Jozef Hodyl PhD Thesis - Theses - Flinders University

Si-OH +- OH SiO - + H 2 OFor surface immobilisation of a substrate it is imperative that the number ofavailable silanol groups on the silica surface is maximised as they are the reactivespecies utilised in surface modification processes. 132, 136, 149, 151 This is commonlydone by heating the silica to 423 K under vacuum. Immobilising the functional groupdirectly onto the silanol groups on the silica surface has disadvantages and hence it isdesirable to append a linkage between the surface and the functional group. 136 Linkermolecules are generally silane coupling agents that contain reactive moieties at eachterminus. 152 They are able to attach to the surface of silica by reacting with thesurface silanol groups. Once attached to silica they are able to retain some form offunctionality at their periphery, such as an aminopropysilane which uses the terminalamino group as the reactive centre for further functionalisation. The terminus thatreacts with the surface silanol groups tends to be composed of hydrolysable groupssuch as chloro or alkoxy moieties. 152 Three examples of silane coupling agents are 3-(aminopropyl)trimethoxysilane, 30, vinyltrichlorosilane, 31, and, 3-(glycidoxypropyl)trimethoxysilane, 32.30 31 32These coupling reagents readily react with a silica surface to produce an array oflinkers capable of covalently binding to a molecule of interest, as shown in Figure1.13, for a single molecule of 32 covalently attached to silica to form Si-GPS, 33.27