Silica gels silanization process

Silica reinforced rubber, 22 703 Silica sheets, 22 383-385 Silica-silane system, 22 377-378 Silica sol-gel fiber processing, 23 80 Silica sols, 22 383, 473-474 applications of, 22 394 modification of, 22 393-394 preparation of, 22 392-393 properties of, 22 391-392 purification of, 22 393 Silica, solubility in steam, 23 212-213 Silica-supported activated manganese dioxide, 76 568... 

The incorporation of organofunctional groups on the silica surface may be effectuated during the synthesis of the silica material. The addition of organofunctional alkoxysilanes to the TEOS solution in the sol-gel process, produces functionalized silica gels. This procedure does not allow a careful control of the obtained surface morphology. Since the relative amounts of silane and TEOS is the only variable parameter, neither layer thickness, nor modification density can be precisely tuned. This results in an irreproducible functionalization of the surface. 

Metal-doped silica gels exhibit a wide range of optical properties which allow them to be used for optical and optoelectronic triplications. The preparation is done via the sol-gel process. Emission and absorption maxima as well as quantum yield can be adjusted by built-in functionalized silanes [2] or adsorbed semiconductor or metal colloids, respectively [3,4]. 

The products made by the above synthetic processes still have large numbers of residual silanols, which lead to poor peak shapes or irreversible adsorption, because chemically bonded groups on the silica gel surface have large, bulky molecular sizes and, after the bonding, the functionalized silane cannot react with the silanols around the bonded ligands. Because such alkyl-bonded phases are used for reversed-phase separations, especially for chromatography of polar molecules, any silanol groups that remain accessible to sol-... 

In an ideal surface structure, one out of every two silicon atoms has a silanol group which can be silanized by either mono-, di- or trichlorosilane. If the surface of the silica matrix is completely silanized by the bonded organic phase, the organic phase can prevent the corrosion of the silica gel by acid or basic solutions. If the silanol groups are not completely silanized by the first reaction, a second silanization process, known as end-capping, is required. The carbon content did not significantly increase in this endcapping process. 

Another widely used approach in this area is a sol-gel process. In order to create surface roughness after deposition of thin films, a secondary component is included in the sol-gel deposition process which can be removed later by dissolution in hot water or sublimation. The removal of the secondary components gives porous structures. Subsequent lluorinated silane coating can render these sol-gel processed films superhydrophobic [81-83]. Microporous structures can be created through phase separation of organic polymer solutions and then used as a template for sol-gel processing of porous silica substrates. Ruorosilane treatment of these substrates produces superhydrophobic surfaces [84]. 

The synthesis of the new MSSA is depicted in Scheme 1.2. The first step was the activation of the silica gel surface with HCI, then an excess of dimethylchlorosilane (DMCS) was used to accomplish the silanization process. Conversion of Si-Cl to Si-OH occurred when water was added to the solid product after 10 min of stirring at room temperature. After completion of all reactions, samples were dried in a nitrogen stream at 120°C for 24 h. Finally, the silanol groups were allowed to react with chlorosulfonic acid to yield the desired MSSA, without any side products as HCI gas evolved from the reaction vessel immediately. 

---