Polymer filled nematics : a new class of light scattering electro-optical devices

M.C.W. Boxtel, van, D.J. Broer, C.W.M. Bastiaansen

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    Abstract

    Electro-optical switches based on low molecular weight liquid crystals are increasingly used in a large range of flat panel display applications. Here, a new display principle is presented based on (sub)micron-sized highly crosslinked polymer particles dispersed in a continuous, low molecular weight liquid crystal, referred to as "Polymer Filled Nematics (PFN's)". These electro-optical devices can be electrically switched from a light scattering to a transparent state. In general, the optical and electro-optical properties of LCD's based on two-phase mixtures strongly depend on, for instance, the degree of phase separation between the two phases, the interfacial interaction and on the shape and dimensions of the two phases. Conventional Polymer Dispersed Liquid Crystal (PDLC) blends, which consist of liquid crystal droplets dispersed in a continuous polymer phase, are usually prepared via controlled phase separation processes. However, the phase separation is never complete and control over the final morphology of the PDLC blend is difficult. In PFN's the dispersed polymeric phase is produced prior to the preparation of the blend, via free radical dispersion polymerisation in organic medium. In this way it becomes possible to tune the morphology of the final polymer/LC blend with respect to chemical and physical properties, interfaces and dimensions of both constituent phases. Moreover, it seems that, via this novel processing route, the production of completely phase separated polymer/LC blends is enabled, which further promotes the accurate control of both the structure and the properties of electro-optical cells produced from these materials. Rather surprisingly, it was also found that, due to the rheological properties of the blends, long term stable, thin layers of these PFN blends can be simply produced by conventional coating processes. Efforts were directed towards characterisation of the polymerisation process and towards derivation of structure-property relationships for the PFN blends serving as model systems.
    Original languageEnglish
    Title of host publicationPolymer Processing Society : annual meeting, 15th, 's-Hertogenbosch, The Netherlands, May 31 - June 4, 1999 : proceedings
    EditorsP.D. Anderson, P.G.M. Kruit
    Place of Publication's Hertogenbosch, The Netherlands
    Publication statusPublished - 1999

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