Light-addressable liquid crystal polymer dispersed liquid crystal

Scattering-free liquid crystal polymer-dispersed liquid crystal polymer (LCPDLC) films are fabricated by combining a room temperature polymerizable liquid crystal (LC) monomer with a mesogenic photosensitive LC. The morphological and photosensitive properties of the system are analysed with polarized optical microscopy and high resolution scanning and transmission electron microscopy. A two-phase morphology comprised of oriented fibril-like polymeric structures interwoven with nanoscale domains of phase separated LC exists. The nanoscale of the structures enables an absence of scattering which allows imaging through the LCPDLC sample without optical distortion. The use of a mesogenic monomer enables much smaller phase separated domains as compared to nonmesogenic systems. All-optical experiments show that the transmitted intensity, measured through parallel polarizers, can be modulated by the low power density radiation (31 mW/cm2) of a suitable wavelength (532 nm). The reversible and repeatable transmission change is due to the photoinduced trans-cis photoisomerization process. The birefringence variation (0.01) obtained by optically pumping the LCPDLC films allow their use as an alloptical phase modulato

Enhanced magneto-optical properties of suspensions of spindle type mono-dispersed hematite nano-particles in liquid crystal

We explored how to increase liquid crystal sensitivity to external magnetic fields. Suspensions consisting of a mixture of liquid crystal and spindle type mono-dispersed hematite nano-particles at concentrations lower than 1 wt% were prepared. The Freacuteedericksz transition threshold for the suspensions appeared to be lower than for the pure liquid crystal. It was proved that adding canted antiferromagnetic nano-particles in liquid crystals increased their sensitivity to magnetic field while no change of the basic mesogenic properties of the matrix occurred

Laser Beam Modulation Freezing on a Liquid Crystal Surface

We report the first observation of the formation of permanent light-induced annular patterns in a planar cell filled with dye-doped liquid crystal. The sample is placed between one rubbed surface, giving unidirectional planar alignment, and one isotropic surface, providing degenerated planar alignment. The patterns appear under the irradiation of the isotropic surface through the liquid crystal layer. The experimental results are explained in terms of spatial modulation of the light polarization over the isotropic surface, due to conformation nonlinearity of the mixture. The light-induced adsorption of azo-dye on the initially isotropic surface leads to "freezing" of this modulation and the appearance of a twisted director structure

Properties of bulk-mediated photoalignment of doped liquid crystal

We have found that producing a light-induced easy axis in a liquid crystal cell doped with methyl red can result in surface director reorientation both toward and outward the polarization of the incident light. This pointed out two different mechanisms of light-induced anchoring in the system. We proposed that these mechanisms are light-induced anisotropy in the adsorbed MR-layer and light-induced adsorption of MR molecules on the substrate. The study of light-induced anchoring in the isotropic phase showed that the mechanism of light-induced anisotropy in adsorbed MR-layer prevails at small light intensities, whereas the mechanisms of light-induced adsorption dominates at high intensities