Deuterium nuclear magnetic resonance spectroscopy and differential scanning calorimetry are used to map the phase boundaries of mixtures of cholesterol and chain-perdeuteriated 1,2-dipalmitoyl-sn- glycero-3-phosphocholine at concentrations from 0 to 25 mol % cholesterol. Three distinct phases can be identified: the La or liquid-crystalline phase, the gel phase, and a high cholesterol concentration phase, which we call the 0 phase. The liquid-crystalline phase is characterized by highly flexible phospholipid chains with rapid axially symmetric reorientation; the gel phase has much more rigid lipid chains, and the motions are no longer axially symmetric on the 2H NMR time scale; the 0 phase is characterized by highly ordered (rigid) chains and rapid axially symmetric reorientation. In addition, we identify three regions of two-phase coexistence. The first of these is a narrow La/gel-phase coexistence region lying between 0 and about 6 mol % cholesterol at temperatures just below the chain-melting transition of the pure phospho- lipid/water dispersions, at 37.75 OC. The dramatic changes in the *H NMR line shape which occur on passing through the phase transition are used to map out the boundaries of this narrow two-phase region. The boundaries of the second two-phase region are determined by 2H NMR difference spectroscopy, one boundary lying near 7.5 mol 5% cholesterol and running from 37 down to at least 30 OC; the other boundary lies near 22 mol 5% cholesterol and covers the same temperature range. Within this region, the gel and /3 phases coexist. As the temperature is lowered below about 30 "C, the phospholipid motions reach the intermediate time scale regime of 2H NMR so that spectral subtractions become difficult and unreliable. The third two-phase region lies above 37 OC, beginning at a eutectic point somewhere between 7.5 and 10 mol % cholesterol and ending at about 20 mol %. In this region, the La and /3 phases are in equilibrium. The boundaries for this region are inferred from differential scanning calorimetry traces, for the boundary between the La- and the two-phase region, and from a dramatic sharpening of the NMR peaks on crossing the boundary between the two-phase region and the &phase region. In this region, the technique of difference spectroscopy fails, presumably because the diffusion rate in both the La- and P-phase domains is so rapid that phospholipid molecules exchange rapidly between domains on the experimental time scale.

Phase equilibria of cholesterol/dipalmitoylphosphatidylcholine mixtures: 2H nuclear magnetic resonance and differential scanning calorimetry.

Foreword. Series Editor's Foreword. Preface. 1. Liquid crystal physics.* Introduction.* Thermodynamics and statistic physics.* Orientational order.* Elastic properties of liquid crystals.* Response of liquid crystals to electro-magnetic fields.* Anchoring effects of nematic liquid crystal at surfaces. 2. Propagation of light in anisotropic optical medium.* Electromagnetic wave.* Polarization.* Propagation of light in uniform anisotropic optical media.* Propagation of light in cholesteric liquid crystals. 3. Optical modeling methods.* Jones matrix method.* Mueller matrix method.* Berreman 4x4 method. 4. Effects of Electric field on Liquid Crystals.* Dielectric interaction.* Flexoelectric Effect.* Ferroelectricity in liquid crystals. 5. Freedericksz transition.* Calculus of variation.* The Fredeericksz transition: statics.* The Freedericksz transition: dynamics. 6. Liquid Crystal Materials.* Introduction.* Refractive indices.* Dielectric constants.* Rotational Viscosity.* Elastic constant.* Figure-of-merits.* Refractive index matching between liquid crystals and polymers. 7. Modeling of liquid crystal director configuration.* Electric energy of liquid crystals.* Modeling electric field.* Simulation of liquid crystal director configuration. 8. Transmissive liquid crystal display.* Introduction.* Twisted nematic cells.* In plane switching (IPS) mode.* Vertical alignment (VA) mode.* Multi-domain Vertical Alignment (MVA) Cells.* Optically compensated bend (OCB) cell. 9. Reflective and Trasreflective display.* Introduction.* Reflective liquid crystal displays.* Transflector.* Classification of Transflective LCDs.* Dual-cell-gap Transflective LCDs.* Single-cell-gap Transflective LCDs.* Performance of transflective LCDs. 10. Liquid crystal display matrices, drive schemes and bistable displays.* Segmented displays.* Passive matrix displays and drive scheme.* Active Matrix Displays.* Bistable ferroelectric liquid crystal displays and drive scheme.* Bistable nematic displays.* Bistable cholesteric reflective display. 11. Liquid crystal/polymer composites. * Introduction.* Phase separation.* Scattering properties of liquid crystal/polymer composites.* Polymer dispersed liquid crystals.* Polymer stabilization liquid crystals.* Displays from liquid crystal/polymer composites. 12. Tunable liquid crystal photonic devices. * Introduction.* Laser beam steering.* Variable Optical Attenuators.* Tunable-Focus Lens.* Polarization-Independent LC Devices. Index.

Fundamentals of Liquid Crystal Devices

▪ Abstract The formation of switchable holographic gratings from polymer-dispersed liquid crystals (H-PDLCs) allows for the development of switchable transmissive and reflective diffractive optics. These structures are created by the coherent interference of laser radiation within a syrup containing photoreactive monomer, initiator, and liquid crystal. Local differences in photopolymerization rates induce phase separation of discrete LC domains to occur periodically commensurate with the period of the interference pattern. These spatially periodic gratings of nano-scale sized LC domains can be formed on grating length scales ranging from 100 nm to microns depending on the optics of fabrication. True Bragg gratings are formed with spacings typically less than 1 μm. Owing to the refractive profile generated by this periodic two-phase structure, diffraction of light occurs. Electrical switching of the average director orientation within the LC domains results in a modulation of diffracted radiation. This tec...

Holographic Polymer-Dispersed Liquid Crystals (H-PDLCs)1

A high intensity light projector for stage, architectural and similar applications includes a controllable image quality projection gate providing advanced visual effects. The projection gate, capable of selectively scattering or transmitting incident light, may be constructed of an array of scattering liquid crystal material in combination with infrared and ultraviolet reduction means which provide in the high intensity beam, a stable thermal environment by minimizing the absorption of light by the projection gate. Additional thermal efficiency is provided by supplemental cooling means. Color control is also provided in the form of dichroic filter wheels forming cooperating adjustable low, high and band width filters including saturation control. A color measuring feedback sensor is also provided. An intensity measuring feedback sensor controls a spatially-modulated, variable-density, reflectively-coated dimming wheel. A programmable gobo system has provisions for gobo selection, orientation, and rotation.

High intensity lighting projectors

An overview over the current state of research in the field of biaxial nematic liquid crystalline materials is given. After a short introduction, providing some general aspects and summarizing the classical approaches, the main part focuses on recent developments of new concepts for designing biaxial nematics. First, the major theoretical concepts are outlined, including the classification to different symmetries, the importance of cooperativity and cluster formation for the development of biaxial order and the conditions for the establishment of field induced and spontaneous biaxiality in nematic phases. These new concepts also require the re-evaluation of the tools used for the identification of phase biaxiality, which are discussed briefly. In the second part, recent progress in the design of potential biaxial nematic materials, especially focussing on bent-core molecules with nematic phases, is reported and, finally, comparisons with phase biaxiality as observed in smectic liquid crystals are made.

Biaxial nematic phases

The response times and operating voltages of light shutters formed from polymer dispersed liquid crystals (PDLCs) have been studied experimentally and the results compared with calculations based on non-sperhically shaped nematic droplet models. The experiments were performed on light shutters with elongated and uniformly aligned droplets where the relaxation time and voltage response were measured. It is shown that the droplet shape can be a dominant factor, particularly for the relaxation time, and the data are compared with equations derived in terms of the aspect ratio of the droplet l = a/b, where a and b are the lengths of the semi-major and semi-minor axes, respectively, of the elongated droplet. It is further demonstrated that the electric field inside the droplet can be considerably smaller than the applied field, due to the conductivity and dielectric properties of the polymer and liquid crystal materials. These data are used to obtain values for the ratio of the conductivities of the p...

Response times and voltages for PDLC light shutters

4 – NMR of Liquid Crystals*

The 2H NMR spectrum of a multilamellar dispersion of 1-myristoyl-2-[14,14,14-2H3]myristoyl-sn-glycero-3-phosphocholine with 1 mol% cholesterol in excess water has been recorded at temperatures between -15°C and 36°C. Motionally averaged quadrupole coupling constants 〈νQ〉 and motionally induced asymmetry parameters η are obtained by spectral analysis. Values of these quantities indicate that, at temperatures below -4°C, any rotational motion of the molecules about their molecular long axis is slow on the NMR time scale. At temperatures immediately above the pretransition these same parameters show that a fast-rotational motion is occurring about the molecular long axis. This rotational motion is hindered in that the molecules flip about a twofold symmetry axis. Between -4°C and the pretransition, spectra appear as the superposition of two powder patterns, one corresponding to the pattern observed below -4°C and the other to the pattern above the pretransition. The relative contribution of the latter increases with temperature until the pretransition is reached. These data have been interpreted in two ways: either the sample between -4°C and the pretransition contains two populations of rapidly and slowly rotating molecules, or there is only a single population of molecules undergoing a 180° flipping motion on the time scale of the NMR measurement. The latter interpretation is more consistent with other experimental findings. At the temperature of the main transition the hydrocarbon chains melt. In the absence of cholesterol, spectra are more complex in that the line shape is reproduced by the superposition of three spectral powder patterns between -4°C and the pretransition and by the superposition of two spectral patterns above the pretransition. It is postulated that these two patterns observed above the pretransition are in direct correspondence to the two ripple structures observed by freeze-fracture electron microscopy in the absence of cholesterol.

Phase transitions in phosphatidylcholine multibilayers

The invention provides a low loss liquid crystal modulator for coloring and shaping a light beam (IB) wherein liquid crystal light modulators (2B, 2G, 2R) provide continuous variation in color and intensity output by controlled scattering; the liquid crystal light modulators (2B, 2G, 2R) comprise addressable sheets of light-wave-length size liquid crystal occlusions in a transparent matrix (21); the modulators (2B, 2G, 2R) employ nematic liquid crystal exhibiting positive dielectric anisotropy; the modulator is employed in varying and coloring output beams (OB) to allow for colored data or video transmission; images produced may vary in time as is required for, e.g., color television; the modulator is employed in color projectors for both data and video projection, for color printing, and for colored stage illumination. Low loss transmission of the modulators (2B, 2G, 2R) provides for bright images which can be viewed under high ambient illumination.

Low loss liquid crystal modulator for coloring and shaping a light beam

Unusual deuterium NMR spectral patterns are reported for a magneto-aligned, smectic-$E$ sample consisting of a binary mixture of 4-$n$-butoxybenzylidene-4\ensuremath{'}-$n$-octylaniline-2, 3, 5, 6-${d}_{4}$ ($4\mathrm{O}.8\ensuremath{-}{d}_{4}$) and 50 wt.% 4-$n$-octyloxycyanobiphenyl(8OCB). This spectral behavior is consistent with the para axis of the aromatic ring of 4O.8 being perfectly ordered ($S=0.99\ifmmode\pm\else\textpm\fi{}0.01$) in the smectic-$E$ phase. The short axis of the ring is also ordered, however, not perfectly ordered, on the average, and undergoing $\ensuremath{\pi}$ flips about the para axis on a time scale \ensuremath{\lesssim} ${10}^{\ensuremath{-}5}$ sec. There are found to be two possible motional models for the orientational ordering of the short axis of the ring that are consistent with the data: (1) molecular diffusion about the herringbone lattice with angular jumps of 44\ifmmode^\circ\else\textdegree\fi{} between lattice sites, or (2) on-site librational motion with an in-plane order parameter of 0.80 for the degree of order of the short axis. Upon transforming from the smectic-$B$ to the smectic-$E$ phase in this material the degree of order of the para axis of the ring is observed to change continuously.

J. William Doane

Papers

Response times and voltages for PDLC light shutters

4 – NMR of Liquid Crystals*

Phase transitions in phosphatidylcholine multibilayers

Low loss liquid crystal modulator for coloring and shaping a light beam

Molecular ordering and motion within the smectic-E phase: 2 H NMR study