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Hydrophobic polymer films, having an aqueous phase distributed throughout the matrix, were formed by polymerizing a solution of dodecyl acrylate and 1,6 hexanediol diacrylate containing nanometer-sized drops of water stabilized by sodium bis(2-ethylhexyl) sulfosuccinate (AOT). Photopolymerization-induced aggregation of the water drops and/or phase separation occurred, as the initially clear solutions became opaque films. The polymerized films became clear, as the relative humidity was reduced. Clear films still contained 20–50% of the initial water. The transition from opaque to clear films was reversible provided that the film did not become completely dry and form cracks. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

The physical and mechanical properties of several thiol–ene based polymers and their mixtures with the liquid crystal, E7, were characterized to probe their relationship with the liquid crystal film electro-optic performance properties. Kinetic data suggests that high conversion is achieved for each thiol–ene combination. Pre-polymerization phase diagrams indicate that each thiol–ene/E7 mixture phase separates well below room temperature, and thus prior to polymerization at room temperature all are in a single phase. Holographic polymer dispersed liquid crystals (HPDLC) were fabricated for several thiol–ene and E7 mixtures, and electro-optical parameters characterized to probe the relationship between the thiol–ene network properties and the electro-optic performance of the HPDLCs. The photocured matrices exhibited glass transitions and tan δ peak maxima that ranged from temperatures below 0 °C to well above room temperature. There is a clear correlation between the physical nature of the matrix and the electro-optic switching parameters with H-PDLC films fabricated from trithiol-pentaerythritol triallylether, all of which exhibit glass transition temperatures below 0 °C, having the fastest switching times and lowest switching voltages at room temperature. Also, in each case higher liquid crystalline concentration resulted in lower switching voltages.

We report on the morphological and thermal properties of polymer-dispersed liquid crystals (PDLCs) fabricated with frontal-polymerization-induced phase separation (FPIPS). Frontal polymerization is characterized by a rapid-conversion, high-temperature, and large-thermal-gradient environment. A comparison is made between the morphological and thermal properties of PDLCs fabricated with FPIPS and traditional thermal-polymerization-induced phase separation. Characterization includes differential scanning calorimetry to probe the glass and nematic-to-isotropic transitions and scanning electron microscopy to evaluate the phase-separated morphology. In addition, the frontal temperatures and velocities are reported for PDLCs fabricated with frontal polymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 204–212, 2003

When low-molecular weight liquid crystals are confined to small cylindrical volumes of porous polymer membranes, the elastic deformation energy and surface boundary effects play an increasing role as the surface-to- volume ratio is increased. For such materials confined to micron-sized volumes the free energy associated with the surface competes with the elastic deformation part of the free energy to determine the molecular organization or director configuration within the volume. An additional contribution to the free energy occurs when external fields are applied to such a system.

Liquid crystalline mixtures of mono- and dimethacrylates [CH 2 =C(CH 3 )COO(CH 2 ) 6 OPhCOO] 2 Ph and CH 2 =C(CH 3 )COO(CH 2 ) 6 OPhCOOPhX (X= CN, OC 6 H 13 ) were photopolymerized after macroscopic orientation of the monomers under a relatively weak magnetic field or via interaction with a unidirectionally rubbed polyimide substrate. Polymerization kinetics was followed by a thermoanalysis technique, and the transmitted light intensity was measured in real time. The macroscopic order parameter of the component comonomer bearing a cyano group incorporated into the polymer network prepared under different conditions was evaluated using IR dichroism. The results obtained for the cross-linked polymer network produced under the low strength magnetic field are compared with those for the polymer film produced by surface orientation

Light‐scattering and transmission properties of aligned nematic droplets dispersed in a solid polymer are studied. Theoretical evaluations of the differential and total cross sections are performed in the anomalous diffraction approximation. The corresponding attenuation coefficients are calculated in a single scattering approximation. The effect of interdroplet interference is discussed as well. Theoretical calculations are in agreement with experimental data obtained from thin films of polymer dispersed nematic droplets of micron size, aligned by an applied electric field.

Liquid crystal and polymer dispersions (LCPD) have potential application as flat panel displays, switchable lenses, optical switches, Bragg gratings, photonic crystals, diffractive optics, hyper-spectral filters, and etc. Precise morphological control of the phase-separated morphology of LCPDs is required to meet the rigorous requirements for the numerous applications. Liquid crystal and polymer dispersions (LCPDs) are micro or nano-structured materials fabricated using one of several phase separation techniques. The micro- or nano-structured morphology of LCPDs ranges from a polymeric network suspended in a liquid crystal solvent (polymer stabilized liquid crystals [PSLC] to random or spatially periodic micron or sub-micron sized liquid crystal droplet dispersions in a solid polymer matrix of polymer dispersed liquid crystals (PDLC) and the holographically formed PDLC (H-PDLC). The goal of this investigation is to identify the material properties and processing conditions required for more precise control of the phase-separated morphology of PDLCs. The investigation entailed construction of thermal phase diagrams for liquid crystal and monomer/pre-polymer mixtures to identify the compositionally dependent phase separation temperatures. The investigation also entailed inducing phase separation of the mixtures via ultra-violent light initiated polymerization at carefully chosen cure temperatures based on the thermal phase diagrams. The phase-separated morphology was correlated with the cure temperature, liquid crystal component, and mixture composition.

This paper investigates the effects of cure temperature and composition on the morphology of polymer dispersed liquid crystals (PDLCs) composed of the liquid crystal, K21 (4-heptyl-4'-cyanobiphenyl), in a thiol-ene based pre-polymer. PDLCs are composites composed of micron-size liquid crystal droplets dispersed in a solid polymer matrix. The PDLCs were fabricated by photo-initiated, polymerization induced phase separation using a differential photo-calorimeter (DPC). The cure temperatures were chosen based on the temperature-composition phase diagrams of the liquid crystal/pre-polymer mixtures. The characterization of the PDLCs included differential scanning calorimeter (DSC) to determine the nematic-to-isotropic transition temperature (TNI) of the liquid crystal and the glass transition temperature (Tg) of the polymer matrix. Scanning electron microscopy (ESEM) was used to examine phase separated morphology.

We have investigated the single components and binary component mixtures of the liquid crystal E7 in NOA65 and UV1 thiol-ene pre-polymers. E7 is composed of K15 (4-pentyl-4'- cyanobiphenyl), K21 (4-heptyl-4'-cyanobiphenyl), M24 (4- octyloxy-4'-cyanobiphenyl), and T15 (4-pentyl-4'- cyanoterphenyl). The single liquid crystal components and binary liquid crystal mixtures that were investigated include K15, K21, K15-K21, K15-M24, and K21-M24. The liquid crystal/pre-polymer phase diagrams were developed using thermally induced phase separation to determine the temperature of phase separation. Then, PDLC samples were prepared using photo-polymerization induced phase separation, and were polymerized at varying increments above the liquid crystal/pre-polymer phase separation temperature to determine how the morphology changes with the polymerization temperature, the liquid crystal component, and liquid crystal percentage. Polarized optical microscopy was used to determine the phase separation temperatures for the liquid crystal/pre- polymer samples and the nematic-to-isotropic transition temperatures for the PDLC samples. Laser light transmission measurements were performed to determine the electro-optic properties of the PDLC samples.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Polymer dispersed liquid crystal (PDLC) materials are produced in a microgravity environment to investigate the gravitationalinfluence on the phase separated microstructure. PDLC materials contain a dispersion of micron-sized liquid crystal dropletsdispersed in a solid polymer. The dispersion is achieved by one of several phase separation methods. The phase separatedmicrostructure determines the operating parameters of PDLCs; therefore, a fttndamental understanding of phase separationprocesses is critically importance. Preparation of PDLC materials in a microgravity environment is advantageous forstudying the underlying processes ofphase separation that are masked in our terrestrial environment. We investigate the effectofgravity on the microstructure of PDLC materials using photo-polymenzable materials aboard NASA's KC435 aircraft. Keywords: liquid crystal, phase separation, microgravity INTRODUCTION Polymer dispersed liquid crystals (PDLC) are promising new materials for spatial light modulators in projection displaysystems, vision products, optical interconnects for non-destructive testing applications, optical data storage, tunable reflectivedisplays, dynamically variable lenses, fiber optic switches, and attenuation of high intensity laser radiation. PDLC materialsoperate on the principle ofelectrically controllable light scattering. A normal mode PDLC is highly scattering in the OFF-stateand is highly transparent in the voltage applied ON-state. The weight percentage of liquid crystal in a PDLC material rangesfrom 30% to above 90%. The global microstructure is dependent on the weight percentage of liquid crystal in the initialmixture. Typically, a droplet dispersion is obtained when the liquid crystal is the minor component; and the polymericmembrane niicrostructure is prevalent when the liquid crystal is the major component. The critical operating parameters whichdetermine the successfl.il application ofPDLC materials are contrast, switching voltage, and switching time. PDLC switchingtimes range from sub-miffisecond to hundreds of milliseconds. The switching voltage and switching time depend on thefrequency dependent dielectric properties of the liquid crystal and polymer, the anchoring interaction at liquid crystal andpolymer interfaces, and the liquid crystal ordering.

A trimolecular liquid crystalline mixture of monomers was photopolymerized while being subjected to macroscopic orientation via surface contact or continuous application of a magnetic field. Polymerization kinetics were not influenced by the macroscopic orientation, and crosslinked networks were rapidly produced. Both IR dichroism measurements and x-ray diffraction analysis indicated that oriented networks were generated when polymerization was conducted from a nematic phase.

In order to obtain oriented liquid crystalline films which maintain the alignment of monomeric species from whence they are derived, it is necessary to induce rapid, isothermal polymerization processes. In recent studies, monofunctional and difunctional mesogenic methacrylate monomers with nematic and smectic phases have been aligned and polymerized to yield macroscopically oriented polymers. In some cases, the orientation is maintained even after the polymer is heated above its clearing temperature. By utilizing a thin-foil calorimeter, we have succeeded in measuring polymerization rates in macroscopically oriented liquid crystalline monomers. Although the macroscopic structure of the aligned system may be locked-in during polymerization, this does not necessarily result in enhanced rates compared to non-oriented samples. The experimental techniques used to measure the polymerization exotherms of oriented liquid crystals are described. Initial results which illustrate the effect of macroscopic alignment are discussed with respect to polymerization kinetic rates. Implications for polymerization of oriented liquid crystals are briefly discussed in the context of optical properties of the final films.

— Liquid-crystal and polymer dispersions are typically made utilizing one of three methods of phase separation. Laser light scattering is a convenient method to probe the evolving supra-nano scale and micron scale morphology of phase-separating mixtures. We used laser light scattering to probe the evolving supra-nano and micron scale structure of phase-separating liquid crystal and monomer mixtures induced with photon-initiated polymerization. We report on the evolutionary phase separation for mixtures of the E7 and the thiol-ene based optical adhesive Norland 65 from low to high weight percentages of E7.

An overview of polymer dispersed liquid crystal (PDLC) materials, their physical properties, and potential applications in the optic and electrooptic industry is presented. These optoelectronic materials have unique properties which are expected to expand liquid crystal technology into new display and light shutter applications. Recent research by small and large industrial and university laboratories on device physics and chemistry has provided substantial progress towards the commercialization of these materials. Work to date on such features as response times, switching voltage, and contrast as well as material preparation procedures and unique optical characteristics will be reviewed. These materials are also of interest to basic physics because of new kinds of physical phenomena brought on by the confinement of a nematic liquid crystal to small submicron-size droplets. Enhanced surface-to-volume ratio, large nematic deformations and problems associated with molecular anchoring at a polymer w...

The light transmission and scattering properties of a PDLC light shutter in the transparent (field applied) state are studied. It is found from transmission experiments of samples containing sub-micron size droplets that there is a broad distribution of about 10° about the field direction in droplet alignment, even in saturating fields. Evidence is presented that this distribution is principally caused by the non-spherical shape of the droplets. Measurements of the total scattering cross section imply that even in the transparent state there exists some multiple scattering or interdroplet scattering effects. Transmission and scattering measurements in samples with supra micron size droplets show effects of anomalous diffraction and are sensitive to distributions in droplet size. The theory of scattering from a nematic droplet in the anomalous diffraction regime agrees favorably with experiment.