Monodisperse colloidal spheres

A general three-step procedure for the formation of macroporous materials by colloidal crystal templating is illustrated in Figure 6. In the first step, monodispersed colloidal spheres assemble into ordered 3D or sometimes 2D arrays to serve as templates. Secondly, the voids of colloidal crystals are filled by precursors that subsequently solidify to form composites. Finally, the original spheres are removed, creating a solid framework with interconnected voids, which faithfully replicate the template arrays. 

Yin, Y. and Xia, Y., Self-assembly of monodispersed colloidal spheres into complex aggregates with well-defined sizes, shapes, and structures, A[Pg.578]

Furthermore, it has been known that monodisperse colloidal spheres have the ability to self-assemble into three-dimensional periodic colloidal crystals, only when their size distributions are less than 5 % [79]. That is a particular challenge to establish a new and facile synthesis strategy toward truly monodispersed carbon nanospheres [80]. Wang et al. [81] have established a new strategy of synthesis of highly uniform carbon nanospheres with precisely tailored sizes and high mono-dispersity on the basis of the benzoxazine chemistry. 

Li JG, Li X, Sun X, Ishigaki T (2008) Monodispersed colloidal spheres for uniform Y2O3 Eu red-phosphor particles and greatly enhanced luminescence by simultaneous Gd doping. JPhysChemC 112 11707... 

Monodispersed colloidal spheres can be self-assembled into ordered 2D arrays on solid supports or in thin films of liquids using a number of strategies [11-14]. 

Stdber W, Fink A and Bohn E 1968 Controlled growth of monodisperse silioa spheres in the mioron size range J. Colloid Interface Sol. 26 62-9... 

Stober, W., Fink, A., and Bohn, E.J. (1968) Controlled growth of monodisperse silica spheres in the micron size range. Colloid Interface Sci. 26, 62-69. 

It is difficult to obtain meaningful results on colloidal interactions unless the samples have low polydispersity. Studies of colloidal interactions between whole casein micelles can be affected by the polydispersity of native casein micelles. (Stothart,1987b). To circumvent the problem of polydispersity, the food system can be deposited on monodisperse silica spheres (Rouw and de Kruif,1989). 

Recent experimental studies (1-3), on systems of sterically stabilized colloidal particles that are dispersed in polymer solutions, have highlighted the role played by the free polymer molecules. These experiments are particularly relevant because the systems chosen are model dispersions in which the particles can be well approximated as monodisperse hard spheres. This simplifies the interpretation of the data and leads to a better understanding of the intcrparticle forces. DeHek and Vrij (1, 2) have added polystyrene molecules to sterically stabilized silica particles dispersed in cyclohexane and observed the separation of the mixtures into two phases—a silica-rich phase and a polystyrene-rich phase—when the concentration of the free polymer exceeds a certain limiting value. These experimental results indicate that the limiting polymer concentration decreases with increasing molecular weight of... 

F. Caruso uses monodisperse polymer spheres and their colloidal crystals only as templates to create hollow capsules or extended opal arrays with the layer-by-layer technique. Again this is a typical colloid chemistry tool which is unparalleled in low molecular weight organic chemistry, and hollow mesostruc-tures systems with astonishingly high complexity and chemical function can be generated. 

Another important method for photonic crystal fabrication employs colloidal particle self-assembly. A colloidal system consists of two separate phases a dispersed phase and a continuous phase (dispersion medium). The dispersed phase particles are small solid nanoparticles with a typical size of 1-1000 nanometers. Colloidal crystals are three-dimensional periodic lattices assembled from monodispersed spherical colloids. The opals are a natural example of colloidal photonic crystals that diffract light in the visible and near-infrared (IR) spectral regions due to periodic modulation of the refractive index between the ordered monodispersed silica spheres and the surrounding matrix. 

Macroporous VPO Phases. - The macroscale templating of bulk mixed metal oxide phases in the presence of colloidal sphere arrays typically consists of three steps shown in Figure 18. First, the interstitial voids of the monodisperse sphere arrays are filled with metal oxide precursors. In the second step, the precursors condense and form a solid framework around the spheres. Finally, the spheres are removed by either calcination or solvent extraction leading to the formation of 3D ordered macroporous structures [137]. 

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