On biaxiality of photoinduced structures in azopolymer films

Spatial orientational structures in the layers of liquid crystalline polymalonates are investigated using UV absorption method and the results of the null ellipsometry technique. Preferential in-plane alignment of azobenzene fragments and in-plane reorientation under irradiation with polarized UV light are established. The components of the order parameter tensor of azobenzene fragments are estimated for the initial state and after different doses of irradiation. The uniaxial as well as biaxial order of the azobenzene chromophores are detected. The biaxiality is observed in the intermediate stages of irradiation, whereas the uniaxial order is realized in the saturated state. The proposed theory takes into account biaxiality of the induced structures and describes well the experimental dependencies of the order parameter components on the time of irradiation.Шляхом використання методу УФ поглинання та результатів еліпсометричних вимірювань вивчені просторові орієнтаційні структури в шарах рідкокристалічних полімерів. Встановлено, що під дією поляризованого УФ випромінювання азобензольні фрагменти орієнтуються переважно в площині. Отримано оцінку для компонентів тензора параметра порядку як у початковому стані, так і після різних доз опромінювання. Виявлено як одновісне так і двовісне впорядкування азобензольних хромофорних груп. Причому двовісність спостерігається у проміжній стадії опромінювання, тоді як одновісний стан реалізується в режимі насичення. Запропонована теорія враховує двовісність індукованих структур і добре описує експериментальні залежності компонентів параметра порядку від часу опромінювання

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

Molecular structure of azopolymers and photoinduced 3D orientational order",

The combination of transmission null ellipsometry (TNE) and attenuated total reflection (ATR) methods supported by absorption measurements is shown to be an effective tool to study spontaneous and photoinduced 3D order in azopolymers. We investigated a series of azobenzene containing side-chain polyesters differing by the length of the main-chain spacer (CH 2 ) m (m ) 2, I. Introduction Presently, in the era of information technologies, there is an increasing interest in photonic processes allowing the improvement of devices for information storage, processing, displaying, and transfer. The phenomenon of photoinduced anisotropy (PIA) is one of the best candidates for this purpose. Photoinduced anisotropy (also named Weigert 1 effect) produces optical dichroism and birefringence in various materials by generating an orientational order. This order is centrosymmetric (quadrupolar) and should be more correctly named alignment, in contrast with the orientation induced by poling methods (photoassisted electrical poling (PAEP) 2 and all-optical poling (AOP) 3-5 ), which generate a noncentrosymmetric (dipolar and octupolar) orientational order, producing nonlinear effects ( (2) ). Azobenzene-containing polymers are known to be among the most effective materials for PIA generation. The microscopic explanation of PIA in azopolymers is based on two properties of azochromophores: 6,7,10 the trans-ci

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

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

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

Spatial reorientation of azobenzene side groups of a liquid crystalline polymer induced by linearly polarized light

The photoinduced 3D orientational structures in films of a liquid crystalline polyester, containing azobenzene side groups, are studied both experimentally and theoretically. By using the null ellipsometry and the UV/Vis absorption spectroscopy, the preferential in-plane alignment of the azobenzene fragments and in-plane reorientation under irradiation with linearly polarized UV light are established. The uniaxial and biaxial orientational order of the azobenzene chromophores are detected. The biaxiality is observed in the intermediate stages of irradiation, whereas the uniaxial structure is maintained in the photosaturated state of the photo-orientation process. The components of the order parameter tensor of the azobenzene fragments are estimated for the initial state and after different doses of irradiation. The proposed theory takes into account biaxiality of the induced structures. Numerical analysis of the master equations for the order parameter tensor is found to yield the results that are in good agreement with the experimental dependencies of the order parameter components on the illumination time

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