Optical shutters whose operation is based on the Kerr effect, which is a quadratic electro-optic effect generated in optically isotropic substances, have extremely fast response times. However, the magnitude of the induced birefringence in conventional Kerr materials is too small for them to be used in flat-panel displays. We show that a polymer-stabilized blue phase has a Kerr constant which is about 170 times larger than that of nitrobenzene. We also demonstrate microsecond electro-optical switching over a wide temperature range for flat Kerr cells containing the polymer-stabilized blue phase. These achievements can contribute to providing fast-response flat-panel liquid-crystal displays that need not undergo a rubbing process during manufacture.The Kerr effect is the development of birefringence in an optically isotropic substance, such as a liquid, when the substance is placed in an electric field. The magnitude of the birefringence induced via the Kerr effect, Dn, can be expressed bywhere Dn is the induced birefringence, k is the wavelength of light, and K is the Kerr constant. The Kerr cell, which is used as an optical shutter, consists of a Kerr substance (usually a polar, organic liquid) placed in an insulating container with two electrodes. This is positioned between crossed linear polarizers whose transmission axes are at ±45 to the applied electric field. In order to obtain the half-wavelength retardation at which maximum contrast can be obtained, the cell needs to have a thickness (optical path length), d k/2 , ofFor example, a Kerr cell containing nitrobenzene, which is generally known to have a very large Kerr constant (K = 2.2 10 ±12 m V ±2 ), [1] requires a cell thickness of about 45 mm for application of an electric field, E, of strength E = 5 10 6 V m ±1 . Fast optical shutters can be used in flat-panel liquid-crystal displays, as these displays consist of arrays of small light shutters. However, Kerr shutters made of nitrobenzene are too thick to be used. Blue phases are liquid-crystalline phases that appear in a very small temperature range between the cholesteric phase (Ch) and the isotropic phase (Iso).[2±5] There are three types of blue phasesÐBPI, BPII, and BPIII. The BPI and BPII phases are characterized by cubic symmetry of the director field, with lattice constants that are comparable to the wavelength of visible light. [6,7] Since blue phases are optically isotropic in zero electric field due to their structural symmetry, surface treatment to obtain a specific molecular orientation, e.g., rubbing to obtain twisted alignment, is redundant. This is a great advantage for device fabrication, because the rubbing process introduces degradation of the display quality and increases manufacturing costs. Recently, we reported that the temperature range over which BPI exists, usually a few degrees Kelvin, was successfully extended to more than 100 K in the polymer±liquid crystal (blue phase) composite system, referred to as the ªpolymer-stabilized blue phaseº. [8,9] In this study, the Kerr effe...

The possibility of controlling light emission and propagation by exploiting periodic structures of dielectric media has attracted interest in the last decade. These photonic-bandgap materials, so-called photonic crystals, have generated considerable interest due to their wide applicability in optoelectronic and microwave devices.[1] In particular, emission control and lasing action in optically active photonic crystals can offer new applications for low-threshold lasers from small-size devices. [2][3][4] Currently an intensive effort is underway in molecular crystallography to develop photonic-bandgap materials with lattice parameters comparable to the wavelengths from visible to infrared light. This approach involves using liquid-crystalline materials that naturally form helical structures with a helical pitch in the optical-wavelength range.[5] The relevant optical property of the cholesteric phases of liquid crystals is the selective reflection of light over a range of wavelengths, that is, the photonic stop band. Previous studies have readily demonstrated that the lasing action of cholesteric liquid crystals can be attributed to the band-edge effect of the photonic stop band. These studies further explore mechanically, electrically, and chemically tunable photonic-stop-band responses [6][7][8] and a defect mode for a low-laser-threshold application. [9][10][11] Cholesteric liquid crystals can be regarded as one-dimensional photonic crystals, whereas the liquid-crystalline blue phases are three-dimensional cubic structures with lattice periods of several hundred nanometers, which give rise to selective Bragg reflections.[12] Therefore, probing light confinement in the blue phases and using them as novel molecularly assembled photonic crystals is of great interest. Although selective light reflections in the blue phases have already been studied for quite some time, [12][13][14] such three-dimensional extensions in molecular self-assembly are normally much more difficult to produce. A practical limitation of blue phases is their narrow temperature occupation (∼ 1-2°C) at the transition between the isotropic and cholesteric phases. The potential photonic application of the blue phases has been recently demonstrated by measuring the laser emission in three dimensions.[15]However, lasing action was still limited to a very narrow temperature range. Therefore, improving the temperature stability has been required for practical application of blue phases. [16,17] In this study, we describe the preparation of polymer-stabilized blue phases and the demonstration of laser emission attributed to the photonic effect of the blue-phase photonic crystal. The polymer network that forms in the blue phase leads to restriction of the deformation of the photonic crystal in a wide temperature range. We confirm the thermal stability of the polymer-stabilized blue phase by measuring laser emission over a wide range of temperature above 35°C. Pulsed excitation gives rise to laser emission with the low threshold excitation energy of a...

The local conformation of poly(methyl methacrylate) (PMMA) chains at the nitrogen (N 2 ) and water interfaces was studied by infrared-visible sum-frequency generation (SFG) spectroscopy. Although SFG spectra in the C-H region for PMMA at the N 2 interface have been hitherto reported, the peak assignments are not in accord with one another. Thus, we first made accurate assignments of SFG peaks using films, which had been well annealed at a temperature above the glass transition temperature for a long time, of three different deuterated PMMAs as well as normal protonated PMMA. At the N 2 interface, hydrophobic functional groups such as a methyl, ester methyl and methylene groups were present. While the a methyl group was oriented along the direction parallel to the interface, ester methyl and methylene groups were oriented normal to the interface. Quantitative discussion concerning the orientation of the functional groups of PMMA at the N 2 interface was aided by a model calculation.Once the PMMA film contacted water, the carbonyl groups of the PMMA side chains were oriented to the water phase to form hydrogen bonds with water molecules, resulting in the migration of ester methyl into the internal region of the film. Concurrently, the methylene groups became randomly oriented at the water interface and/or in part migrated into the internal region. Interestingly, the a methyl groups still existed at the water interface oriented along the parallel direction. The outermost region of PMMA in water can consist of hydrophilic and hydrophobic domains with sub-nanometre scale. Water molecules H-bond to themselves near the hydrophobic domains, leading to the formation of an ice-like structure of water molecules. However, water molecules adjacent to the hydrophilic domains H-bond with carbonyl groups.

Density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film spin-coated on a substrate in water, hexane, and methanol, which are "nonsolvents" for dPMMA, were examined along the direction normal to the interface by specular neutron reflectivity (NR). The interfaces of dPMMA with the liquids were diffuse in comparison with the pristine interface with air; the interfacial width with water was thicker than that with hexane. Interestingly, in water, the dPMMA film was composed of a swollen layer and the interior region, which also contained water, in addition to the diffused layer. The interface of dPMMA with hexane was sharper than that with water. Although there were slight indications of a swollen layer for the dPMMA in hexane, the solvent molecules did not penetrate significantly into the film. On the other hand, in methanol, the whole region of the dPMMA film was strikingly swollen. To conserve mass, the swelling of the film by the nonsolvents is accompanied by an increase in the film thickness. The change in the film thickness estimated by NR was in excellent accord with the results of direct observations using atomic force microscopy (AFM). The modulus of dPMMA in the vicinity of the interfaces with liquids was also examined on the basis of force-distance curves measured by AFM. The modulus decreased closer to the outermost region of the film. The extent to which the modulus decreased in the interfacial region was consistent with the amount of liquid sorbed into the film.

The segmental mobility of a typical amorphous polymer, polystyrene, at the interfaces with solid substrates was noninvasively examined by fluorescence lifetime measurements using evanescent wave excitation in conjunction with coarse-grained molecular dynamics simulation. The glass transition temperature (T(g)) was discernibly higher at the interface than in the internal bulk region. Measurements at different incident angles of excitation pulses revealed that T(g) became higher closer to the interface. The gradient became more marked with an increasing difference in the free energy at the interface between the polymer and solid substrate. The T(g) value at the interface decreased with decreasing molecular weight. However, the decrement for the interfacial T(g) was not as much as that for the bulk T(g), due to the restriction of chain end portions by the substrate. Finally, it was observed that when a film became thinner than 50 nm, the depressed mobility at the interface coupled with the enhanced mobility induced by the presence of the surface. The experimental and simulation results were in good accord with each other.