Hollow particle crystalline colloidal arrays

Abstract

The invention includes a radiation diffracting member having a crystalline structure comprising an ordered periodic array of hollow particles. The radiation diffracting member also includes a matrix material in which the array of particles is received.

The invention claimed is: 
     
         1 . A radiation diffracting member having a crystalline structure and comprising:
 an ordered periodic array of hollow particles; and   a matrix material in which said array of particles is received.   
     
     
         2 . The radiation diffracting member of  claim 1 , wherein the crystalline structure defines a plurality of first planes through the hollow particles and a plurality of second planes spaced from the first planes, wherein the effective refractive index of the material in the second planes is at least 0.15 greater than the effective refractive index of the material in the first planes. 
     
     
         3 . The radiation diffracting member of  claim 1 , wherein the hollow particles contain air. 
     
     
         4 . The radiation diffracting member of  claim 1 , wherein the hollow particles comprise polystyrene, polymethyl methacrylate, acrylonitrile, divinyl benzene, polyurethane, acrylic polymer, alkyd polymer, polyester, siloxane-containing polymer, polysulfide, epoxy-containing polymer, and/or polymer derived from an epoxy-containing polymer. 
     
     
         5 . The radiation diffracting member of  claim 1 , wherein the hollow particles comprise a crosslinked polymer. 
     
     
         6 . The radiation diffracting member of  claim 5 , wherein the crosslinked polymer comprises polystyrene. 
     
     
         7 . The radiation diffracting member of  claim 1 , wherein the matrix material comprises styrene, divinyl benzene polyurethane, acrylic polymer, alkyd polymer, polyester, siloxane-containing polymer, polysulfide, epoxy-containing polymer, and/or polymer derived from an epoxy-containing polymer. 
     
     
         8 . The radiation diffracting member of  claim 1 , wherein said radiation diffracting member exhibits an image. 
     
     
         9 . The radiation diffracting member of  claim 8 , wherein the image comprises at least two regions that reflect radiation at two different wavelengths in said regions. 
     
     
         10 . The radiation diffracting member of  claim 9 , wherein said at least two regions comprise differing matrix materials. 
     
     
         11 . The radiation diffracting member of  claim 8 , wherein the image is detectable in the visible spectrum. 
     
     
         12 . A security device comprising:
 a substrate; and   the radiation diffracting member of  claim 1  positioned on a surface of the substrate.   
     
     
         13 . The security device of  claim 12 , wherein the substrate comprises a support member. 
     
     
         14 . The security device of  claim 13 , wherein the support member comprises a film. 
     
     
         15 . The security device of  claim 13 , wherein the support member comprises a microporous layer. 
     
     
         16 . The security device of  claim 13 , wherein the support member comprises an article. 
     
     
         17 . The security device of  claim 16 , wherein the article comprises a document of value or a credentials document. 
     
     
         18 . A method of making a radiation diffracting member comprising:
 receiving an ordered periodic array of hollow particles into a curable matrix composition; and   curing the matrix composition to fix the array of hollow particles within a matrix material.   
     
     
         19 . The method of  claim 18 , wherein the array of hollow particles is produced by applying a dispersion of similarly charged, monodispersed hollow particles onto a substrate and drying the dispersion, whereby the hollow particles pack into the ordered periodic array. 
     
     
         20 . The method of  claim 19 , further comprising producing an image in the radiation diffracting member. 
     
     
         21 . The method of  claim 20 , wherein the image is produced by receiving the ordered periodic array of particles into at least two different curable matrix compositions. 
     
     
         22 . The method of  claim 19 , wherein the image is produced by:
 receiving the ordered periodic array of particles into a first curable matrix composition;   curing a first portion of the first curable matrix composition to produce a partially cured assembly;   receiving the partially cured assembly within a second curable matrix composition; and   curing the second curable matrix composition.