The kinetics of mass transfer in a stagnant fluid layer
next to
an interface govern numerous dynamic reactions in diffusional micro/nanopores,
such as catalysis, fuel cells, and chemical separation. However, the
effect of the interplay between stagnant liquid and flowing fluid
on the micro/nanoscopic mass transfer dynamics remains poorly understood.
Here, by using liquid cell transmission electron microscopy (TEM),
we directly tracked microfluid unit migration at the nanoscale. By
tracking the trajectories, an unexpected mass transfer phenomenon
in which fluid units in the stagnant liquid layer migrated two orders
faster during gas–liquid interface updating was identified.
Molecular dynamics (MD) simulations indicated that the chemical potential
difference between nanoscale liquid layers led to convective flow,
which greatly enhanced mass transfer on the surface. Our study opens
up a pathway toward research on mass transfer in the surface liquid
layers at high spatial and temporal resolutions.