Photoinduced 3D orientational order in side chain liquid crystalline azopolymers

We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced 3D orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, correspondingly. Using irradiation with the polarized light of two different wavelengths we find that the kinetics of photoinduced anisotropy can be dominated by either photo-reorientation or photoselection mechanisms depending on the wavelength. We formulate the phenomenological model describing the kinetics of photoinduced anisotropy in terms of the isomer concentrations and the order parameter tensor. We present the numerical results for absorption coefficients that are found to be in good agreement with the experimental data. The model is also used to interpret the effect of changing the mechanism with the wavelength of the pumping light.Comment: uses revtex4 28 pages, 10 figure

Anisotropic surface morphology of azopolymer lms generated by polarized UV light irradiation

X-ray re ectivity measurements reveal anisotropy of the vertical surface roughness caused by exposure to linearly polarized UV (LPUV) light in the lms of two azopolymers. The irradiated surface is found to have higher roughness in the direction parallel to the direction of polarization than in the orthogonal direction. The photo-modi cation of the surface morphology is caused by spatial changes induced in polymer lms by LPUV irradiation. The important role of surface roughness anisotropy in determining the alignment of liquid crystals is discussed

A supramolecular approach to optically anisotropic materials: Photosensitive ionic self-assembly complexes

Application of the supramolecular-synthesis strategy ionic self-assembly for the facile production of low-molecular-weight photo-addressable materials (see figure) is presented. The materials have good film-forming properties, long-term thermal stability, and, most importantly, dichroic ratios of 50

La Spectroscopie de masse maldi tof appliquée à l'analyse de bactéries à gram positif (étude d'une série de 16 bactéries proches du genre Corynebacterium)

LYON1-BU Santé (693882101) / SudocSudocFranceF

Photoinduction of optical anisotropy in an azobenzene-containing ionic self-assembly liquid-crystalline material

Liquid-crystalline (LC) phase behavior and photoinduction of optical anisotropy in the ionic self-assembly complex 4-(4-diethylaminophenylazo) benzenesulfonate-dimethyldidodecylammonium (EO-C12D) has been investigated by polarized light microscopy, differential scanning calorimetry (DSC), x-ray scattering, null-ellipsometry, and UV-visible absorbance techniques. The complex exists in a bilayer smectic-A (smA(2)) LC phase at elevated temperatures (65-160 degrees C) and in a rectangular columnar (Col(r)) LC phase in the temperature range of -5-65 degrees C. Hysteresis in the transition from the smectic to the columnar LC phase was observed. Detailed experimental investigations of the phase behavior, film-forming properties, and induction of optical anisotropy were performed. High values of photoinduced anisotropy (dichroic ratio of approximately 50) were detected when thin films of the complex were irradiated with linearly polarized light (Ar+ laser, lambda=488 nm). It was shown that the azobenzene units align perpendicular to the polarization of the exciting light causing an alignment of the columns parallel to the light electric field vector. On the basis of all experimental results a model of the photoinduced alignment of the photochromic complex is proposed in which photoalignment of the material is connected to the reorientation of domains

Perylenediimide-surfactant complexes: thermotropic liquid-crystalline materials via ionic self-assembly

In this communication we present the facile preparation and characterisation of thermotropic liquid-crystalline materials from the ionic self-assembly of a charged perylenediimide derivative and oppositely charged surfactants

Highly ordered monodomain ionic self-assembled liquid-crystalline materials

Liquid-crystalline properties of the ionic self assembled complex benzenehexacarboxylic-(didodecyltrimethylammonium)(6)[BHC-(C12D)(6)] were investigated by polarizing microscopy, differential scanning calorimetry (DSC), x-ray analysis, null ellipsometry, UV and IR spectroscopy. The complex exhibits a bilayer smectic Sm-A(2) liquid-crystalline phase and aligns spontaneously. Alignment properties do not depend on the hydrophobic or hydrophilic treatment of the surfaces. The aligned complex possesses a negative (Delta n=-0.02) homeotropically oriented optical axis, with layers aligned parallel to the surface. X-ray analysis of the aligned sample revealed a lamellar structure with a d spacing of 3.15 nm, consisting of sublayers of thicknesses d(1)=1.41 and d(2)=1.74 nm. This was confirmed by simple geometrical calculations and detailed temperature-dependent investigations, revealing that the first layer contains the BHC molecules and oppositely charged groups of the surfactants, and the second the alkyl tails of the surfactant. Changes in the order parameters (as calculated from the IR investigations) are correlated with the phase transitions as found by DSC. The properties of the complex are strongly influenced by the ionic interactions within the complex. The presence of these groups slows down the dynamics within the material sufficiently to allow for crystallization of the complex from an aligned LC phase into a single crystal domain, as well as restricting the transition to the isotropic phase