39.1: Invited Paper: Optically Isotropic Nano‐Structured Liquid Crystal Composites for Display Applications

Abstract

In this paper, we present the phase behavior and electro-optical Kerr effect of the optically isotropic liquid crystal composites, which require no surface treatment for device fabrication. Anomalously large Kerr constant, more than 10 -8 mV -2 and fast response, less than sub-milli-second were observed at a room temperature. IntroductionThe Kerr effect is a kind of quadratic electro-optic effect which is caused by an electric field induced-ordering of polar molecules and/or the second dipole hyperpolarizability of molecules in optically transparent and isotropic materials. It is well known that nematic liquid crystals exhibit an anomalously large electro-optic Kerr effect in an isotoropic phase just above the nematic-isotropic phase transition temperature, T NI . This is due to that the isotropic phase has the nematic-like short range ordering on a distance scale defined by a coherence length, ξ in that temperature region.Since such an anomalously large Kerr effect is associated with pretransitional fluctuation of the isotropic phase, the phenomenon inevitably disappears in a temperature range below T NI . The response time of the Kerr effect for nematic liquid crystals in an isotropic phase is much shorter (~1 μs) than that of realignment of directors in a nematic phase (10~100 ms). Considering practical applications in electro-optics, the Kerr effect in an isotropic phase of a nematic liquid crystal is attractive because of the short response time, but the problem of the steep temperature dependence of the Kerr constant should be overcome.It is an important challenge in electro-optic applications to develop a material which shows the anomalously large Kerr effect over a broad temperature range. In the case of usual nematics, ξ increases rapidly with decreasing temperature in the isotropic phase near T NI and diverges infinitely at T * as shown in Figure 1(a). If the rapid increase of ξ is suppressed within a finite size less than optical wavelength but larger than molecular dimension below T NI , an optically-isotropic state showing an anomalously large Kerr effect is expected to appear over a broad temperature range below T NI with low temperature dependence as shown in Figure 1(b).As the matter of course, the thermodynamic behavior of the optically-isotropic state in the nematic phase is intrinsically different from that of a genuine isotropic phase in the vicinity of T NI . One could draw, however, a phenomenological analogy between them if one focuses on only the orientational behavior of the local directors upon an application of an electric field. We have investigated the phase behavior and electro-optical properties of nano-structured liquid crystal composites including the polymer-stabilized blue phases [1][2][3][4][5][6][7]. This paper presents an anomalously large Kerr effect over a broad temperature range below T * with low temperature dependence for the polymer-network / chiral liquid crystals composites due to suppressing ξ below T* and their electrooptical properties.

From the discovery of the partially bilayer smectic A phase to blue phases in polar liquid crystals

“…The role of different defects in stabilisation of BPs was discussed recently by Fukuda and Žumer. [207] The interest in LC BPs has been rapidly intensified since Kikuchi et al [208][209][210][211] published the results of their work on stabilisation of BP by the polymer network. After the polymerisation of a mixture comprising a few per cent of mono-, di-and trifunctional monomers in the temperature range wherein a BP existed, the temperature range of BP was extended to hundred and more degrees below the clearing point.…”

Study and characterization of the smectic X* phase in binary mixtures of thermotropic double hydrogen bonded ferroelectric liquid crystals

“…To highlight a few varieties, molecular LCs, [11À15] polymer LCs,[16À20] ferroelectric LCs, [21] and nanolLCs [22,23] have been reported elsewhere. Single-bond,[24À26] double-bond, [27À30] and even multiplebonded [31,32] HBLCs are also synthesized and discussed.…”

High-transmittance polymer-stabilised blue-phase liquid crystal display with double-sided protrusion electrodes

“…Polymer-stabilised blue-phase liquid crystal display (PSBP-LCD) based on the Kerr effect [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] has the potential to be the next-generation display technology due to the following reasons: (1) its sub-millisecond gray-to-gray response time, [1,2] which is ten times faster than the present nematic LC displays; (2) it does not need alignment layer so that the fabrication process is greatly simplified; (3) it has a wide viewing angle -the voltage-off state is optically isotropic and the voltage-on state forms multi-domain structures [3,4] and (4) the transmittance is insensitive to the cell gap, so it can be used in large-screen LCDs. However, there are still many problems to be overcome, such as high operating voltage, low transmittance, large hysteresis and long-term stability.…”

“…[5][6][7][8][9] For instance, a polymer-stabilised blue-phase liquid crystal (PS-BPLC) material with a large Kerr constant (K∼12.68 nm/V 2 at λ = 550 nm) [10][11][12][13] has been recently developed. By optimising the in-plane switching (IPS) electrode width and gap, the driving voltage is reduced to ∼35 V. Wall-shaped [14] and protrusion electrodes [15] show very positive trend to lower the operating voltage to ∼10 V using PS-BPLC material with a large Kerr constant (12.68 nm/V 2 at λ = 550 nm), but the fabrication is complicated and the transmittance is greatly lowered.…”