Silica sphere

A detailed study by Grieser and co-workers [169] of the forces between a gold-coated colloidal silica sphere and a gold surface reveals the preferential adsorption of citrate ions over chloride to alter the electrostatic interaction. 

Figure C2.6.1. SEM image of silica spheres of radius a = 15 nm and polydispersity a < 0.01 (courtesy of Professor A van Blaaderen)...

Advances have been made in directly measuring the forces between two surfaces using freshly cleaved mica surfaces mounted on supports (15), and silica spheres in place of the sharp tip of an atomic force microscopy probe (16). These measurements can be directly related to theoretical models of surface forces. 

High-pressure pumps operating at up to 6000 psi are required to force solvent through a tightly packed HPLC column, and electronic detectors are used to monitor the appearance of material eluting from the column. Alternatively, the column can be interfaced to a mass spectrometer to determine the mass spectrum of every substance as it elutes. Figure 12.18 shows the results of HPLC analysis of a mixture of 10 fat-soluble vitamins on 5 jam silica spheres with acetonitrile as solvent. 

The sacrificial core approach entails depositing a coating on the surface of particles by either the controlled surface precipitation of inorganic molecular precursors from solution or by direct surface reactions [2,3,5,6,8,9,33-35,38], followed by removal of the core by thermal or chemical means. Using this approach, micron-size hollow capsules of yttrium compounds [2], silica spheres [38], and monodisperse hollow silica nanoparticles [3,35] have been generated. 

Pol VG, Gedanken A, Calderon-Moreno J (2003) Deposition of gold nanoparticles on silica spheres a sonochemical approach. Chem Mater 15 1111-1118... 

Pol VG, Srivastava DN, Palchik O, Palchik V, Slifkin MA, Weiss AM, Gedanken A (2000) Sonochemical deposition of silver nanoparticles on silica spheres. Langmuir 18(8) 3352-3357... 

Generalized fabrication of multifunctional nanoparticle assemblies on silica spheres. Angewandte Chemie International Edition, 45 (29), 4789—4793. 

Stober, W Fink, A. and Bohn, E. (1968) Controlled growth of monodispersed silica spheres in the micron size range. Journal of... 

Encapsulation via the layer-by-layer assembly of multilayered polyelectrolyte (PE) or PE/nanoparticle nanocomposite thin shells of catalase in bimodal mesoporous silica spheres is also described by Wang and Caruso [198]. The use of a bimodal mesoporous structure allows faster immobilization rates and greater enzyme immobilization capacity (20-40 wt%) in comparison with a monomodal structure. The activity of the encapsulated catalase was retained (70 % after 25 successive batch reactions) and its stability enhanced. 

Darbandi, M., and Nann, T. (2005) Single quantum dots in silica spheres by microemulsion synthesis. 

Verhaegh, N.A.M., and van Blaaderen, A. (1994) Dispersions of rhodamine-labeled silica spheres synthesis, characterization, and fluorescence confocal scanning laser microscopy. Langmuir 10, 1427-1438. 

Stober A process for making metal oxides in the form of small spheres of uniform diameter by the controlled hydrolysis of metal alkoxides. First used in 1968 to make silica spheres from alkyl silicates. The products can be used to make high quality oxide ceramics. See also Sol-Gel. 

Figure 5.33 Electron micrographs of nanoparticle helices inside tubules of DC8,nPC+ 2% DCgj9PEOH after sequential absorption of charged polymers followed by treatment with 45-nm silica spheres. Reprinted with permission from Ref. 141. Copyright 2000 by the American Chemical Society.

Yamada, Y. Nakamura, T. Ishi, M. Yano, K., Reversible control of light reflection of a colloidal crystal film fabricated from monodisperse mesoporous silica spheres, Langmuir. 2006, 22, 2444 2446... 

The fiber-taper coupling scheme was applied to liquid-immersed water-droplet microsphere resonators by Hossein-Zadeh and Vahala35. The water droplets of diameter 0.5 1 mm were generated by a syringe and immersed in a low refractive immiscible cladding liquid - an index matching oil with a refractive index of 1.3, and trapped on a silica sphere which was fixed to the bottom of a liquid container... 

Figure 7.1 Transmission electron micrographs of rhodium particles supported on silica spheres (from Datye and Long [7]). 

Figure 3.6 Silica spheres with monodisperse particle size are expensive analytical gels of top performance. Silica spheres with determined particle size ranges are ideally suited for preparative chromatography. (Photo courtesy of SiliCycle.)...

Fig. 12.7 (a) Fabrication schematic of a graphene-encapsulated metal oxide, (b) Zeta potentials of APS-modified silica ( ) and graphene oxide ( ) in aqueous solutions with various pH values, (c) and (d) typical SEM, and (e) transmission electron microscopy (TEM) images of graphene-encapsulated silica spheres. Reprinted with permission from [87]. Copyright 2010, John Wiley Sons, Inc. 

The porous membrane templates described above do exhibit three-dimensionality, but with limited interconnectedness between the discrete tubelike structures. Porous structures with more integrated pore—solid architectures can be designed using templates assembled from discrete solid objects or su-pramolecular structures. One class of such structures are three-dimensionally ordered macroporous (or 3-DOM) solids, which are a class of inverse opal structures. The design of 3-DOM structures is based on the initial formation of a colloidal crystal composed of monodisperse polymer or silica spheres assembled in a close-packed arrangement. The interconnected void spaces of the template, 26 vol % for a face-centered-cubic array, are subsequently infiltrated with the desired material. 

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