Main-chain ordering and stability of the light-induced anisotropy in the films of comb-like azo-polymer

Yaroshchuk, O.; Tereshchenko, A. G.; Shans'ky, L. I.; Reshetnyak, Victor; Puchkovska, Galina A.; Lindau, J.

doi:10.1016/s0928-4931(99)00034-x

Cited by 11 publications

(23 citation statements)

References 9 publications

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“…According to Refs. [14,24], the latter factor seems to be of crucial importance in stabilizing the photoinduced order.…”

Section: Discussion and Conclu-sionsmentioning

confidence: 99%

“…In particular, it can be shown [31] that the results of Refs. [14,22,23,24,40] can be recovered by choosing suitably defined angular redistribution probabilities.…”

Section: Modelmentioning

confidence: 99%

“…In the past years this spatial character of the photoinduced anisotropies has not received much attention and, until recently, it has been neglected in the bulk of experimental and theoretical studies of POA in azobenzene containing polymers [4,12,13,14,19,20,21,22,23,24]. On the other hand, the problems related to the 3D orientational structures in polymeric films are currently of considerable importance in the development of new compensation films for liquid crystal (LC) displays [25] and the pretilt angle generation by the use of photoalignment method of LC orientation [26].…”

Section: Introductionmentioning

confidence: 99%

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Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

et al. 2003

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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 (angular redistribution of trans chromophores) or photoselection (angular selective trans-cis isomerization) mechanisms depending on the wavelength. At early stages of irradiation the films of both azopolymers are biaxial. This biaxiality disappears on reaching a state of photo-saturation. In the regime of photoselection the photo-saturated state of the film is optically isotropic. But, in the case of the photo-reorientation mechanism, anisotropy of this state is uniaxial with the optical axis dependent on the preferential alignment of azochromophores. 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.

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“…According to Refs. [14,24], the latter factor seems to be of crucial importance in stabilizing the photoinduced order.…”

Section: Discussion and Conclu-sionsmentioning

confidence: 99%

“…In particular, it can be shown [31] that the results of Refs. [14,22,23,24,40] can be recovered by choosing suitably defined angular redistribution probabilities.…”

Section: Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

et al. 2003

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“…This effect provides a means of having the lightcontrolled anisotropy and it makes the materials that exhibit POA very promising for use in many photonic applications [1,2]. Owing to extremely high efficiency of POA in side-chain polymers that contain covalently linked photochromic moieties such as azobenzene derivatives and are known as azopolymers, light induced ordering processes in these polymers have been the subject of intense experimental and theoretical studies in the last decade [2,3,4,5,6,7,8,9,10,11].…”

Section: Introductionmentioning

confidence: 99%

“…In addition to the long term stability of POA, this model accounts for biaxiality of the photoinduced orientational structures [4,17,18,19,20,21] that was neglected in the models of Refs. [7,8,10,11].…”

Section: Introductionmentioning

confidence: 99%

Kinetics of photoinduced anisotropy in azopolymers: models and mechanisms

Kiselev

2002

J. Phys.: Condens. Matter

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We consider the effect of photoinduced optical anisotropy (POA) in azopolymers. Using a unified approach to the kinetics of photo-reorientation we discuss the assumptions underlying the known theoretical models of POA and formulate a tractable phenomenological model in terms of angular redistribution probabilities and order parameter correlation functions. The model takes into account biaxiality effects and long term stability of POA in azopolymers. It predicts that under certain conditions two different mechanisms, photoorientation and photoselection, will dominate POA depending on the wavelength of pumping light. By using available experimental data, we employ the model to compute dependencies of principal absorption coefficients on the illumination time. Our calculations clearly indicate the different regimes of POA and the numerical results are found to be in good agreement with the experimental data.

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

Yaroshchuk

Kiselev

Zakrevskyy

et al. 2001

The European Physical Journal E

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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

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Main-chain ordering and stability of the light-induced anisotropy in the films of comb-like azo-polymer

Cited by 11 publications

References 9 publications

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

Kinetics of photoinduced anisotropy in azopolymers: models and mechanisms

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

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