Magnetic actuation of a thermodynamically stable colloid of ferromagnetic nanoparticles in a liquid crystal.

We report the development of a highly stable nanomaterial based on ferromagnetic nanoparticles dispersed in a thermotropic liquid crystal. The long-term colloidal stability and homogeneity were achieved through surface modification of the nanoparticles with a mixture of a dendritic oligomesogenic surfactant and hexylphosphonic acid and confirmed by optical and electron microscopy. The nanomaterial has an increased sensitivity to the magnetic field possessing collective and non-collective magneto-optical responses in contrast to the undoped LC.

Allergen extracts and recombinant proteins: comparison of efficiency of in vitro allergy diagnostics using multiplex assay on a biological microchip.

Background: Immunological test systems for diagnostics of type I hypersensitivity involve the following types of antigens: whole allergen extracts, individual highly purified proteins and their recombinant analogues. The goal of this study was to compare the results obtained with whole allergen extracts (birch pollen, cat dander, and timothy grass pollen) and their respective recombinant proteins in biochip-based immunoassay.

Methods: Multiplex fluorescent immunoassay of 139 patients' blood serum samples was carried out using biological microchips (biochips).

Electro- and photosensitive azopolymer for alignment of liquid crystals.

We report an electro- and photosensitive metal containing polymer material for alignment of liquid crystals (LCs). Irradiation with polarized light and/or application of dc-field result in an anisotropy of the polymer and formation of an easy orientation axes of a LC on the polymer surface. The light-induced anisotropy of the polymer and the LC anchoring on the polymer surface can be controlled by the low dc-field at room temperature.

Formation of liquid-crystal cholesteric pitch in the centimeter range.

The formation of a macroscopic cholesteric spiral in a nematic liquid crystal (LC) doped with chiral molecules is studied. Measurements of the orientation of the disclination line formed in a LC θ-cell manufactured with one substrate having linear in-plane alignment and the opposing substrate having circular alignment showed the formation of a uniform macroscopic cholesteric spiral with a pitch length of centimeters. We found a linear dependence of the reciprocal pitch p(-1) on the concentration c in a wide range of p, extending from micrometers up to several centimeters.

Recording of polarization holograms in a liquid crystal cell with a photosensitive chalcogenide orientation layer [Invited].

Polarization gratings have been recorded in a combined liquid crystal (LC) cell made of a substrate covered with a photosensitive chalcogenide orientation layer and a reference substrate covered with a rubbed polyimide film. The gratings are formed due to the spatially modulated light-induced easy orientation axis on the chalcogenide surface recorded by two beams with opposite circular polarizations. The gratings are permanent, but they can be erased by one of the recording beams and re-recorded.

Aging in glassy polymer-liquid-crystal layers.

We present in this Rapid Communication experimental evidence of an acceleration of the zenithal easy-axis dynamics of a nematic liquid crystal (NLC) with the age of a NLC-polymer layer. The comparison with other hard alignment layers strongly indicates that the polymer softness and its ability to reorient in the nematic ordering field is at the origin of the measured dynamics. The unusual acceleration of the dynamics with the polymer age is discussed in terms of this unique coupling with the NLC order.

Light-induced gliding of the easy orientation axis of a dye-doped nematic liquid crystal.

We studied the effect of light-induced gliding of the easy axis of dye-doped nematic liquid crystal on an aligning polymer surface. The observed drift of the easy axis is over tens of degrees and is caused by light-induced anisotropic adsorption and/or desorption of dye molecules on or from the aligning layer in the presence of light-induced bulk torque. We present a theoretical model that explains the experimental data in terms of the light-induced changes of the adsorbed dye molecules angular distribution due to their exchange with the dye molecules from the liquid crystal bulk.

Evolution of light-induced anchoring in dye-doped nematics: experiment and model.

A series of experiments was carried out to describe the evolution of light-induced anchoring in dye-doped nematic liquid crystals (LCs) at irradiation with polarized light. The experiments included cells filled with a pure pentyl-cyanobiphenyl (5CB) and containing a layer of azo dye deposited on an aligning film, as well as cells filled with azo dye doped 5CB, which allowed us to distinguish the role of "surface" and "bulk" dye molecules in the evolution of light-induced anchoring. Modifications of the spectra of spontaneously adsorbed dye molecules under illumination enabled us to assert that light-induced desorption is a mechanism responsible for producing an easy orientation axis in a dark-adsorbed layer.

Drag on particles in a nematic suspension by a moving nematic-isotropic interface.

We report a clear demonstration of drag on colloidal particles by a moving nematic-isotropic interface. The balance of forces explains our observation of periodic, striplike structures that are produced by the movement of these particles.