Effects of polarization azimuth in dynamics of electrically assisted light-induced gliding of nematic liquid-crystal easy axis

Dubtsov, Alexander V.; Shmeliova, Dina V.; Pasechnik, S. V.; Kiselev, Alexei D.; Chigrinov, Vladimir G.

doi:10.1063/1.3701781

Cited by 9 publications

(15 citation statements)

References 20 publications

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“…9(a)-(c)). Similar to previously reported results, [4][5][6] separate action of light irradiation at appropriate parameters did not induce changes in easy axis position. Figure 9(b) and (c) presents microscopic images of a spot in crossed (b) and parallel (c) polarizers after the LPUV irradiation assisted by permanent magnetic field.…”

Section: Regime B: Light-induced Reorientation Of Nlc Assisted By "Insupporting

confidence: 92%

Electric and magnetic fields in photoalignment of liquid crystals

et al. 2015

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-The results of investigation of slow surface dynamics (easy axis gliding), induced by secondary illumination of photoaligned substrates with linearly polarized UV or blue light in the presence of electric (magnetic) fields, are presented for the first time. The initial surface orientation of nematic liquid crystal (NLC) was provided, in accordance with the standard photoalignment technique, via preliminary UV treatment of the glass substrates coated by sulfonic azo-dye SD1 film. The experiments fulfilled for the two geometries, A and B, corresponding to the normal (A) and parallel (B) orientation of fields relatively to liquid crystal (LC) layer, revealed different effects induced by electric (magnetic) fields. For geometry A, strong electric field applied, in combination with a linearly polarized blue light, to the planar layer in a sandwich-like LC cell with two photoaligned substrates results in simultaneous reorientation of easy axis on both substrates. It demonstrates the possibility of an azimuthal rotation of monodomain planar samples of LCs. For geometry B, usage of "in-plane" electric (magnetic) fields in the cell, composed of photoaligned and rubbed substrates, speeds up reorientation process of NLC easy axis respectively to pure light-induced reorientation. It provides electric control of operating times in previously proposed optical rewritable technology.

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Section: Regime B: Light-induced Reorientation Of Nlc Assisted By "Insupporting

confidence: 92%

Electric and magnetic fields in photoalignment of liquid crystals

et al. 2015

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“…For azo-dye films, the experimental data of Refs. [42,69] also suggest the presence of a threshold when the polarization vector E U V is directed along the initial easy axis (see the subsequent section for more details). Our result that under certain conditions highly ordered initial distributions may relax to the metastable stationary state offers a possible explanation for this.…”

Section: Computational Procedures and Bistability Effectsmentioning

confidence: 94%

“…In Sec. IV we apply the model to interpret the experimental data on the light-induced azimuthal gliding of the easy axis on the photoaligned SD1 substrate measured as part of the investigation into effects of the polarization azimuth in the dynamics of the electrically assisted light-induced gliding [42]. Finally, in Sec.…”

Section: Introductionmentioning

confidence: 95%

Photoinduced reordering in thin azo-dye films and light-induced reorientation dynamics of the nematic liquid-crystal easy axis

et al. 2012

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We theoretically study the kinetics of photoinduced reordering triggered by linearly polarized (LP) reorienting light in thin azo-dye films that were initially illuminated with LP ultraviolet pumping beam. The process of reordering is treated as a rotational diffusion of molecules in the light intensity-dependent mean-field potential. The two-dimensional diffusion model which is based on the free energy rotational Fokker-Planck equation and describes the regime of in-plane reorientation is generalized to analyze the dynamics of the azo-dye order parameter tensor at varying polarization azimuth of the reorienting light. It is found that, in the photosteady state, the intensity of LP reorienting light determines the scalar order parameter (the largest eigenvalue of the order parameter tensor), whereas the steady state orientation of the corresponding eigenvector (the in-plane principal axis) depends solely on the polarization azimuth. We show that, under certain conditions, reorientation takes place only if the reorienting light intensity exceeds its critical value. Such threshold behavior is predicted to occur in the bistability region provided that the initial principal axis lies in the polarization plane of reorienting light. The model is used to interpret the experimental data on the light-induced azimuthal gliding of the liquid-crystal easy axis on photoaligned azo-dye substrates.

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“…It results in slow change of preferable overall orientation (an easy axis) of LC molecules absorbed by surface. Such so-called gliding of an easy axis depends on a number parameters like a preliminary and a secondary doses of irradiation, the initial angle (an azimuth φ L ) of a polarization plane of the secondary irradiation respectively to that at preliminary irradiation, electric field strength for a case of a combined action of light and field [25,26]. It demands some time (ranging from some seconds to some hours) to reach new stationary direction of surface and bulk orientation, corresponding to the rotation of the sample by the angle φ ≈ φ L .…”

Section: Experimental Results Of Viscosity Measurementsmentioning

confidence: 99%

Photo Controlled Surfaces in Rheology of Liquid Crystals

Pasechnik

Semina

Shmeliova

et al. 2015

Molecular Crystals and Liquid Crystals

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The modified method for shear viscosity measurements of nematic liquid crystals (NLC) oriented by surfaces is described. The main modification is concerned with usage of photoalignment technique for preparation of mono-domain samples with an orientation controlled by a polarization state of the secondary light irradiation. It provides the azimuthal rotation of a sample at any desirable angle. Thus different geometries of shear flows can be realized after filling the measuring cell with a liquid crystal. The method is experimentally approved at investigation of Poiseuille decay flows of 4-pentyl-4-cyanobiphenyl (5CB) through the channels with a rectangular cross section. The proposed construction of the cell with different surface treatment provides measurements of the three principal viscosities coefficients (Miesowicz' viscosities) with additional usage of electric field. A small amount (less than 0.2 ml) of a liquid crystal needed for measurements and simple measuring procedure makes the method to be useful for rheological studies of newly synthesised liquid crystal materials.

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Effects of polarization azimuth in dynamics of electrically assisted light-induced gliding of nematic liquid-crystal easy axis

Cited by 9 publications

References 20 publications

Electric and magnetic fields in photoalignment of liquid crystals

Electric and magnetic fields in photoalignment of liquid crystals

Photoinduced reordering in thin azo-dye films and light-induced reorientation dynamics of the nematic liquid-crystal easy axis

Photo Controlled Surfaces in Rheology of Liquid Crystals

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