H-2 NUCLEAR-MAGNETIC-RESONANCE INVESTIGATIONS OF THE DYNAMICS OF ALKYL-MODIFIED SILICA IN THE PRESENCE OF SOLVENT, SURFACTANT, AND MESOGENIC MOLECULES

Specifically deuterated dodecyltrichlorosilane, (Cl3Si(CH2)10CD2CH3), was synthesized and reacted with porous chromatographic grade silica to obtain a labeled alkyl-modified surface. Subsequently, 2H NMR quadrupole echo spectra were recorded, and spin-lattice relaxation times (T1) were calculated for the material in the presence of organic and hydroorganic solvents, an aqueous surfactant solution, and the nematic phase of a thermotropic liquid crystal. Line width, shape, and T1 were sensitive to changes in the interfacial conditions. The spin-lattice relaxation rate (T1-1) was found to be linearly related to the square of the line width at its half-height (Δki/22). These results suggest that the motional averaging process for the C-2H bond is a combination of fast and intermediate molecular fluctuations similar to those observed in other restricted systems such as lipid bilayers and micellar systems. © 1990, American Chemical Society. All rights reserved.