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Stratified phase-separated composite having cross-linked polymeric layer

IP.com Disclosure Number: IPCOM000008091D
Publication Date: 2002-May-17
Document File: 23 page(s) / 70K

Publishing Venue

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Abstract

NL010920

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This is the abbreviated version, containing approximately 6% of the total text.

Page 1 of 23

PHNL010920WO

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Stratified phase-separated composite having cross-linked polymeric layer

The invention relates to a stratified phase-separated composite and a method of manufacturing such a composite.

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 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 a 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.

      A disadvantage of the known composite is that the stratification is not complete. In particular, the polymeric layer comprises small amounts of liquid crystal material. For many applications such inclusions of LC material may be undesirable. For example, the liquid crystal present in the polymeric layer may give rise to spurious switching effects and/or during the useful lifetime of the composite liquid crystal material may migrate

to and merge with the liquid layer so as to affect the properties of the liquid crystal layer, such as its retardation or orientation.


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PHNL010920WO

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      It is an object of the invention, inter alia, to provide a stratified phase- separated composite which does not have these drawbacks or at least to a lesser extent. In particular, it is an object to provide a stratified-phase-separated composite which is well- stratified. In particular, the number of liquid molecules present in the polymeric layer (regardless the form in which such liquid molecules are present, ie dispersed as droplets or

dissolved on a molecular scale) is to be low.

      In accordance with the invention, these objectives are achieved by a stratified phase-separated composite comprising a crosslinked polymeric layer and a liquid layer, the c...