Nanometer-sized silica

Synthesis of Nanometer-Sized Silica by Controlled Hydrolysis in Reverse Micellar Systems... 

Garda et al. [204] prepared composites of nylon-6 polymer with nanometer-sized silica (Si02) filler by compression molding. The addition of 2wt% Si02 resulted in a friction reduction from 0.5 to 0.18 when compared with neat nylon-6. This low silica loading led to a reduction in wear rate by a factor of 140, whereas the influence of higher silica loadings was less pronounced. 

Silica nanoparticles have been widely used as fillers in the manufacture of coatings [103], rubber [104], plastics [105], binders [106], functional fibers [107], etc. In recent years, the preparation of organic-inorganic hybrid materials composed of polymers and functionalized silica nanoparticles has been widely investigated. The combination of organic polymer components with nanometer-sized silica fillers in a single material has extraordinary significance for the development of hybrid materials with unique properties. 

Physical adsorption and covalent attachment of both native and reconibinant OPH onto various supports such as nylon membranes, porous glass and nanometer size silica beads have been enqiloyed (3,21,22).. Unfortunately, physical adsorption offers poor and nonspecific binding, vdiile coval modifications to OPH often results in reduction of enzyme activity and kinetic properties (22,23). In addition to reducing catalytic activity, there is no controlled orientation of the immobilized enzymes, leading to inaccessibility of the substrate to the enzyme active site. In the case of covalent bondii, the immobilization support is not reusable since the formed covalent bond is irreversible. In addition, the tedious and costly protocol for purification of OPH limits its use in large-scale enzymatic degradation. 

Exceedingly monodispersed nanometer-sized silica particles can also be produced by a so-called microemulsion technique, which employs essentially the same chemicals as the Stober process. However, the presence of a surfactant and the oil-phase provide means of creating small (nanometer sized) water droplets (microemulsion), within which the particles are formed. These droplets can be seen as size-limiting reaction vessels, producing very small but rather uniform nanoparticles. Since this technique is not limited to sUica, it has been applied to the synthesis of many different nanopowders. 

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