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1.
Liquid crystals (LCs) and polymers are extensively used in various electro-optical applications. In this paper, normal mode polymer stabilized cholesteric LC film is prepared and studied. The effects of chiral dopant and monomer concentrations on the electro-optical properties, such as contrast ratio, driving voltage, hysteresis width and response time, are investigated. The reasons of electro-optical properties influenced by the concentrations of the materials are discussed. Through the proper material recipe, the electro-optical properties of polymer stabilized cholesteric LC film can be optimized. 相似文献
2.
Experiments have shown that cholesteric droplets or cholesteric fingers may be put into motion by the action of an electric
field. The former rotate whereas the latter drift perpendicularly to their axes. In all cases, the texture moves without visible
material transport. The electric Lehmann effect was initially used to interpret these observations but, recently, alternative
explanations were found, based on electrohydrodynamics. Another experiment in this area was that of Padmini and Madhusudana
(Liq. Cryst. 14, 497 (1993)). Performed in 1993 with a compensated cholesteric liquid crystal under fixed planar boundary conditions, it
was also explained in terms of electric Lehmann effect. We conducted the same experiment and extended it to a π -twisted planar
geometry. Although our experimental results agree with those of Padmini and Madhusudana, we demonstrate that they are incompatible
with an electric Lehmann effect. By contrast, an explanation based on flexoelectricity allows us to interpret the whole data
set obtained in both geometries. The consequence is that there is at the moment no clear experimental evidence of the electric
Lehmann effect. 相似文献
3.
4.
We continue the study of U(1) vortices with cholesteric vacuum structure. A new class of solutions is found which represent global vortices of the internal spin field. These spin vortices are characterized by a non-vanishing angular dependence at spatial infinity, or winding. We show that despite the topological Z2 behavior of SO(3) windings, the topological charge of the spin vortices is of the Z type in the cholesteric. We find these solutions numerically and discuss the properties derived from their low energy effective field theory in 1+1 dimensions. 相似文献
5.
We studied the formation of χ disclination lines in planar cholesteric samples placed in a temperature gradient near the cholesteric
to smectic A phase transition. We observed that the first simple line which forms close to the smectic-cholesteric front zigzags
when it is perpendicular to the direction of planar anchoring and is straight for other orientations. This instability is
similar to Herring instability for crystalline surfaces. We show numerically that it originates from a strong increase of
the elastic anisotropy close to the transition. In addition, we propose a new method to measure the pitch divergence at the
smectic to cholesteric phase transition. 相似文献
6.
We report a study of the cholesteric phase in monodisperse suspensions of the rodlike virus fd sterically stabilized with the polymer polyethylene glycol (PEG). After coating the virus with neutral polymers, the phase diagram and nematic order parameter of the fd-PEG system then become independent of ionic strength. Surprisingly, the fd-PEG suspensions not only continue to exhibit a cholesteric phase, which means that the grafted polymer does not screen all chiral interactions between rods, but paradoxically the cholesteric pitch of this sterically stabilized fd-PEG system varies with ionic strength. Furthermore, we observe that the cholesteric pitch decreases with increasing viral contour length, in contrast to theories which predict the opposite trend. Different models of the origin of chirality in colloidal liquid crystals are discussed. 相似文献
7.
V. S. Sutormin I. V. Timofeev M. N. Krakhalev O. O. Prishchepa V. Ya. Zyryanov 《Bulletin of the Russian Academy of Sciences: Physics》2017,81(5):602-604
The reorientation of a cholesteric liquid crystal with a large helical pitch induced by the electric field–driven modification of surface anchoring is investigated. In the initial state, the liquid crystal cell has a homeotropic alignment of the director. An applied dc electric field produced a twisted homeoplanar structure of the cholesteric. 相似文献