Monodisperse spherical silica dispersions

Yoldas B.E. Alumina sol preparation from alkoxides. Am. Ceram. Soc. Bull. 1975 54 289-290 Yoshida M., Lai M., Kumar N.D., Prasad P.N. Ti02 nano-particle-dispersed polyimide composite optical waveguide materials through reverse micelles. J. Mater. Sd. 1997 32 4047-4051 Yoshizawa K., Sugoh Y., Ochi Y. Controlled growth of monodispersed spherical silica by a new synthetic process. In Science ofCeramics Vol. 14, D. Taylor, ed. Stoke-on-Trent, UK The Institute of Ceramics, 1988... 

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. 

After an aqueous dispersion of monodispersed spherical colloids was injected into the cell, a positive pressure was applied through the glass tube to force the solvent (water) to flow through the channels. The beads were accumulated at the bottom of the cell, and crystallized into a three-dimensional opaline lattice under continuous sonication. So far, we have successfully applied this approach to assemble monodispersed colloids (both polystyrene beads and silica spheres) into ccp lattices over areas of several square centimeters. This method is relatively fast opaline lattices of a few square centimeters in area could be routinely obtained within several days. This method is also remarkable for its flexibility it could be directly employed to crystallize spherical colloids of various materials with diameters between 200 nm and 10 pm into three-dimensional opaline lattices. In addition, this procedure could be easily modified to crystalhze spherical colloids with diameters as small as 50 nm. ... 

Dispersed colloidal silica particles of various sizes and colloidal silica crystals (opals) " have been used as templates of porous carbons, with spherical pores having narrow pore size distributions (PSDs). By coating monodisperse colloidal silica particles or crystals with a suitable carbon precursor, followed by carbonization and etching of the sUica, porous carbon particles can be obtained. The diameters of the mesopores are determined by the size of the silica particles. Because... 

A. van Blaaderen and A. Vrij Synthesis and characterization of colloid dispersions of fluorescent, monodispersed silica spheres, Langmuir, 8 (1992) 2921-2931 J.D. Wells, L.K. Koopal, and A. de Keizer Monodisperse, nonporous, spherical silica particles, Colloids Surf. A Physicochem. Eng. Asp., 166 (2000) 171-176 Howard A. Ketelson, Robert Pelton, and Michael A. Brook Surface and colloidal properties of hydrosilane-modifledStOber silica. Colloids Surf. A Physicochem. Eng. Asp., 132 (1998) 229-239... 

Valentin C., Munoz M.C., Alarcdn J. Synthesis and characterization of vanadium-containing ZrSi04 solid solutions from gels. J. Sol-Gel Sci. Technol. 1999 15 221-230 Van Helden A.K., Jansen J.W., Vrij A. Preparation and characterization of spherical monodisperse silica dispersions in nonaqueous solvents. J. Colloid Interf. Sci. 1981 81 354-368 Woodhead J.L. Sol-gel processes to ceramic particles using inorganic precursors. J. Mater. Educ. 1984 6 887-925... 

Let us assume that the particles are randomly distributed across drops irrespective of drop volume, so that even in antifoam emulsion the volume size distribution of drops is the same irrespective of the presence or absence of particles. The probability of obtaining particle-free drops is then equal to the total volume fraction of such drops (so that go = o)- I which case, we calculate from Equation 6.4 that N/M 0.46 if volume fractions of particle-free drops are to match the values of 0.63 indicated by experimental observation of the silica content of the agglomerates in deactivated antifoam dispersions. Since N/M < 1, this means that such high volume fractions are predicted to occur only in the case of dilute systems where the number of drops exceeds the number of particles. Obviously, this situation could be achieved as antifoam is dispersed where the number of drops increases, as a result of splitting, because the number of particles then remains constant so the ratio MM must decline. Here we note that if both particles and drops are spherical and monodisperse and the overall volume fraction of the particles is small, then... 

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