Critical Field Strength in an Electroclinic Liquid Crystal Elastomer

We elucidate the polymer dynamics of a liquid crystal elastomer based on the time-dependent response of the pendent liquid crystal mesogens. The molecular tilt and switching time of mesogens are analyzed as a function of temperature and cross-linking density upon application of an electric field. We observe an unexpected maximum in the switching time of the liquid crystal mesogens at intermediate field strength. Analysis of the molecular tilt over multiple time regimes correlates the maximum response time with a transition to entangled polymer dynamics at a critical field strength.Comment: 4 pages, 3 figure

Orientational order of a ferroelectric liquid crystal with small layer contraction

We present spectroscopic and optical studies of a non-layer-shrinkage ferroelectric liquid crystal DSiKN65. The orientational order parameters S, measured with respect to the smectic layer normal using IR spectroscopy on a sample aligned homeotropically, does not exhibit any significant variation between the smectic-A* and smectic-C* phases. In contrast the birefringence of a planar homogenous sample abruptly increases at the smectic-A* to smectic-C* transition. This suggests a general increase in the orientational order, which can be described by the orientational order parameters S\u27 defined with respect to the director. Simultaneous increase of S\u27 and the director tilt θ may explain the low shrinkage of smectic layers, which is consistent with recent theoretical models describing the smectic-A* to smectic-C* transition for such materials

Strain Analysis of a Chiral Smectic A Elastomer

We present a detailed analysis of the molecular packing of a strained liquid crystal elastomer composed of chiral mesogens in the smectic A phase. X-ray diffraction patterns of the elastomer collected over a range of orientations with respect to the X-ray beam were used to reconstruct the three-dimensional scattering intensity as a function of tensile strain. For the first time, we show that the smectic domain order is preserved in these strained elastomers. Changes in the intensity within a given scattering plane are due to reorientation, and not loss, of the molecular order in directions orthogonal to the applied strain. Incorporating the physical parameters of the elastomer, a nonlinear elastic model is presented to describe the rotation of the smectic-layered domains under strain, thus providing a fundamental analysis to the mechanical response of these unique materials.Comment: 28 Page

Novel ferroelectric liquid-crystalline polymers with fast electro-optic switching times

The synthesis and ferroelectric properties of several novel liquid-crystalline polymers are presented. By manipulating the number of side-group mesogens attached to the polysiloxane backbone, it has been possible to achieve many significant properties: large range of the ferroelectric smectic C<SUP>∗</SUP> phase extending to sub-ambient temperatures, spontaneous polarization values up to 300 nC/cm<SUP>2</SUP> at the lowest temperatures, and bistable electro-optic switching times approaching 100 μs near the smectic C<SUP>∗</SUP>-smectic A transition temperature. These properties are attractive from the point of view of display applications

Photo-dimerized monolayer (PDML) versus rubbed polyimide (RPI): a comparison of electro-optic properties

Electro-Optic response characteristics as well as polar anchoring energies of liquid crystal cells prepared using a new photo-alignment technique i.e., photo-dimerized monolayer, have been measured. These data are compared with those for cells that use a rubbed polyimide alignment layer. The two alignment methods yield comparable electro-optic properties showing thereby that the new photo-alignment technique is a viable alternative to the rubbed alignment technique for display applications

Molecular structure and pretilt control of photodimerized-monolayers (PDML)

We have studied the alignment of nematic liquid crystals on photo-sensitive chemisorbed monolayers. Surface modification and a single UV exposure at normal incidence resulted in photo-dimerized monolayers. A uniform, planar alignment of liquid crystals is realized on these surfaces. Chemical modification of the photo-sensitive chromophores of the monolayer allow fine-tuning of the pretilt. For a given alignment layer, there is a good correlation between the value of the pretilt and the polar properties of the liquid crystal used. Furthermore, the value of the pretilt depends on the chemical functionality at the outermost portion of the photo-alignment layer

Langmuir films of liquid crystalline materials: the influence of molecular architecture on morphology and properties

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