Probing a Local Viscosity Change at the Nematic-Isotropic Liquid Crystal Phase Transition by a Ratiometric Flapping Fluorophore

Local viscosity change in the thermal phase transition of a nematic liquid crystal, 5CB, has been analyzed by doping fluorescent viscosity probes, flapping fluorophores (FLAP) as well as a molecular rotor BODIPY-C12. As a result, only flapping anthraceneimide has successfully monitored a small viscosity change (corresponding to a few cP (centipoise) change in shear viscosity around 25 cP) in the nematic-to-isotropic phase transition by ratiometric spectroscopy. In addition, analysis of fluorescence anisotropy indicates that the emissive species (planarized flapping anthraceneimides) are aligned parallel to the director of 5CB in the nematic phase.

Higly sensitive active medium of sensor NO2 , based on cholesteric nematic mixture with impurities of carbon nanotubes

The paper presents the results of the study of the parameters of the highly sensitive active medium of the NO2 sensor based on a cholesterol-nematic mixture with an admixture of carbon nanotubes. The dependence of the change in the wavelength of the two transmission minima on the NO2 concentration for cholesterol-nematic mixture with single-walled, double-walled and multi-walled nanotubes at different concentrations of nanotubes and two concentrations of nematically liquid crystal 5CB were obtained. It is established that by changing the ratio between the concentrations of nanotubes and nematic liquid crystals, it is possible to obtain mixtures that have the maximum spectral sensitivity coefficient in a given range of gas concentration.

Effect of nature and degree of crosslinking agent of poly(hydroxy-butyl-methacrylate-co-2-ethyl-hexyl-acrylate) networks on the swelling properties in nematic liquid crystal 5CB

We experimentally measured the effect of nature and concentration of crosslinker on the photopolymerized time of the poly(hydroxy-butyl-methacrylate-co-2-ethyl-hexyl-acrylate)/5CB system. Initial mixtures are composed of monofunctional monomers hydroxy-butyl-methacrylate (HBMA) and 2-ethyl-hexyl-acrylate (2-EHA), and one of the three bifunctional monomers, poly-propylene-glycol-di-acrylate (PPGDA), tri-propylene-glycol-di-acrylate (TPGDA), or 1,6-hexane-diol-di-acrylate (HDDA), and 2-hydroxy-2-methylpropiophenone (Darocur 1173) as a photoinitiator. The copolymers were elaborated via UV irradiation of reactive formulation. The central composite face-centered design of experiments (DoE) has been used to determine the influence of temperature, crosslinking density and their interactions on swelling behavior of poly(HBMA-co-EHA/crosslinker) networks in liquid crystal 5CB. The experimental results and the predicted responses indicate a good correlation and therefore the validity of the used model.

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 electrooptic 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.