ABSTRACT
Another strategy was used by Novotny's group [65,66] to shield the Si-0-Si-C linkages from the attack of high-pH solutions. In this procedure, a self-assembled alkylsilane network is formed, leading to highly stable coatings in the pH range of 2-10 for several weeks. The reagents (7-oct-1-enyltrimethoxysilane and/or allyltrimethoxysilane and/or methyltrimethoxysilane) were bonded to an HN03-pretreated capillary surface. These reagents were prehydrolyzed, to form hydrogen bonds with the surface silanol groups and with their close neighbors. After elimination of water by thermal treatment, a stable monolayer is formed. The mixed alkylsilane monolayer [65] forms a cross-linked network in which each chain is linked to the surface and to other chains via Si-0-Si linkages (Fig. 5). The coatings are more stable than with single alkylsilane layers because the C3 and C8 chains form a dense hydrophobic layer that shields the Si-0-Si linkages. The vinyl groups bonded to the capillary surface were used for further in situ copolymerization reactions to attach different hydrophilic coatings, as polymers of acrylamide [65] or of N-methacroyl-tris(hydroxymethyl)aminomethane [65] or cross-linked copolymers of 2-hydroxyethyl methacrylate (HEMA) and hydroxypropylcellulose [66]. Several interesting examples of protein separation at a high pH are given.
