Geometry-Dependent Drying in Dead-End Nanochannels.

Abstract

Liquid drying in nanoporous media is a key process in food, textile, oil and energy industries, but the corresponding kinetics remains poorly understood due to the structural complexity of nanoporous media. Here, we directly observe the drying process and study drying kinetics in single two-dimensional (2-D) nanochannels with height ranging from 29 to 122 nm. Two different drying behaviors are discovered in such nanoconfinements: continuous meniscus receding and discontinuous meniscus receding due to liquid bridge formation ahead of the meniscus, albeit similar drying rates. The geometry dependence of the measured drying rates is studied at different humidities and compared with a theoretical model considering liquid corner flow, liquid thin film flow, and vapor diffusion as contributors to the overall drying rates. Individual contributions from vapor and liquid transport inside the nanochannels to the drying kinetics are decoupled, and the water vapor diffusivity is successfully extracted. Our results show that both corner flow and vapor diffusion play important roles on water drying in nanochannels without sharp corners. Our findings further indicate that water vapor diffusion in nanoscale confinements can still be described by the classic Knudsen diffusion theory. These results provide new insights of liquid drying in nanoporous media and have implication in optimizing drying processes in industrial applications.