We probe the mesophase transitions and layer structures in thin ordered smectic liquid crystalline elastomer films by means of x-ray diffraction and optical microscopy. Oriented elastomer films of submicrometer thickness are produced by crosslinking freely suspended smectic polymer films. After crosslinking, the mesomorphism is similar to that of the precursor polymer. Smectic layers align parallel to the film plane. The layer spacing increases with temperature in the SmC* phase while it decays above the SmC*-SmA transition.

Molecular films of amino propyl triethoxy silane (APTES) attached with cinnamoyl moieties were deposited on indium tin oxide (ITO) coated glass and quartz substrates by self-assembly technique. The deposition of the monolayer films resulted in a large change in the wettability of the substrates. X-ray photoelectron spectroscopy (XPS) and UV-spectroscopy were used to study the structure and properties of the grown films. The molecular assembly was photodimerized by irradiating it with a linearly polarized UV-light. Thus created polymer-solid interface has been shown to produce good, stable planar orientation of ferroelectric liquid crystal mixtures. The electro-optical and switching properties of the ferroelectric liquid crystal cells have been investigated and found to be quite similar to those prepared in conventional manner.

Reactive mesogenes posess polymerizable groups attached to a rigid, liquid crystalline core. From such molecules, densely crosslinked networks in which the liquid crystalline order is permanentely fixed can be formed by photopolymerization.

Our major synthetic goal was the formation of glass forming reactive mesogenes. Such compounds do not crystallize upon cooling but vitrify and form supercooled LC-phases ('LC-glasses'). They exhibit broad LC-phases and enable us to carry out photopolymerization in a broad range of temperatures.

We have systematically investigated how the topology of the reactive mesogenes influences the stability of the resulting glasses. Comparing twin molecules with three- and four-armed stars we found that the supercooled LC-phase in the three-armed stars has a stability superior to both twin molecules and four-armed stars. In the three-armed star Triple-4 with a suitable substituent pattern the supercooled LC-phase is stable at room temperature for at least nine months. Doped with suitable chiral molecules the glass forming nematics form cholesteric phases which were used for cholesteric polymer networks and for polarization holograms with one s-and one p-polarized writing beam.

Furthermore we have extended our synthetic efforts to reactive mesogenes with three or five conjugated fluorene units as LC-core. After orientation, the mesogenes were photocrosslinked and used as active layer in OLEDs that emit highly polarized blue light.

Illumination of photochromic liquid-crystalline (PCLC) copolymer films with polarized light during the mesophase formation has been studied. Both thick pressed and thin spin-coated, the films show prominent increase in photoinduced orientation, as compared with conventional isothermal photorecording. Two methods of the thermoassisted recording have been suggested, one of those with simultaneous cooling of the film and another one after a shock heating and quenching. The photoinduced birefringence, Δnind, and the order parameter of photochromic groups, Sazo, have been measured. The thermally assisted recording produces holographic gratings with high diffraction efficiency, η, up to 20-30%.

The synthesis of multipodes based on substituted ferrocene groups and the results of the investigations of the liquid-crystalline phase properties of these materials, determined by optical polarising microscopy DSC and X-ray diffraction studies as central cores is reported.

Some linearly conjugated liquid crystals with birefringence greater than 0.4 are discussed. UV stability of these high birefringence liquid crystals was systematically investigated. Both electronic conjugation and molecular structure make essential contributions to the observed degradation phenomena. Guidelines for designing stable high birefringence liquid crystals for displays and optical communications are discussed.

A new family of light-controllable chiral photochromic multifunctional liquid crystalline (LC) side-chain acrylic polymers consisting of nematogenic, chiral and photochromic monomer units was obtained. The new principle of photoregulation of the helical supramolecular structure and optical properties of the binary and ternary chiral photochromic LC polymers based on the change of helical twisting power of the chiral photochromic monomer units was developed. The features of photooptical behaviour of LC polymers possessing the dual photochromism and the peculiarities of optical data recording based on the photochemical spectral gap burning were presented and discussed. The synthesized polymers are shown to be promising candidates for colour data recording and storage.

The synthesis of the first inorganic-organic hybrid liquid crystal dendrimers based on carbosilazane cores, which exhibit enantiotropic nematic and smectic C and columnar phase behaviour is presented and the liquid-crystalline phase properties and the phase structures are discussed.

Obtaining spontaneous orientation and fast collective response of ultra thin liquid crystalline (LC) layers to external stimuli without memory effects, is one of the major challenges in achieving the next generation of LC devices. The relationship between interfacial energies, structure and dynamics of support layers and their effects on surface orientation of liquid crystals has been investigated. A model polymeric system, containing a mesognic group, α- methylstilbene as anchoring group, bridged by an energy controlling moiety, fluorocyclobutyl, has been used to obtain substrates with controlled surface energy and structure. Neutron reflectivity was used to study the surface structure of the polymer. The orientation of a well characterized liquid crystal, 8CB that exhibits both nematic and Smectic phases, was studied by optical microscopy and small angle X-ray scattering. Correlation between the surface structure of the polymeric layer and the orientation of the Smectic phase indicated direct correlation between the surface orientation and the concentration of fluorine at the interface.

This study focuses on the photo-polymerization of a fluorinated monoacrylate monomer and aliphatic analog within a room temperature smectic liquid crystal (LC) in an effort to understand how factors such as LC order, monomer segregation, and monomer chemical structure affects the polymerization mechanism in polymer stabilized liquid crystalline systems (PSLC). Specifically, a fluorinated monoacrylate exhibits significantly enhanced polymerization rates when compared to an aliphatic monoacrylate. Moreover, this rate enhancement is particularly pronounced in the smectic phase of the LC, where the fluorinated monoacrylate displays a polymerization rate in the smectic phase that is over three times faster than the aliphatic monoacrylate in the smectic phase. Also the fluorinated monoacrylate exhibits enhanced segregation between the smectic layers of the LC both before and after polymerization, whereas the aliphatic monoacrylate phase separates during polymerization. The results of this study demonstrate how changes in the monomer chemical structure (i.e. fluorination) can significantly impact the polymerization mechanism and segregation in polymer stabilized systems. This study also offers the potential to further the understanding of tailoring these unique systems for display applications.

We introduce and explore two- and three-dimensional lattices formed in Holographic-Polymer Dispersed Liquid Crystals (H-PDLC) materials, which exhibit an electrically controllable index modulation in multiple dimensions. As electro-optically active holograms, these materials exhibit fast dynamic switching phenomena (~100 microseconds), and are simple to fabricate. While many applications have been proposed for these materials, almost all are based on one-dimensional index modulations in various grating regimes. However, constraints in additional dimensions lead to a much greater sensitivity of the polymer morphology to monomer functionality, exposure irradiance, and grating pitch. In an effort to begin to understand this relationship, two-dimensional triangle lattices were created using two monomeric blends exposed over a range of powers. Final diffraction efficiency (Bragg regime), saturation voltage, and polymer morphology were examined from the resulting triangle lattices. Three-dimensional lattices are discussed and a six-beam holographic method is proposed. Photonic crystal applications are envisioned where the pseudo-bandgap can be electrically controlled.

Numerous studies [1-3] have shown that chiral biological structures share common properties with liquids crystals, in particular a tendency to assemble in three-dimensional lattices very similar to that of chiral nematics. Biological fibrous composites are usually found in planar (film) and cylindrical (fibber) twist geometries. In this work, the formation process of the planar twist architecture is numerically investigated using a mesoscopic model based on the Landau-de Gennes theory of chiral nematic liquid crystals. The simulations and visualizations of the computed textures provide new information on some of the principles that govern the formation of chiral biological structures. It is found that a defect-free planar twist architecture arises from a chiral front propagation process with a fully relaxed wake.

The synthesis of a novel discotic liquid crystal monomer was carried out based on vinyl monomer whose molecular architecture consists of a triphenylene as central core and the peripheral cores were linked to the central core through an alkyl chain spacer. Consequently, a disk-like poymerizable monomer 2, 3, 6, 7, 10, 11-hexakis-[11-(4-{4-(acryloxy)phenylazo}phenoxy)undecanoxy]triphenylene was prepared by using a ferric chloride oxidation method. Polarizing optical microscopy and DSC analysis shows that the monomer exhibited a wide columnar mesophase. UV-vis spectra of the azobenzene mesogens showed that a significant tailing, which would allow the use of laser in the visible range to photoinduce isomerization and reorientation of the azo groups.

We present a computer simulation of the voltage-dependent orientational ordering of a nematic liquid crystal within the lattice approximation, confined between two substrates with different anchoring for each surface. The system is studied by analyzing the response of the molecular reorientation near the surfaces as a function of the applied voltage. The model considers a molecular interaction responsible for the nematic phase that includes a superposition of the anisotropic induced-dipole-induced-dipole and isotropic Maier-Saupe interactions, whereas for the nematic-surface intermolecular interaction we assume the Rapini-Papoular form. The response to the external electric field is studied by calculating the dielectric constant tensor, based on a model through the molecular polarizability. We particularly discussed the case for negative dielectric anisotropy that could have relevance for the voltage controlled twist effect. The simulation is carried through a numerical relaxation method for the total energy of the system.

We describe a method of fabricating microporous films through pattern photopolymerization induced phase separation in a mixture of solvent/monomer using multi-wave mixing, i.e., four-wave mixing through interference of two horizontal and two vertical waves. The simulation on the microporous forming process was undertaken in the framework of the time-dependent Ginzburg-Landau (TDGL) Model B equations coupled with the reaction kinetic equation of photopolymerization. In the total free energy description, Flory-Huggins free energy of mixing was combined with the elastic free energy of the network. The calculated results showed that the microporous size, shape, and spacing of the micropores depend on the angle of interference and the reaction rate controlled by the incident UV intensity.

The ability to realise frequency agile filters has always been a major goal of materials and device scientists. Polymer dispersed liquid crystal materials (PDLCs), in which the droplets are deliberately produced with dimensions smaller than the Rayleigh limit for optical scatter, provide a means of realising this goal. At visible wavelengths the material has the appearance of a phase-homogeneous medium both with and without applied electric field. Refractive indices are an average of those of the liquid crystal and those of its host and can be described on the basis of effective medium approximations using orientationally averaged values for the randomly aligned LC material for the ambient state. On application of electric field, the individual liquid crystal molecules align with a resulting reduction in the effective index of the medium. Extensive studies of the variation of process parameters and their effect on the morphology of the composite have enabled field induced changes in refractive index in excess of 0.05 to be achieved without recourse to the use of polarisers and with little or no hysteresis effects. At wavelengths associated with WDM devices for telecommunication applications, the degree of scatter loss is negligible. Design trade-offs have been assessed for candidate tunable WDM filters based on resonant cavity devices.

A novel composite system containing of liquid crystalline semiconductor and crosslinked polymer exhibited high hole mobilities with comparison of that of pure liquid crystalline molecules. The carrier transport properties were influenced by the polymerized conditions. The mobilities were independent on temperature and electric field in the case of mesophases polymerized samples. These carrier transport properties were essentially different of those of well-known molecularly doped polymers.