On-demand microfluidic droplet pinching and splitting under local confinement gradients
Phys. Rev. Fluids 10, 114201 – Published 6 November, 2025
DOI: https://doi.org/10.1103/mjf8-jhfy
Abstract
We report the pinching of an elongated liquid droplet confined in a rectangular microchannel. A local variation of the channel topography induces the droplet pinching and can lead to its breakup. The modification of the channel topography is caused by either a reversible local dilation of the channel bottom wall or a confinement gradient irreversibly printed in the channel. Interestingly, in both cases, channel height contraction of a few micrometers leads to the droplet's pinching in the direction of the channel width. If this pinching is such that the droplet is no longer confined at the level of its deformation, i.e., the liquid thread becomes three dimensional, the droplet splits in two. By minimizing the surface energy of the droplet under the channel confinement gradient, we can predict its pinching or breakup, if any. The dynamics of the droplet deformation are then captured by a semianalytical model that relies on the observation that the deformation is self-similar and assumes that most of the viscous dissipation occurs in the gutters at the corners of the channel. Conversely, we show that this kinetic model can be used to extract the channel's average topographic variation, down to a few micrometers, by measuring the droplet pinching dynamics under a classical optical microscope.
