Reactive Liquid Crystal Research Articles

Mesomorphic and Orientational Study of Materials Processed by In Situ Photopolymerization of Reactive Liquid Crystals

The synthesis and in situ photopolymerization of reactive liquid crystals for the preparation of materials with different degrees of cross-linking is described. The molecular orientation of polymeric films can be controlled by orienting the monomeric photopolymerizable materials in the mesomorphic state. The birefringence of photopolymerizable materials and the resulting polymers are described, and its dependence on the temperature has been evaluated. The degree of order of polymeric films has been studied by using a reactive nitrostilbene unit as a probe for performing dichroism measurements. Polymeric films with a low degree of cross-linking showed a memory effect, as observed by optical microscopy, X-ray diffraction, and birefringence measurements.

Unusual Odd-Even Effects in Vinyl Ether and Acrylated Direactive Liquid Crystals

Four series of direactive liquid crystals are presented and their physical properties characterised. The core groups are based on either a lateral chloro or methyl terphenyl and the reactive groups are either acrylates or vinyl ethers. It is shown that reactive liquid crystals with vinyl ether reactive groups have higher transition temperatures, birefringence, and order parameter than the corresponding acrylates. Both the vinyl ether and acrylate series show an odd-even effect in transition temperatures, birefringence and order parameters. The odd-even effect in the vinyl ether series is particularly marked.

Chiral nematic order in liquid crystals imposed by an engineered inorganic nanostructure

Control over the orientational order of liquid crystals (LCs) is critical to optical switching and display applications. Porous polymer networks have been used to influence the orientation of embedded chiral liquid crystals1, yielding for example reflective displays. Here we show that inorganic films with a porous structure engineered on the submicrometre scale by glancing-angle deposition2,3 can be used to control the orientation of LCs impregnated into the voids. The inorganic material contains helical columns that orient rod-like nematic LCs into a phase similar to a chiral nematic1,4 but with direct control of the local molecular arrangement (for example, the helical pitch) imposed by the inorganic microstructure. We also show that reactive LC molecules in this composite material can be crosslinked by photopolymerization while retaining the imposed structure.

Photo-Induced Diffusion in Polymerizing Chiral-Nematic Media

Photo-assembly of reactive liquid crystals by simultaneous diffusion and polymerization can give rise to interesting new polymeric architectures. In this report, the authors summarize recent results, which show how deformation of the molecular helix in a cholesteric network can give rise to interesting new optical properties, such as higher order reflection bands and built-in optical retardation. When the deformed helix is combined with a pitch gradient over the film thickness, the built-in retardation can be used for wide-band cholesteric polarizers that directly generate polarized light.

Synthesis and Polymerization of Reactive Chiral Liquid Crystals Bearing a Tetrafluorophenylene in Core Structure

A new reactive fluorinated liquid crystal (1) was synthesized. The thermal behavior was studied by polarizing microscopy and DSC. The monomeric mesogen was polymerized to afford a novel fluorinated side-chain polysiloxane which exhibits liquid crystallinity. The nonfluorinated mesogen and polysiloxane were also synthesized for comparison. The results show that the displacement of phenylene by tetrafluorophenylene causes mesogen to exhibit preferentially nematic mesophase rather than cholesteric or smectic one, and the large polarization in main core section leads mesogen to show the higher smectic mesophase.

Molecular architectures in thin plastic films by in‐situ photopolymerization of reactive liquid crystals

Abstract— The process of in‐situ photopolymerization of reactive mesogens leads to densely crosslinked liquid crystal (LC) networks. The molecular organization within the thin films can be accurately controlled by combining the various alignment techniques known for low molar mass LCs with the structuring techniques known for photopolymerization. The films thus produced exhibit optical properties useful for polarization control and/or colour control in the various types of LCDs.

Rigid rod molecules as liquid crystal thermosets. II. Rigid rod esters

AbstractNine rigid rod ester monomers endcapped with maleimide, nadimide, and methylnadimide groups were prepared and studied by DSC and hot stage polarized light microscopy. All of the monomers showed thermotropic nematic liquid crystalline phases and could be thermally crosslinked in the nematic phase. The nematic texture was maintained in the crosslinked solid state. The nematic phase range was enlarged by B‐staging the monomeric compounds. Heating the monomers for a short period of time in the nematic phase lowered the crystal to nematic transition temperatures and increased the nematic to isotropic transition temperatures. A nonequilibrium phase diagram was proposed to explain the melting behavior of these reactive liquid crystal thermoset materials.