Surface-Directed Liquid Flow Inside Microchannels

TLDR

The maximum pressure that keeps liquid confined in patterned microchannels depends on the liquid’s surface free energy, its advancing contact angle on hydrophobic regions, and channel depth. The authors used self‑assembled monolayer chemistry with multistream laminar flow or photolithography to pattern surface free energies, then introduced aqueous liquids that remain confined to hydrophilic pathways as long as pressure stays below the critical value. Surface‑directed liquid flow enabled pressure‑sensitive switches in channel networks, and the confinement of liquid with only two physical walls proved useful for gas‑liquid reactions where a large interface is required.

Abstract

Self-assembled monolayer chemistry was used in combination with either multistream laminar flow or photolithography to pattern surface free energies inside microchannel networks. Aqueous liquids introduced into these patterned channels are confined to the hydrophilic pathways, provided the pressure is maintained below a critical value. The maximum pressure is determined by the surface free energy of the liquid, the advancing contact angle of the liquid on the hydrophobic regions, and the channel depth. Surface-directed liquid flow was used to create pressure-sensitive switches inside channel networks. The ability to confine liquid flow inside microchannels with only two physical walls is expected to be useful in applications where a large gas-liquid interface is critical, as demonstrated here by a gas-liquid reaction.