Mass Transport of Volatile Molecules in Porous Materials: Evaporation–Condensation Phenomena Described by NMR Diffusometry

The transport mechanism of benzene in chromatographic-grade porous silica gel (10 nm pore size, 5 μm sphere diameter) was described by pulsed-field gradient (PFG) high-resolution magic-angle spinning (HRMAS) NMR by measuring the molecular mobility in a series of samples with variable filling levels of the void volume. The relevance of vapor-phase diffusion for benzene, pure or dissolved in chloroform, was established, and it implies migration of benzene between silica particles through an evaporation–condensation mechanism.