Under pulsed or a.c. electric fields, colloidal suspensions of nanorods can show strong electro-optic effects, such as the Kerr effect, with fast response times (a few ms), which makes them good candidates for some commercial applications. For this purpose, suspensions of Pigment red 176 nanorods in dodecane were recently developed and their physical properties have been studied. We report here on the investigation of the orientational order induced by electric fields in isotropic suspensions of pigment nanorods by three different techniques: transient electric birefringence, transient electric dichroism, and in-situ small-angle X-ray scattering under electric field ("Electro-SAXS"). We show that, in spite of the apolar character of the solvent, the Maxwell-Wagner-O'Konski mechanism (i.e. the polarization of the counter-ion cloud around each particle) is responsible for the field-induced alignment of the nanorods. Although the particles are only weakly charged and the dielectric constant of dodecane is low, the pigment nanorods effectively behave as metallic particles in an insulating matrix and reach strong values (S~0.5) of the induced nematic order parameter at moderate field amplitudes (~1 V/µm). This study confirms the feasibility of using suspensions of Pigment red 176 nanorods in dodecane for electro-optic applications.

In this report we consider behaviour of nematic LC on randomly aligning surface. We solved the theoretical problem on spatial distribution of director on a tested surface where easy axis lies in the azimuthal plane and is randomly distributed over the surface. We found that in combined cell angular distribution of director on the tested surface strongly depends on anchoring parameter and its dispersion. For strong anchoring the director distribution practically coincides with the easy axis distribution. Weaker anchoring results in narrowing of the admitted region of the director orientation, and emerging of maximum of the distribution function at the outermost angles of this region. The dispersion of anchoring energy over the surface leads to drastic transformations of the distribution function and shift of the maximum towards the smaller angles. We believe that results obtained will give us a powerful tool for studying LCaligning surface interfaces.

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We study the effect of an isotropic-nematic (I-N) phase transition on the liquid crystal alignment at untreated polymer surfaces. We demonstrate that the pattern at the untreated substrate in the planar cell where the other substrate is uniformly rubbed strongly depends on the temperature gradient across the cell during the I-N phase transition, being macroscopically isotropic if the untreated substrate is cooled faster, but becoming almost homogeneous along the rubbing direction in the opposite temperature gradient. We interpret the observed effect using complementary models of heat transfer and nematic elasticity. Based on the heat transfer model we show that the asymmetric temperature conditions in our experiments provide unidirectional propagation of the I-N interface during the phase transition and determine the initial director orientation pattern at the test's untreated surface. Using the Frank-Oseen model of nematic elasticity, we represent the three-dimensional director field in the nematic cell as a two-dimensional (2D) pattern at the untreated surface and perform 2D numeric simulations. The simulations explain the experimental results: Different initial director orientations at the untreated surface evolve into different stationary patterns.

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