Silica hydrophobised

In an earlier study in this laboratory (8) it had been shown that PS does not adsorb onto hydrophobised (methylated) silica from DMF. It is clear from the present results, however, (sample S12/PS 19, table III) that PS does adsorb onto silica particles which retain their surface hydroxyl groups, despite the strong hydrogen bonding between DMF and these groups referred to above. However, this adsorption is weak and reversible, since the PS... 

The attainable enrichment and clean-up in SPE depend primarily on the selectivity and affinity of the sorbent for the selected target analyte or analytes, the sample load capacity for the analytes and the rate of mass transfer to and from the binding sites, the latter affecting the minimum desorption volume and thus the enrichment that can be obtained. Other factors of importance are the reproducibility of the recovery yields and the stability and reusability of the sorbent when online procedures are desired. For hydrophobic analytes satisfactory results are usually obtained using standard reversed phase sorbents. Thus hydrophobised silica (C8, Cl8), styrene-divinylbenzene copolymers (PS-DVB) and graphitised carbon black (GCB) are the conventional sorbent materials used in SPE (Fig. 15.2)... 

The synergetic antifoaming effect of mixtures of insoluble hydrophobic particles and hydrophobic oils, when dispersed in an aqueous medium, has been weU established in the patent Hterature. These mixed antifoamers are very effective at very low concentrations (10-100 ppm). The hydrophobic particles may be hydrophobised silica and the oil is PDMS. 

Towards total hydrophobisation of MCM-41 type silica surface... 

Towards total hydrophobisation of MCM-41 type silica surface T. Martin, A. Galarneau, D. Brunei, V. Izard, V. Hulea, A.C. Blanc, S. Abramson,... 

Stereospecificity. The adsorption of isotactic, stereotactic and atactic PMMA to silica from CDCI3 was studied by IH liquid spectra, where the methyl peaks spectrally separate into isotactic, heterotactic and syndiotactic sequences. The intensity ratios of the liquid IH signals of polymers adsorbed to silica were compared to solution spectra. In Fig. 17 the comparison of traces A and D shows that the isotactic component (mm) has significantly decreased in intensity relative to the other two components in spectrum D, and a selective adsorption of i-PMMA was concluded. The stereospecificity decreased with adsorbed amount, and was also reduced for adsorption above the conformational transition temperature. Comparison to adsorption to a hydrophobised surface, which did not show stereospecific immobilisation, proved that the silica hydroxyl groups were essential to attract the isotactic component specifically [59]. 

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