Oblique interface shearing (OIS): single-step microdroplet generation and on-demand positioning.

A new process for simultaneous generation and positioning of microdroplets within a single step named oblique interface shearing (OIS) is reported based on the observation that liquid microdroplets generated by vibrating a thin capillary across the air-liquid interface at an oblique angle exhibit notable lateral displacements. An analytical model is established to describe the lateral droplet displacement induced by the Stokes drift effect. The dependency of the lateral displacement on typical operating parameters allows for on-demand droplet positioning while they are produced. The efficacy of the process is validated through delivering microdroplets with the same size to different positions as well as size-dependent positioning of these microdroplets.