Abstract
Abstract
Summary: The self-diffusion coefficient of MAO confined within a silica membrane is not experimentally accessible by traditional PFG NMR measurements, probably due to a susceptibility effect resulting in rather broad, unobservable resonance lines. A more indirect approach was therefore applied to probe the diffusivity of MAO within a silica membrane. MAO confined in a bulk toluene solution on one side of the membrane was free to diffuse through the membrane (saturated with toluene) and into a corresponding deuterated toluene solution on the other side of the membrane where its proton NMR signal intensity was monitored as a function of time. By introducing a relevant diffusion model, the diffusivities of both toluene and MAO were derived by model-fitting. By refining the diffusion model, the formation of methane within the silica was explained, and its diffusivity estimated. The results suggest a significant reduction in diffusivities of both MAO and toluene within the silica as compared to the corresponding diffusivities in bulk solution.
Summary: The self-diffusion coefficient of MAO confined within a silica membrane is not experimentally accessible by traditional PFG NMR measurements, probably due to a susceptibility effect resulting in rather broad, unobservable resonance lines. A more indirect approach was therefore applied to probe the diffusivity of MAO within a silica membrane. MAO confined in a bulk toluene solution on one side of the membrane was free to diffuse through the membrane (saturated with toluene) and into a corresponding deuterated toluene solution on the other side of the membrane where its proton NMR signal intensity was monitored as a function of time. By introducing a relevant diffusion model, the diffusivities of both toluene and MAO were derived by model-fitting. By refining the diffusion model, the formation of methane within the silica was explained, and its diffusivity estimated. The results suggest a significant reduction in diffusivities of both MAO and toluene within the silica as compared to the corresponding diffusivities in bulk solution.