Pavel A. Kossyrev

Variable-wavelength switchable Bragg gratings formed in polymer-dispersed liquid crystals

We report a holographic polymer-dispersed liquid crystal cell whose reflection peak can be tuned as a function of applied voltage. Electro-optic results are presented which are in excellent agreement with our model based on coupled wave theory.

Expanded viewing-angle reflection from diffuse holographic-polymer dispersed liquid crystal films

A switchable diffuse reflective film with high color purity is demonstrated using holographic-polymer dispersed liquid crystals (HPDLC). By recording a diffuse hologram directly into the LC/polymer film, the diffuse mode HPDLC exhibit viewing angles an order of magnitude larger than the conventional mode. A simple phenomenological model based on coupled-wave theory is developed to describe our observations.

Virtual surfaces, director domains, and the Fréedericksz transition in polymer-stabilized nematic liquid crystals

The critical field of the Freedericksz transition and switching dynamics are investigated for polymer-stabilized nematic liquid crystals as a function of polymer concentration. A simple phenomenological model is proposed to describe the observed critical field and dynamic response time behaviors as a function of concentration. In this model, the polymer fibrils form director domains, which are bounded by “virtual surfaces” with a finite anchoring energy.

Improving the voltage response of holographically-formed polymer dispersed liquid crystals (H-PDLCs)

Abstract We report a significant improvement in the switching voltage of holographic PDLCs. This is achieved by doping the prepolymer with small amounts of organic surfactants. The effect of these dopants on other important H-PDLC performance parameters is also investigated. Possible explanations for the reduction in switching voltage are discussed in relation to simple phenomenological switching models.

Formation dynamics of diffraction gratings in reactive liquid crystals

Using in situ diffraction measurements of diffraction grating formation in a single component reactive mesogen system, the anisotropy in the diffusion constants is determined. The data are well explained by a diffusion model, which accounts for the density modulation due to shrinkage upon photopolymerization with interfering laser beams.

P-58: Diffuse H-PDLC Reflective Displays: An Enhanced Viewing-Angle Approach

We demonstrate a Holographic-Polymer Dispersed Liquid Crystal (H-PDLC) with an enhanced viewing-angle, formed by writing a diffuse hologram structure directly into our H-PDLC material. We model the diffuse H-PDLC reflectance by summing over the contributions of discrete grating domains of differing orientations. We use a normal distribution function to weight each orientation to describe the grating densities. SEM studies were performed to determine the morphologies and orientations of multiple gratings within the sample.

The Birefringent Texture of Nematic Liquid Crystals Confined to Capillary Tubes with Square Cross-Section

Abstract The structure of nematic liquid crystal director fields in supramicrometer capillary tubes with square cross-section is studied using polarizing optical microscopy. Frank elastic theory is used to determine theoretical director configurations for this geometry.

Yarn ball polymer microstructures: A structural transition phenomenon induced by an electric field

We report on an unusual polymer “yarn ball” microstructure that is created through a template-based synthetic process involving reactive mesogens. We present experimental results of a unique structural transition of the yarn ball when subjected to an electric field, and describe this transition with a modified elastic theory. We model the interactions of the mesogenic thread segments that comprise the yarn ball in terms of mean-field theory by introducing an intersegment potential.

P‐79: Model of Freedericksz Transition and Hysteresis Effect in Polymer Stabilized Nematic Liquid Crystal Configurations for Display Applications

The critical field of the Freedericksz transition and optical hysteresis is investigated for Polymer Stabilized Nematic Liquid Crystals as a function of polymer concentration. The results are described by a simple phenomenological model, which accounts for the change in polymer network morphology as the concentration of polymer is increased.

P‐108: Robust Polymer Stabilization for Cholesteric Liquid Crystal Reflective Displays

We have developed a robust way to stabilize cholesteric liquid crystal materials for reflective display applications. Using a photolithographic-type exposure process we enclose cholesteric liquid crystal in cylindrical containers to create a film that is extremely robust for flexible and conformable display applications. We discuss the influence of cylindrical containment on the cholesteric liquid crystal configuration and its influence on the electro-optic properties.