Waveguide propagation of light in polymer porous films filled with nematic liquid crystals

We theoretically analyze the waveguide regime of light propagation in a cylindrical pore of a polymer matrix filled with liquid crystals assuming that the effective radial optical anisotropy is biaxial. From numerical analysis of the dispersion relations, the waveguide modes are found to be sensitive to the field-induced changes of the anisotropy. The electro-optic properties of the polymer porous polyethylene terephthalate (PET) films filled with the nematic liquid crystal 5CB are studied experimentally and the experimental results are compared with the results of the theoretical investigation.Comment: 15 pages, 10 figures, revtex4-

Effects of polarization azimuth in dynamics of electrically assisted light-induced gliding of nematic liquid-crystal easy axis

We experimentally study the reorientation dynamics of the nematic liquid crystal easy axis at photoaligned azo-dye films under the combined action of in-plane electric field and reorienting UV light linearly polarized at varying polarization azimuth, $\phi_p$. In contrast to the case where the light polarization vector is parallel to the initial easy axis and $\phi_p=0$, at $\phi_p\ne 0$, the pronounced purely photoinduced reorientation is observed outside the interelectrode gaps. In the regions between electrodes with non-zero electric field, it is found that the dynamics of reorientation slows down with $\phi_p$ and the sense of easy axis rotation is independent of the sign of $\phi_p$.Comment: revtex-4.1, 4 pages, 3 figure

Controlled Nanoparticle Targeting and Nanoparticle-Driven Nematic Structural Transition

We study experimentally and theoretically controlled targeting of specific nanoparticles (NPs) to different regions within nematic liquid crystal. Using a simple mesoscopic Landau-de Gennes-type model in terms of a tensor nematic order parameter, we demonstrate a general mechanism which could be exploited for controlled targeting of NPs within a spatially nonhomogeneous nematic texture. Furthermore, we experimentally demonstrate using polarising microscopy that even a relatively low concentration of localised appropriate NPs could trigger a nematic structural transition. A simple estimate is derived to account for the observed transition

Effect of combined action of electric field and light on gliding of the easy axis in nematic liquid crystals

A new effect is described of the combined action of an electric field and light on the slow surface dynamics in a layer of nematic liquid crystal (NLC) contacted with a layer of dye pre-treated by UV irradiation. Simultaneous application of a relatively weak ``in-plane'' electric field and polarised light resulted in slow variation of the boundary orientation of the sample transmitted to the bulk of the layer. At the same time, the separate action of the two factors mentioned above did not produce any visible changes in the LC layer at the same intensity and time of application. After turning off both the electric field and light, extremely slow relaxation of the system to the initial state was observed. This effect depends on a number of control parameters (applied voltage, intensity of light, time of application, dose of a preliminary UV irradiation). The critical slowing down of this process (up to some weeks) via a proper choice of control parameters was established. The physical processes responsible for the combined effect were considered and applied to modify a previously proposed phenomenological model for the electrically induced slow azimuthal rotation of the easy axis of an NLC. The modified model was found to be in a qualitative agreement with the main experimental results

Liquid crystals in electrically controlled hollow like fibers

The problem of liquid crystals application for an electrical control of light propagation in hollow like fibers is considered. It is shown that for radial electric field simple estimations of the threshold voltage can be made in terms of Freedericksz transition. The usage of weak surface anchoring was proposed as effective way to provide electrical control of orientation in surface layers of liquid crystals. It plays a key role for fiber optic applications

Liquid crystal in rectangular channels: New possibilities for three dimensional studies

The new construction of LC cell useful for a study both simple twist deformation and 3D structures in liquid crystals induced by boundaries and electric fields is proposed. One of the main advantages of the cell is a very high sensitivity of optical response to the small variations of the twist angle. It is possible to create homogeneous "in plane" electric field under special choice of dimensions of a rectangular channel filled with a liquid crystal. The new LC cell provides good perspectives for measurements of practically important viscous and elastic properties of liquid crystals including a rotational viscosity coefficient. The cell can be also used for. a study of static and dynamic properties of liquid crystals at weak anchoring