The performance of a polymer-stabilized blue phase system based on a nematic host with large dielectric anisotropy and a chiral dopant with high helical twisting power is investigated and the influence of the reactive monomer composition on the electro-optic characteristics is studied. Field-induced birefringence with a Kerr coefficient greater than 1 nm V−2 can be achieved in a large temperature range from well below 20 °C to above 55 °C. The disturbing influences of electro-optic hysteresis and memory effects can be reduced by diligent choice of the composition and appropriate electric addressing.
In photoreactive liquid crystals, spontaneous pattern formation can be used to fabricate phase gratings or polymer films with a periodic surface modulation. Typically, the periodicity of such structures is comparable to the sample thickness, and thus in the range between several micrometers and about 100 μm. Here, attempts to create and to investigate smaller structures are presented. For a chevron pattern, periodicities as small as 800 nm could be detected.
Mixtures of a non-reactive and a photo-reactive liquid crystal, both consisting of bent core molecules, were used to prepare polymer-stabilized antiferroelectric liquid crystal cells by in-situ photo-polymerization. The mixtures exhibit a larger temperature range of the antiferroelectric phase than the pure compounds. The polymer network improves the ability of uniform alignment and thus enhances the switching contrast. In addition, the polymer-network reduces the switching times, in particular the relaxation time from the field-induced state to the ground state.
Reversible optical control of transmittance in polymer/liquid crystal composite films by photoinduced phase transitionElectrically induced dissipative structures in liquid crystals can be stored by the photocuring of reactive mesogens. Thus, spontaneous pattern formation can be used to fabricate phase gratings or polymer films with a periodic surface modulation from an initially uniform sample. Different patterns, both in the conductive and in the dielectric regimes, have been stored. Photopolymerization and subsequent investigation by atomic force microscopy provide a useful tool in analyzing dissipative structures, even if the lattice constants are smaller than 1 m. This method indicates surface modulations with amplitudes of up to 12 nm and periodicities between 800 nm and several tens of micrometers. The influences of composition and curing conditions on the topography have been studied.
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