Surface-directed liquid flow inside microchannels

Self-assembled monolayer chemistry was used in combination with either mult istream laminar flow or photolithography to pattern surface free energies i nside microchannel networks. Aqueous Liquids introduced into these patterne d 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 n etworks. The ability to confine Liquid flow inside microchannels with only two physical walls is expected to be useful in applications where a Large g as-liquid interface is critical, as demonstrated here by a gas-liquid react ion.