Laser-induced surface and bulk reorientation of the director in azo-dye-doped liquid crystal cells

Serak, Svetlana V.; Kovalev, A. A.; Agashkov, A. V.; Gleeson, H. F.; Watson, Sandra; Reshetnyak, Victor; Yaroshchuk, O.

doi:10.1016/s0030-4018(00)01111-1

Cited by 11 publications

(9 citation statements)

References 24 publications

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“…The BL131/130 mixture has an extremely broad chiral nematic phase with no close underlying smectic A (SmA) phase. It has been shown previously that the pitch increases slightly with increasing temperature [12]. The mixture TM1001 exhibits a room temperature SmA phase and the helicoidal pitch consequently undergoes critical divergence at the SmA-N* transition.…”

Section: Materials and Devicesmentioning

confidence: 67%

An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

2006

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The phenomenon whereby sudden changes in helicoidal pitch occur in thin chiral nematic devices with strong surface anchoring has been studied experimentally. This has been done with the aim of examining the underlying process in the context of existing theory. Thin devices (,2.5 mm thick) containing two commercially available chiral nematic liquid crystals were employed in the study. The samples were chosen for their dependence of pitch on temperature; one exhibits a very slow increase in pitch with increasing temperature (95.6% of the Merck material BL131 in BL130), while the second shows the more common rapid reduction in pitch with increasing temperature (the Merck mixture TM1001). High resolution reflection spectra were obtained for the devices and a numerical fitting algorithm, based on the Berreman 464 matrix technique, provided accurate information on changes in the pitch, refractive indices, device thickness and changes in the surface director across the pitch jump region. We demonstrate that changes in refractive index and device thickness are negligible in analysis of the reflection spectra across the pitch jumps. We further show that the pitch changes discontinuously at the pitch jump, with no variation in its value as the process occurs. We find evidence that the surface directors also change by less than 10u during this process in a manner analogous to coiling or uncoiling a constrained spring. This mechanism differs somewhat from others proposed in the literature.

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Section: Materials and Devicesmentioning

confidence: 67%

An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

2006

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“…This result elucidates further the physics of the DDLCs since previous works have found that only the adsorption of dyes is responsible for the surface anchoring energy during illumination. [5][6][7][8] For the DDLC cell under sufficient illumination, the surface anchoring energy that is provided by the adsorption of dyes is around double that provided by the preexisting-dye-induced torque. This result indicates that the adsorption of dyes dominates the reorientation of the polar director after illumination.…”

Section: B Calculation and Discussion Of Polar Anchoring Energy Of Dmentioning

confidence: 99%

“…[1][2][3][4] The director reorientation becomes permanent if the excited dye molecules are adsorbed on the boundary surface of the DDLC cell, leading to the alignment of the LC molecules and the appearance of anchoring energy. [2][3][4][5][6] The anchoring energies of the DDLC cells are obtained by measuring using a polarized optical microscope, 5 the pumpprobe twist nematic method 6,7 and measurement of Freedericksz transition. 8 Most studies of DDLC cells have focused on the azimuthal component of the anchoring energy; [5][6][7] few have considered the polar component.…”

Section: Introductionmentioning

confidence: 99%

“…[2][3][4][5][6] The anchoring energies of the DDLC cells are obtained by measuring using a polarized optical microscope, 5 the pumpprobe twist nematic method 6,7 and measurement of Freedericksz transition. 8 Most studies of DDLC cells have focused on the azimuthal component of the anchoring energy; [5][6][7] few have considered the polar component. 8 The polar anchoring energy in the DDLC cell importantly affects the electrooptical properties ͑such as response time and threshold voltage͒.…”

Section: Introductionmentioning

confidence: 99%

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Determination of polar anchoring energy of dye-doped liquid crystals by measuring capacitance

Huang

Cheng

et al. 2010

Journal of Applied Physics

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Polar anchoring energy of a dye-doped liquid crystal (DDLC) cell is determined based on capacity measurements. Experimental results indicate that under the illumination of a pump beam, the polar anchoring energy (7.90×10−6 J/m2) includes the adsorption-induced anchoring energy (5.74×10−6 J/m2) and the preexisting-dye-induced anchoring energy (2.16×10−6 J/m2). The latter is attributed to the torque, which is induced by the dye molecules on the boundary surface even before illumination. After the illumination, the adsorption-induced anchoring energy remains and the preexisting-dye-induced anchoring energy disappears, with the former revealing that weak anchoring affects the decay time and threshold voltage of the DDLC cell. Moreover, plotting the polar angle distributions in the DDLC cell reveals its correlation with variations in the capacitance of the DDLC cell.

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“…In the LCs with azo-dyes, the dye molecules can be either coated on the substrate surfaces of the LC cell [4] or simply doped in the LC material [5,6]. In the case that the azo-dyes are coated on the substrate surfaces, the photo-isomerization process of the dye molecules on the surface predominantly governs the LC alignment which propagates into the bulk.…”

Section: Introductionmentioning

confidence: 99%

Stability of Optical Reorientation of Nematic Liquid Crystals Doped with Azo-Dyes in Polymer Networks

Jang

Lee∗

2004

Molecular Crystals and Liquid Crystals

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We report on the stability of the optical reorientation of doped nematic liquid crystals (LCs) with azo-dyes in polymer networks. The photo-reactive polymer networks formed within the doped LC medium play a critical role in achieving the stable optical reorientation of the LC originating from the trans-cis transformation of the dye molecules. Moreover, the photo-reactive polymer layer on the substrate surface is required to produce the surface memory effect of the dye-doped LC. The optically induced memory is well retained in the dyedoped LC only in the presence of the polymer network medium.

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Laser-induced surface and bulk reorientation of the director in azo-dye-doped liquid crystal cells

Cited by 11 publications

References 24 publications

An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

Determination of polar anchoring energy of dye-doped liquid crystals by measuring capacitance

Stability of Optical Reorientation of Nematic Liquid Crystals Doped with Azo-Dyes in Polymer Networks

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