Trimethylsilyl aerosil

The analysis of NMR spectra of high resolution in solid phase as well as the results of mass-spectrometry investigation of water and methanol desorption from trimethylsilylated aerosil surface with no OH-groups [64,115] testify a nonhydroxylic nature of the sites of adsorption of small water amounts. A correspondence has been fixed of three characteristic regions of the sorbed water and methanol elimination with desorption maxima related to probable destruction of hydrogen-bonded (low-temperature maximum) and coordinate adsorption complexes of various structure (high-temperature maximum) by the help of desorption-field mass-spectrometry [116,117]. 

On the other hand, trimethylsilyl aerosil, though unwettable by water is well phygocytosed (Strecker 1956). But it is just a matter of time un-... 

However, as was shown by Stbber (219), the silanol groups on a silica surface do not react quantitatively. Apparently, the trimethylsilyl group is too large and will block access to neighboring silanol groups. About 40% of the silanol groups on Aerosil formed trimethylsiloxane... 

The influence of chemical modification of silica surfaces by treatment with trimethylsilyl chloride was studied also by A. V. Kiselev and collaborators (221), Babkin et al. (222), and Babkin and Kiselev (223). They reported that no change occurred in (CHglaSiCl-treated Aerosil even after storing for months underwater (221). Lowen and Broge (224) investigated the influence on the heat of wetting and methyl red adsorption. 

Furthermore, Stober (219), and Stober e< al. (225) found that the rate of dissolution of Aerosil (specific surface area = ca. 150 m /gm) had diminished considerably after treatment with trimethylsilyl chloride. On agitating with aqueous solutions buffered to pH 6.9, no silicic acid was found at all in the solution before 18 hours. After 8 weeks, one-third of the trimethylsiloxane groups were still present on the surface. No difference in the rate of dissolution as compared with untreated Aerosil was observed in slightly alkaline medium. 

Stark and co-workers35 used radiochemical tracer methods to model the sorption of HMDS on silica. They confirmed a 1 1 stoichiometry of silanols reacted vs. trimethylsilyls formed. Zettlemoyer and Hsing36 studied the interaction of HMDS with silica in the NIR region. They contested the statement of Hair37 that HMDS reacts solely with free hydroxyl groups, and proved that intraglobular hydroxyls on aerosil... 

Two types of Aerosil with different surface activity have been studied hydrophilic and hydrophobic Aerosil. Hydrophilic Aerosil contains on its siirface hydroxyl groups which are the sites of adsorption. The surface groups of hydrophilic Aerosil are able to interact with the PDMS chain both through permanent dipoles in the partially ionic siloxane bond via permanent dipole-dipole interactions and through even weaker van der Waals forces. In contrast to hydrophilic Aerosil, non-polar trimethylsilyl groups on the surface of hydrophobic Aerosil effectively decrease the dipole-dipole interaction and mainly weak van der Waals forces are formed between methyl groups of PDMS and trimethylsilyl surface groups of Aerosil. 

Sithean VWR Int l. http //www.vwrsp.com Trade Name Synonyms Dynasylan CH7280 [Degussa/Aerosil Silanes http //www.degussa.de]-, H7280 [United Chem. Tech, http //www.unitedchem.com] Hexamethyidisilazane CAS 999-97-3 EINECS/ELINCS 213-668-5 Synonyms Bis (trimethylsilyl) amine Di (trimethylsilyl) amine Hexamethylsilazane HMDS GAP... 

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