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Stratified phase-separated composite comprising a photo-polymerization dye Disclosure Number: IPCOM000008094D
Publication Date: 2002-May-17

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Stratified phase-separated composite comprising a photo-polymerization dye

      The invention relates to a stratified phase-separated composite, a method of manufacturing such a composite and photo-chemically reactive compositions for use in such a method.


      In Science vol.283 (1999) page 1903, Kumar et al (see also US 5,949, 508) disclose a phase-separated composite and a method of manufacturing such. The known composite is manufactured by providing, between a pair of opposed substrates, a layer of a photo-polymerizable monomer (prepolymer) dissolved in an organic liquid, in particular a liquid crystal. The organic liquid and monomer are selected such that the liquid is poorly

miscible with the photo-polymerized monomer. If so selected, phase-separation of the liquid and the photo-polymer takes place during photo-polymerization, a process known in the art as polymerization-induced phase separation (PIPS). In the composite of Kumar et al. the organic liquid is furthermore adapted to absorb the UV light used for photo-polymerizing the monomer. Therefore, according to Kumar et al, upon subjecting the layer to UV light, a light

intensity gradient is set up in the layer in directions normal to the layer, the highest intensity occurring at the side layer facing the UV light source. Since the rate at which photo- polymerization takes place scales with the intensity of UV light, photo-polymerization and therefore phase-separation preferentially takes place at the side of the layer facing the light source. As a result the phase-separation takes place in a stratified manner, producing

composite comprising a predominantly polymeric layer formed at the UV light source side and a predominantly liquid layer at the side facing away from the UV light source.

      The range of liquid crystals which can be suitably used to form a stratified- phase-separated composite is limited to those which absorb the radiation used to bring about phase-separation. However, for many applications, the use of other liquid crystals would be





desirable. In particular, liquid crystal used by Kumar, E7, a cyanobiphenyl LC is not suitable for use in AMLCD. A further disadvantage of the known composite may be that the phase- separation is not perfect. In particular, small amounts of LC material are still present in the polymeric layer. For many applications such inclusions of LC material may be undesirable.

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For example, the liquid crystal inclusions may give rise to spurious switching effects and if LC inclusions during the useful lifetime migrate to and merge with the liquid layer the properties, such as retardation or orientation, may be affected.


      It is an object of the invention, inter alia, to provide a stratified phase- separated composite which does not have these drawbacks. In particular, it is an object to extend the range of stratified-phase-separated composites by extending the range of fluids suitable for use in...