THE FUMED SILICA SURFACE - A STUDY BY NMR

High-resolution solid-state NMR techniques were used to investigate th e surface structure of Cab-O-Sil fumed silica. H-1 NMR results obtaine d from CRAMPS, MAS-only and relaxation studies reveal the existence of both hydrogen-bonded silanols and isolated silanols on the Cab-O-Sil surface. A systematic dehydration study of fumed silica was carried ou t, with results on the quantity of each type of silanol on the surface at various dehydration stages. Si-29 CP-MAS experiments, including CP spin dynamics studies and various other relaxation studies, were empl oyed to probe hydrogen bonding and the local structural environments o f various hydroxyl groups of silica surfaces. Si-29 CP-MAS experiments on water-treated and deuterium-exchanged Cab-O-Sil indicate the exist ence of interparticle silanols and internal silanols in filmed silica. H-1 and Si-29 NMR show that for fumed silica both isolated and hydrog en-bonded silanols are present on the surface of an untreated sample, in contrast to the case of silica gel, where all silanols of an untrea ted sample are hydrogen bonded.