Precise control of liquid–liquid interface position and geometry in open microchannels

Accurate control of liquid–liquid interfaces is of great importance in many scientific fields. Currently, most studies on liquid–liquid interfaces are based on microfluidics in closed channels, and for open systems, it is difficult to form stable liquid–liquid interfaces in microchannels due to the interference of gas-phase molecules. Here, we introduce a new method to manipulate the motion of the liquid–liquid interface under an open microchannel. Under the effect of surface tension, the liquid–liquid interface moves in microchannels until it encounters microstructures in the microchannels, where the force equilibrates and remains stable to form a fixed shape. The shape of the interface is regulated by adjusting the dimensions of the microchannels and microstructures as well as the positions of the microstructures in the microchannels. This spontaneous liquid–liquid interface moves, stops, and remains stable in a very convenient way. The morphology and position of the interface are well manipulated using microstructures, and the liquid–liquid interface with well-defined geometry can be made to stay in different positions to play different roles.