New electro-optical applications of LCs: from beam steering devices and tunable lenses to negative refraction and field-induced dynamics of colloids

Oleg Pishnyak, ,

Kent State University

Modern electro-optical applications require low cost, fast operation speed and low weight. Liquid crystals (LCs) are providing all these features, but there are problems still unsolved and there are phenomena still unexplored. In the Dissertation we explored new approaches for electro-optical applications of LCs. We described new designs of LC-based devices as well as shed some light on relatively new phenomena, such as negative refraction and electrically-controlled dynamics of colloidal particles in LCs. The main results obtained in this work are as follows: 1) Electrically tunable amphoteric (negative and positive) refraction was observed in nematic LC. The very existence of negative refraction in LC has been proven. Applications of the demonstrated phenomenon may include, e.g., beam steering devices. 2) Applicability of SmA materials for birefringent prisms useful in digital beam steerers and dual-frequency nematic for fast achromatic polarization rotator based on 45-degree twisted nematic cells has been demonstrated. 3) Applicability of dual-frequency nematic for LC-based lens with a hole-patterned electrode structure, which focal length can be tuned by the electric field from negative to positive values, has been demonstrated. Such a design can be used to achieve fast optical communication between multiple channels, for example, in microlens arrays, in beam steering or scanning devices or for fast non-mechanical zooming in miniature cameras. 4) Behavior of colloidal particles dispersed in a nematic LC and surrounded by hyperbolic-type defects has been explored. We observed a number of interesting effects, such as levitation of particles in the bulk, selective movement of particles toward the opposite substrates according to the orientation of satellite defects and bidirectional motion controlled by electrically-induced backflow. The observed phenomena open the possibility for electrically-driven particles manipulation in LCs. This may result in many practical applications, including particles sorting, electrically-driven LC microfluidic devices, development of LC-based electrophoretic displays, etc. The studied LC-based colloidal dispersions also offer an excellent model system to study viscoelastic properties of complex fluids, Brownian motion, interparticle interactions, hydrodynamics, pedestrian and traffic behavior, aggregation and jamming phenomena, etc. These studies are currently in progress.

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