1.2 x 10 m/V). 

B. High-Frequency Dispersion of the Electro-Optical Effect... 

H. S. Kitzerov, H. Molsen, and G. Heppke, Linear electro-optic effects in polymer-dispersed ferroelectric liquid crystals. Apll. Phys. Lett. 60, 3093-3095,1992. 

The electro-optic effect was also studied in polymer dispersed liquid crystal (PDLC) films [86]. With respect to nonchiral nematic PDLC films, the transmission is lower, but the angular dependence is improved. 

Electro-optical devices based on the same principles of the GDLCs in which the host matrix for the LC is made by bacterial activity (biofilm) [16] have been reported. In order to exhibit the electro-optical effect, liquid crystal dispersion devices require a specific structure in terms of macroporosity and refractive index of the matrix. Efficient light scattering (in the off-state) is obtained only when the LC forms microdomains in the porosity of the embedding matrix moreover, the refractive index of the matrix must be similar to that of the... 

Karapinar R, Neill MO, Hird M (2002) Polymer dispersed ferroelectric liquid crystal films with high electro-optic quality. J Phys D Appl Phys 35(9) 900-903 Kitzerow HS, Molsen H, Heppke G (1992) Linear electro-optic effects in polymer-dispersed ferroelectric liquid crystals. Appl Phys Lett 60 3093 Kossyrev PA, Qi J, Priezjev NV, Pelcovits RA, Crawford GP (2002) Virtual surface, director domain and the Freedericksz transition in polymer-stabilized liquid crystals. Appl Phys Lett 81 2986... 

Most reports over the past 4 years have dealt with the manipulation of display-related parameters such as electro-optic response and alignment, but increasingly also with thermal effects, pattern formation, nanoparticle-liquid crystal compatibility (i.e., enhancing the stability of dispersions), and to some degree with nanoparticle organization. 

Yoshida et al. recently disclosed an alternative method that allowed them to produce stable suspensions of gold nanoparticles (1-2 nm in diameter) in nematic liquid crystals [315]. They used a simple sputter deposition process, which allowed them to prepare thin liquid crystal films of well-dispersed gold nanoparticles in both 5CB and E47 (available from Merck) with a nanoparticle size depending on the used nematic liquid crystal. Unfortunately, the authors did not provide any details on whether the nanoparticles were capped with a ligand or bare, non-coated particles, which makes it difficult to assess and compare the reported thermal as well as electro-optic data. However, very similar effects were found as a result of nanoparticle doping, including lower nematic-to-isotropic phase transition temperatures compared to the used pure nematics as well as 10% lower threshold voltages at nanoparticle concentrations below 1 wt% [315]. 

Kaino and co-workers [255] have investigated the effect of polymer polydis-persity on electro-optic materials properties. No dependence on polydispersity was observed for guest host materials but for Disperse Red chromophores covalently attached to monodisperse polystyrene weaker absorption tails were observed. This result suggests that chromophore-chromophore interactions are modified by the polymer host. 

The experimental value of r, , also agrees fairly well with the predicted value of 48 pm that was calculated from by using a two-level model suggested by Katz and Singer et al. [33], after accounting for dispersion effects from both the EFISH and electro-optic measurements. The r, , is expressed as ... 

For the electro-optical Pockels effect (EOPE), the dispersion simplifies to... 

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