Influence of APTES-Decorated Mesoporous Silica on the Dynamics of Ethylene Glycol MoleculesInsights from Variable Temperature ²H Solid-State NMR

The physicochemical effects of decorating pore walls of high surface area materials with functional groups are not sufficiently understood, despite the use of these materials in a multitude of applications such as catalysis, separations, or drug delivery. In this study, the influence of 3-amino-propyl triethoxysilane (APTES)-modified SBA-15 on the dynamics of deuterated ethylene glycol (EG-d4) is inspected by comparing three systems: EG-d4 in the bulk phase (sample 1), EG-d4 confined in SBA-15 (sample 2), and EG-d4 confined in SBA-15 modified with APTES (sample 3). The phase behavior (i.e., melting, crystallization, glass formation, etc.) of EG-d4 in these three systems is studied by differential scanning calorimetry. Through line shape analysis of the 2H solid-state NMR (2H ssNMR) spectra of the three systems recorded at different temperatures, two signal patterns, (i) a Lorentzian (liquid-like) and (ii) a Pake pattern (solid-like), are identified from which the distribution of activation energies for the dynamic processes is calculated employing a two-phase model