Crystalline colloidal array

Colloidal Crystalline Arrays Colloidal spheres of silica and of polymers can be made relatively monodisperse, with standard deviations of 4% of the mean diameter for silica and 1% for polymer latexes. The spheres pack as shown in Figure 11.22a from fluid dispersions into fee (sometimes hep or bcc) colloidal crystals (CC) by gravity, by membrane filtration, or by capillary forces at the surface of an evaporating dispersion (80-82). The crystalline order of the materials is strictly at the length scale of the packed colloidal particles the packing of the atoms and molecules within the silica and polymer particles is totally amorphous. The CCs diffract... 

Modification of the surfaces of coUoidal silica spheres with silane coupling agents enables transfer of the particles to nonpolar solvents. With 3-methacryloxypropyltri-methoxysilane bonded to the surface, the particles have been transferred from water to the polymerizable monomer, methyl acrylate. Electrostatic repulsion due to a low level of residual charge on the particle surfaces cause the dilute dispersions of particles to form a non-close packed colloidal crystalline array (CCA). Polymerization of the methyl acrylate with 200 nm diameter silica spheres in a CC fixes the positions of the spheres in a plastic film by the reactions shown in Figure 11.14. The difriaction... 

Figure 28 Preparation of the photonic structural sensors from colloidal crystalline arrays (CCAs) is performed by in situ copolymerization of the polymerizable receptor to yield polymerized colloidal crystalline arrays (PCCAs). A receptor-analyte recognition process can affect the changes in the CCA periodicity, and, following Bragg s law, the wavelengths of diffracted and transmitted light, which serve as a signal for the sensing event.

A solid emulsion is a suspension of a liquid or solid phase in a solid. For example, opals are solid emulsions formed when partly hydrated silica fills the interstices between close-packed microspheres of silica aggregates. Gelatin desserts are a type of solid emulsion called a gel, which is soft but holds its shape. Photographic emulsions are gels that also contain solid colloidal particles of light-sensitive materials such as silver bromide. Many liquid crystalline arrays can be considered colloids. Cell membranes form a two-dimensional colloidal structure (Fig. 8.44). 

Some colloids consist of well-defined molecules, with constant molecular weight and definite molecular shape, permitting them to be piled in a crystalline array. Crystalline proteins include egg albumin (MW 43000) and hemoglobin (MW 68000). Even viruses, such as, tobacco-mosaic virus, have been crystallized their molecular weights are in the neighborhood of 10,000,000 (bushy-stunt virus) to 2,000,-000,000 (vaccinia virus). 

Zhang, H., and Wirth, M.J. Electromigration of single molecules of DNA in a crystalline array of 300-nm silica colloids. Anal. Chem., 11,1237, 2005. 

Crystalline colloidal arrays (CCA) are mesoscopically periodic fluid materials which efficiently diffract light meeting the Bragg condtion (/-. These materials consist of arrays of colloidal particles which self assemble in solution into BCC or FCC crystalline arrays (7,5) (Figure 1) with lattice constants in the mesoscale size range (50 to 500 nm). Just as atomic crystals diffract x-rays that meet the Bragg condition, CCA diffract UV, visible, and near IR light (2-4) the diffraction phenomena resemble that of opals, which are close-packed arrays of monodisperse silica spheres (6). 

These crystalline colloidal arrays are complex fluids that consist of colloidal particles give Bragg diffraction pattern in ultraviolet, visible, or near-infrared light, depending on the spacings of the colloidal particle array. More recently, robust semisolid photonic crystal materials were formed by polymerizing a hydrogel network around the self-assembled crystalline colloidal arrays. 

Some colloids consist of well-defined molecules, with constant molecular weight and definite molecular shape, permitting them to be ordered in a crystalline array. Proteins have molecular masses ranging from about 10,000 to several hundred thousand. 

Asher S A, Holtz J, Liu L and Wu Z 1994 Self-assembly motif for creating submicron periodic materials. Polymerized crystalline colloidal arrays J. Am. Chem. Soc. 116 4997-8... 

Colloidal crystals can be grown by a templated approach too. Thus van Blaadcren and Wiltzius (1997) have shown that allowing colloidal spheres to deposit under gravity on to an array of suitably spaced artificial holes in a plate quickly generates a single crystalline layer of colloidal spheres, and a thick crystal will then grow on this basis. 

Bragg diffraction on crystalline colloidal arrays Photonic crystal material is composed of a crystalline colloidal array that diffracts light at wavelengths determined by the optical lattice spacing, which is affected by the presence of analyte 5,14,15... 

Asher, S. A., Crystalline colloidal array chemical sensing devices, In ACS PRF summer school on nanoparticle materials, June 6 18, 2004. Eastern Michigan University, Ypsilanti, MI, 2004... 

Pan G, Kesavamoorthy R, Asher SA. Nanosecond switchable polymerized crystalline colloidal array Bragg diffracting materials. Journal of the American Chemical Society 1998, 120, 6525-6530. 

Asher SA, Holtz JH. (1998) Polymerized crystalline colloidal array sensor methods, US5854078. 

Ordered macroporous materials (OMMs) are a new family of porous materials that can be synthesized by using colloidal microspheies as the template. - The most unique characteristics of OMMs are their uniformly sized macropores arranged at micrometer length scale in three dimensions. Colloidal microspheres (latex polymer or silica) can self assemble into ordered arrays (synthetic opals) with a three-dimensional crystalline structure. The interstices in the colloidal crystals are infiltrated with a precursor material such as metal alkoxide. Upon removal of the template, a skeleton of the infiltrated material with a three-dimensionally ordered macroporous structure (inverse opals) is obtained. Because of the 30 periodicity of the materials, these structures have been extensively studied for photonic applications. In this paper, the synthesis and characterization of highly ordered macroporous materials with various compositions and functionalities (silica, organosilica, titana, titanosilicate, alumina) are presented. The application potential of OMMS in adsorption/separation is analyzed and discussed. 

Asher, S., Peteu, S., Reese, C. et al.. Polymerized crystalline colloidal array chemical-sensing materials for detection of lead in body fluids. Anal. Bioanal. Chem., 373, 632, 2002. 

Foulger, S., Lattam, A., Jiang, P. et al., Optical and mechanical properties of polyfethylene glycol) methacrylate hydrogel encapsulated crystalline colloidal arrays, Langmuir, 17, 6023, 2001. 

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