Transport theories based on the continuum hypothesis may not be appropriate at the nanoscale in view of surface effects. We employed molecular dynamics simulations to study the effects of confinement and concentration on diffusive transport of glucose in silica nanochannels (10 nm or smaller). We found that glucose modifies the electrical properties of nanochannels and that, below 5 nm in channel height, glucose adsorption and diffusivity are significantly reduced. With increasing concentration, the diffusivity is reduced linearly in the bulk, while it is reduced nonlinearly at the interface. The effective diffusivity reduction is related to the interface thickness, which can be 2-4 nm depending on concentration, and has an unexpected reduction at low concentrations. Results suggest that nanochannels present a one-dimensional cage environment that affects diffusivity in a fashion similar to cage-breaking diffusion. Our simulation results, consistent with the experimental observations presented here, suggest that nanoconfinement is the essential cause of the observed altered fluid diffusive transport, not accounted for by classical theories, because of coupling of confinement and concentration effects.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry