Hysteresis Behavior of Texture in the Field-Induced Nematic-Cholesteric Relaxation

Abstract

The effects of bias voltages on the field-induced nematic-cholesteric relaxation are investigated both for samples with perpendicular boundaries and for ones with parallel boundaries, and are discussed in relation to the hysteresis behavior of texture. When the applied voltage is reduced from a value above the threshold to a bias voltage below the threshold a relaxation from the field-induced nematic to a Grandjean-like cholesteric state occurs, the relaxation time of which increases as the bias voltage approaches a certain value Vc↓; the ratio of Vc↓ to the threshold voltage Vc for cholesteric-to-nematic transition is about 0.5 irrespective of the boundary conditions. When the bias exceeds Vc↓, the transformation shows a hysteresis behavior such that the nematic state is kept for a long time until gradually replaced by focal conic domains nucleating from some local defect points; the boundary condition is found to play no essential role in the hysteresis behavior. An interpretation of the results is presented.

Direction switching and beam steering of cholesteric liquid crystal gratings

“…Notably, the transient planar state is a meta-stable state with the effective pitch P* ¼ (K 33 /K 22 )P 0 . 10,14 For the LCs used in this experiment, the P* is about 2 times higher than P 0 ; hence, the d/P* is $0.5. As the result, the electrical switching of the stripes' direction can be understood, since the director direction of the LC molecules in the middle layer, which determines the strip direction is parallel (perpendicular) to the rubbing direction in planar (transient planar) zone.…”

Simultaneous red–green–blue reflection and wavelength tuning from an achiral liquid crystal and a polymer template

“…[1,2,7,8] Unwinding of the helix using an electric field perpendicular to the helix axis can lead to a change in the wavelength of the reflection band and thus some color tuning, but such an approach requires fringe-fields that can locally distort and disrupt the homogeneity of the structure. [9,10] The Helfrich deformation, [11,12] has also been shown to provide a means of changing the wavelength of the reflection. However, a marked deterioration in the quality of the macroscopic helix can result due to the presence of EHDIs.…”

Electrical and optical switchings of the direcitons of cholesteric liquid crystals gratings

“…As shown in Fig 2(a), the initial state is a homeotropic state, in which the CLC twist has been completely unwound. Then the electric field is turned off, the sample transits to CLC transient planar state [9][10][11][12][13][14] at the early stage and returns to the planar state with time ( Fig. 2(b )).…”