Microscale flows: bubbles and active droplets

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• Daniel Booth (University of Warwick)
• Wednesday 05 November 2025, 13:00-14:00
• MR12.

If you have a question about this talk, please contact Emma.

Bubbles in Hele-Shaw cells: I will present a model for the motion of bubbles in a Hele-Shaw cell. I consider the regime where the bubbles are large enough to be flattened by the cell walls into a pancake-like shape, but small enough such that each bubble remains approximately circular when viewed from above. In this regime, the flow dynamics are determined by a single dimensionless parameter, the “Bretherton parameter”, and I find situations in which the bubble can travel either slower or faster than the background flow velocity. In a system of two bubbles of different radii, if the smaller bubble is in front, it will be overtaken by the larger bubble. Under certain circumstances, the bubbles may avoid collision by rolling over one another while passing. For a train of three or more bubbles moving along a Hele-Shaw channel, we observe longitudinal waves that propagate forwards or backwards along the bubble train, depending on flow conditions, resembling a Hele-Shaw Newton’s cradle.

Controllable flow through active droplets: Precise, localised flow control in microfluidic devices remains a difficult challenge. In this talk, I demonstrate, theoretically, how active droplets might be harnessed to overcome this challenge. Active droplets are produced along the microchannel wall via stimulation of a responsive hydrogel, and the ensuing phoretic slip flows drive transport and mixing in the microfluidic device.

This talk is part of the Institute of Theoretical Geophysics lunchtime seminar series.

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