Silica microparticle/microsphere

Silica-based microspheres are typically between 5 and 200 j,m in diameter, have wall thicknesses of 0.5-20 pm and can be filled with up to 100 M Pa of H2. The spheres are formed by melting spray-dried microparticles in free fall and the evolving gases... 

Membrane and microfiuidic devices have also been adopted for the precision manufacture of solids from double-emulsion templates. To date, several different types of particles have been successfully produced by incorporating use of various membrane and microfiuidic devices in processes of polymerization, gel formation, crystallization, and molecular or particle self-assembly. Membrane emulsification is more suited to the fabrication of less sophisticated particulates, such as solid lipid micro-Znanoparticles, gel microbeads, coherent polymeric microspheres, and inorganic particles such as silica microparticles. Microfiuidic devices allow more sophisticated particle designs to be created, such as colloidosomes, polymerosomes, 3D colloidal assemblies, asymmetric vesicles, core-shell polymer particles, and bichromal particles. 

It is also relevant that silica microspheres being readily biodegradable and of no toxicity, they will not contaminate the environment as the cmrent commercial trend in their use continues, production of increasing quantities of sol-gel-derived silica-based fimctional materials will inevitably result in the introduction of granules and microparticles made of amorphous silica (or organosilica) in environmental matrices and in the biosphere (Table 18.2). 

If in a hydrophilic—hydrophobic silicas—water mixture (prepared at >10,000 rpm), the inner layer is composed of hydrophobic silica and the outer layer is of hydrophilic silica that air bubbles can be entrapped in the microspheres. The bulk density of this fresh gel-like mixture can be relatively low, 0.5-0.6 g/cm due to entrapped air (Mironyuk et al. 1994,1999). In the case of the opposite structure of the composition, water is located inside microparticles with the hydrophobic outer shell that give the dry water material mentioned earlier. In the dry water materials, instead of hydrophilic silica, starch or other superhydrophilic polymers or other hydrophilic compounds can be used to provide stronger and longer retention of water inside microparticles. 

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