VIBRATIONAL ROTATIONAL CORRELATION-FUNCTION APPLIED TO CHEMICALLY MODIFIED SURFACES

The current study represents the first application of the vibrational-rotational correlation function (VRCF) to analyze band shapes in systems where molecular motion is hindered by surface anchoring through chemical bonding. Preliminary VRCF curves are reported as a function of temperature for the CN stretch at 2227 cm-1 and the asymmetric CD stretch at 2218 cm-1 for silica chemically modified via silanization with either (2-cyanoethyl)dimethylchlorosilane or ([12-H-2]dodecyl)dimethylchlorosilane. In a general sense, the decay of the correlation function for the surface-bound systems can be described in terms of a shorter time region of negative curvature and a longer time region that is approximately exponential. Further, the negative natural logarithm of the correlation function at a fixed time in the longer time region appears to be linearly related to temperature. However, over an extended thermal range, biphasic behavior has been observed for the intermediate chain length deuteriomethyl system. This latter behavior is consistent with similar trends in nuclear magnetic resonance, gas chromatographic, and differential scanning calorimetric data and may be due to a thermally conformational change in the bonded alkyl chains.