Silica films coating solutions

Solid phase micro extraction (SPME) is a techniques in which a silica fiber coated with a thin film of polymer is brought into contact with an aqueous matrix where the organics in solution partition onto the fiber. The fiber is subsequently placed into the injector of a GC where the heat causes the release of analyte onto the column. This has been applied to endosulfan (a- and (3-) and endosulfan sulfate in water with limits of detection of less than 0.3 pg/L reported (Magdic and Pawliszyn 1996). 

By spin coating the mixture containing the prehydrolyzed TMOS and a 0.2 M aqueous solution of C18TAC (pH=2, at the molar ratio of TMOS C18TAC=9.2.T), a transparent thin film formed on the substrate. The X-ray diffraction pattern of the film (Figure 1a) showed a sharp diffraction peak with the d value of 4.6 nm, which accompanied the 2nd order reflection. In order to remove the surfactants from the substrate to obtain porous silica films, the as coated film of the silica-surfactant mesostructured material was calcined in air at 450 °C. Sharp diffraction peak was observed in the XRD pattern of the calcined film... 

The stationary phase for LLC is usually silica coated with a thin film of liquid. The latter is the stationary phase itself. The coating is performed by treatment of the silica by a solution of this liquid in a suitable solvent and subsequent displacement of the solvent by mobile phase. NP-LLC occurs when the stationary phase is polar contrary to RP-LLC where the stationary phase is nonpolar. 

The precipitation of higher-ratio insoluble silicates from hot solution may be used to deposit siliceous coatings on hydrophilic surfaces. Sams (122) discloses that silica-rich coatings for optical or protective effects are deposited on surfaces such as glass from 2 1 ratio lithium silicate solution when the surface is immersed in the solution as it is heated to 95 C. Even after 10 sec, there is formed a colored film showing light interference, which must be of the order of 0.3 microns in thickness. Solutions with ratios from 1.3 1 to 10.7 1 may be used. 

Some discrimination between different alcohols is evident (Innocenzi, 2001b). Spin coated silica films with a cubic structure have also been incorporated into a surface photovoltage gas sensor (Yamada, 2002). Dip coated mesoporous thin films on a macroporous or mesoporous support have been prepared for separation membrane applications (Kim, 2002, 2003). Spin coating has also been used to deposit CieTABr templated films where the silicate walls were composed of nanosized zeolite MFI crystals co-deposited with the TEOS solution (Petkov, 2003).The continuous film contained a wormlike mesostructure and zeolite nanocrystals aligned with the a-axis perpendicular to the substrate, however the surface roughness of the film was increased. 

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