A Study of the Structure and Dynamics of Dimethyloctadecylsilyl-Modified Silica Using Wide-Line 2HNMR Techniques

Article abstract of DOI:10.1021/ja00017a001

The structure and dynamics of dimethyloctadecylsilyl-modified silica gel (C₁₈-dilica) were studied by using solid-state 2H NMR techiques.In order to reproduce with a theoretical model the 2H line shapes that were observed for the C₁₈-silica samples, it was necessary to assume that a variety of environments are present on the C₁₈-silica surface and that this heterogeneity results in different details of the motion of silane groups that are bonded to different regions of the C₁₈-silica surface. 2H spectra that were taken on the C₁₈-silica samples at temperatures below room temperature appear to be superpositions of two line shapes, indicating that some silane groups move with a simple two-site jump moiion, along with others that move with a more complex distribution of motions.At -50 deg.C, the addition of wetting liquids can affect the 2H line shape; different liquids can have dramatically different effects on the observed 2H line shapes.Simple surface structures for C₁₈-silica are proposed that are consistent with the NMR data observed in this study.