Temperature grafted silica dispersions

ODA and Sil-from-ODA shows distinct bend in the plots of temperature vs. retention factor (k) for triphenylene. No such remarkable temperature dependence is observed with ODS or any other phases. As shown by the in Fig. 7, Tc2 of Sil-to-ODA and Sil-from-ODA and that observed in DSC (in methanol dispersion) almost completely acceded with the temperature of the bending point. This strongly suggests that the typical temperature dependencies a property by polyoctadecylacrylate grafted silica occurs at the crystalline-to-isotropic phase transition temperature of the bonded phase. 

Systems such as Pseudomonas lipase dispersed inside Hyflo Supercell (a diatoma-ceous silica of pH 8.5-9) and SP 435 Novozym (Candida antarctica lipase grafted on an acrylic resin) are thermally stable and have optimum activity in the range 80-100 °C. They can therefore be used with conventional or microwave heating if the temperature is strictly controlled. 

Figure 7-6 shows the viscosity of thermoreversible dispersions (discussed in Section 7.2.4) of a 50-nm silica particles onto which octadecyl chains have been densely grafted in benzene at particle volume fractions 4> — 0.088-0.133, as a function of temperature T (Woutersen and de Kruif 1991). For T > 9 — 316 K, the viscosity relative to that of the solvent, rir = r /f]s, is independent of temperature, and its dependence on volume fraction 0 is exactly as expected for hard spherical particles without attractive interactions. As T is lowered below 9, however, the viscosity rises rapidly, because of the onset of attractive interactions. 

In traditional synthetic transformations, enzymes are normally used in aqueous or organic solvents at relatively low temperatures to preserve their activity. Therefore, it is not surprising that some of these reactions require long reaction times. In view of the newer developments that immobilize enzymes on solid supports [148], these reactions are now amenable to operation at higher temperature with adequate pH control. The application of MW irradiation has been investigated with Pseudomonas lipase dispersed in Hyflo Super Cell, which essentially consists of diato-maceous silica around pH 8.5-9.0 and commercially available SP 435 Novozym (Candida antarctica lipase grafted on an acrylic resin) [149]. 

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