Physical Review Fluids

In a crowded and confined system where many drops interact, how do the interactions give rise to collective behavior? How do these interactions impact the performance of droplet-based microfluidic technology, and how can we overcome or leverage such interactions? This paper reviews our recent work on answering these questions, by studying the collective behavior of droplets in a concentrated emulsion and tracking the dynamics and the fate of individual droplets within the emulsion in a microfluidic system.

The formation of raindrops in clouds requires the collision and coalescence of water droplets. The rapidity of this process has long been a puzzle in atmospheric fluid dynamics. We review one possible explanation - inertial particle caustics around strong vortices. We apply this simple physical picture to data from direct numerical simulations of highly turbulent flow, and show that caustics around vortices can, at high Reynolds number, provide the seed for the rapid formation of larger droplets, and thus rain, in ice-free clouds.

How do microorganisms move in fluids that contain particles and/or polymers? Such fluids often display nonlinear rheological behavior such as shear-rate dependent viscosity and viscoelasticity. The effects of such rheological behavior on the swimming behavior of microorganism at low Reynolds number are only recently being elucidated. This article highlights a few of the key developments in the field of swimming in complex fluids.

According to the definition by $Oxford$ $Languages$, style is $a$ $particular$ $procedure$ $by$ $which$ $something$ $is$ $done$ and thus perfectly fits with what we express in a technical paper; but it also designates $a$ $distinctive$ $appearance,$ $typically$ $determined$ $by$ $the$ $principles$ $according$ $to$ $which$ $something$ $is$ $designed.$ This, that might be less clear in a scientific context, is precisely what we discuss in our paper devoted to the question of style in science. The figure shows a tear by van der Weyden, circa 1435.