Quasielastic neutron scattering study of the dynamics of 1,3-diphenylpropane grafted to the pore surface of MCM-41

An initial study of the dynamics of 1,3-diphenylpropane (DPP, $\equiv $Si-O-C$_{6}$H$_{4}$(CH$_{2})_{3}$C$_{6}$H$_{5})$ attached to the surface of the mesoporous silica MCM-41 has been carried out using quasielastic neutron scattering. Measurements of the elastic intensity were carried out in the temperature range 50-380 K and indicate a trend in DPP dynamics with changing grafting density and pore size. Full quasielastic scans over an energy range of $\pm $ 17 $\mu $eV were carried out at temperatures of 240 K, 280 K, and 320 K. Initial analysis employed a stretched exponential to model the Fourier transformed data in the time domain. An average relaxation time, defined as $<\tau >$ = ($\tau $/$\beta )\Gamma $(1/$\beta )$ where $\beta $ is the stretched exponent in the model, shows a dependence on temperature, pore size, and DPP grafting density. Molecular dynamics simulations using a model for DPP grafted onto the surface of MCM-41 was compared with the experimental results.