Photo-active liquid crystal nanodispersions

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The goal of the proposed research is to fabricate a novel type of polymer network liquid crystal, which will be highly light-sensitive. In these liquid crystal hybrids, light-sensitive nanoparticles, which are hold in place by polymer-chains, will reversibly and controllably photo-switch the liquid crystal director via photo-generated electric fields. Polymer network liquid crystals are candidates for the next generation of liquid crystal displays, microdisplays and liquid crystal-based spatial light modulators. In general, polymer network liquid crystals consist of a birefringent liquid crystal and up to 10% of in-situ generated, crosslinked polymer. This special type of liquid crystal is sought for because added polymer will greatly enhance the electro-optic response properties of neat liquid crystals. It is proposed to investigate nanoparticles with covalently bound photoactive surface agents, which will present an unprecedented feature in polymer liquid crystal research. These nanoparticles with surface grafted crosslinkers can be used as nanoparticulate photoinitiators in order to graft polymer to and fix them inside a growing polymer-network. Accordingly, nanoparticles will be incorporated in the polymer chains of polymer network liquid crystals to further push the response properties of these highly sensitive and responsive optical materials. Photo-active test devices are in the focus of the proposed project. Ferroelectric ceramics like iron-doped lithium niobate show the anomalous photovoltaic effect: If exposed with visible light of appropriate wavelength, a space charge separation is induced along their crystallographic c-axis, which generates high (several 10 kV) internal electric fields and evanescent electric fields at their surfaces. Accordingly, nanoparticles that consist of such materials can couple to the liquid crystal director via a unique mechanism. Use of such photo-active nanoparticles shows great prospects to push the response properties of polymer network LCs and lower their threshold of opto-optic switching: Liquid crystals posses dielectric anisotropy, which makes them an ideal tool to sense photo-generated electric fields and convert them into optic responses. The proposed research therefore has great prospects to lower the threshold of opto-optic responses in liquid crystals and explore the response properties of nanoparticles, which consist of materials that show the anomalous photovoltaic effect.