Structured liquid crystal/polymer composites as photonic crystal switches and LCD innovations.

摘要

Mesoscale two- and three-dimensional lattices are formed in polymer-dispersed liquid crystal (PDLC) materials using one-step holographic fabrication. Discrete nematic liquid crystal (LC) domains are patterned within a rigid polymer binder (a multifunctional urethane acrylate) through an irradiance-driven diffusion and phase separation process, and are essentially low index-contrast photonic crystals whose index-modulation closely mimics the irradiance profile applied during formation. Electromagnetic fields are used to align the nematic configurations within the LC domains, allowing electrical control of the coherent scattering from these lattices.; Planar films of square, face-centered-cubic (FCC), hexagonal-close-packed (HCP), and simple-hexagonal lattices formed by four- and six-beam holography are characterized through scanning electron microscopy and various electro/thermo-optic techniques. Observed electro-optic effects relevant to photonic switching and liquid crystal display (LCD) applications include a strongly polarized Bragg reflection, an in-plane optical anisotropy, a wavelength-tunable stopband, and low-threshold switching. These holographic techniques enable the regular confinement of LC in spherical, ellipsoidal, and cylindrical cavities at lattice nodes with dimensions previously unattainable (50∼200 nm), allowing the physics of alignment and ordering at this scale to be fully understood.; In addition, a significant improvement in the dynamic response time of the In-Plane-Switching mode LCD is achieved through the introduction of a low-density, stabilizing polymer network that causes the nematic director to favor the zero-field orientation. The effect of polymer concentration on the electro-optical performance of the polymer-stabilized IPS mode cells is characterized through experiment, and a simple elastic-continuum model that treats the polymer network as an effective field is presented.