Hollow silica microspheres

Fowler, C.E., Khushalani, D. and Mann, S. (2001) Facile synthesis of hollow silica microspheres. Journal of Materials Chemistry, 11, 1968—1971. 

Alkoxysilanes can also act as oil droplets. Hollow silica microspheres of diameters 0.3-65 pm were prepared in a CTAB-stabilized emulsion system consisting of water and the mfacture of TEOS and aminopropyltriethoxysilane (10 mol%) as the oil phase [18]. Organo-functionalization of the microspheres was achieved by replacing TEOS with organotriethoxysilane, and encapsulation of TEOS-soluble additives within the silica shdls was demonstrated by incorporation into the ethoxysilane droplets. 

Synthesis of stable hollow silica microspheres with mesoporous shell in nonionic W/O emulsion. Chem. Commun., 2434-2435. 

The silica microspheres provide some diversity but not enough for many complex discrimination tasks. To introduce more sensor variety, hollow polymeric microspheres have been fabricated8. The preparation of these hollow microspheres involves coating silica microspheres by living radical polymerization, using the surface as the initiation site. Once the polymer layer forms on the silica microbead surface, the silica core is removed by chemical etching. These hollow spheres can be derivatized with the dye of interest. The main advantage of these polymer microspheres is the variety of monomers that can be employed in their fabrication to produce sensors with many different surface functionalities and polymer compositions. 

Mandal T. K., Fleming M. S., Walt D. R., Production of hollow polymeric microspheres by surface-confined living radical polymerization on silica templates, Chem. Mater. 2000 12 3481-7. 

The HGMs produced were heat treated at 620 °C for 18 hours before they were leached in 4 molar HC1 solutions at 80 "C for 4 hours. Heat treatment produced phase separation which resulted in a silica-rich phase and a more soluble and interconnected, sodium borate phase. Leaching removed the soluble sodium borate phase of the glass and created porosity through the microsphere walls. The porous wall, hollow glass microspheres, sank to the bottom of the solution. These sinkers were collected, water washed and dried at 100 °C overnight. 

Syntactic foams manufactured from hollow glass or silica microspheres and an epoxide, phenolic or other matrix resin represent a class of lightweight structural materials used for buoyancy purposes, insulation and packaging. The effect of silanes on the mechanical properties of syntactic foams at a nominal density of 0.35 g/cm3 is shown in Tables 14-16. The Proportional Limit is defined as the greatest stress which the foam is capable of sustaining without any deviation from proportionality of stress to strain (Hooke s Law). 

Silica microspheres ( 3 /tm) with initiating moiety (S-8) induced the copper-catalyzed radical polymerization of benzyl methacrylate to form polymer layers on the surface.459 The thickness of polymer shell can be increased to 550—600 nm, where the Mn and MWDs of the arm polymers were 26500 and 1.26, respectively. Removal of the core silica by chemical etching gave uniform hollow polymer microspheres. 

Although phosphates have usually been absent from most reported products, fired hollow ceramic spheroids made from AlP04/Na2Si03/Kaolin/Al203 compositions have been patented [66]. Microcellular siliceous materials have been synthesised and phosphates may prove to have important application in this field. Very-low-density (-0.003 g/cc) silica aerogels may have their AIPO4 counterparts. Phosphate-bonded silica microspheres are promising materials [67,68]. 

Katagiri et al. reported the preparation of hollow Ti02 microspheres by layer-by-layer assembly of TALH and positively charged polyelectrolytes on colloidal silica templates [65]. Hydrothermal treatment of the Ti02-coated particles led to... 

Li, H., Ha, C-S., and Kim, I. (2008) Facile fribrication of hollow silica and titania microspheres using plasma-treated polystyrene spheres as sacrificial templates. Langmuir, 24,10552-10556. 

The materials employed for making hollow microspheres include inorganic materials such as glass and silica, and polymeric materials such as epoxy resin, unsaturated polyester resin, silicone resin, phenolics, polyvinyl alcohol, polyvinyl chloride, polyjM-opylene and polystyrene, among others, commercial jx oducts available are glass, silica, phenolics, epoxy resin, silicones, etc. Table 36 shows low-density hollow spheres. Table 37 shows physical properties of glass microspheres, and Table 38 shows comparison of some fillers on the physical properties of resulting foams (10). 

Inexpensive, finely ground minerals like barium sulfate (barytes), dolomite, limestone (whiting), clays, and silica are widely used to provide bulk and reduce the cost of friction material formulations. These materials also act as friction modifiers and alter the performance of the end product. Other less commonly used fillers are hollow and solid organic and inorganic microspheres and fly ash. 

Fowler CE, Khushalani D, Mann S (2001) Interfacial synthesis of hollow microspheres of mesostructured silica. Chem Commun (19) 2028-2029... 

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