Phoretic Interactions Between Active Droplets

Abstract

Concentration gradients play a critical role in embryogenesis, bacterial locomotion, as well as the motility of active particles. Particles develop concentration profiles around them by dissolution, adsorption, or the reactivity of surface species. These gradients change the surface energy of the particles, driving both their self-propulsion and governing their interactions. Here we uncover a regime in which solute-gradients mediate interactions between slowly dissolving droplets without causing autophoresis. This decoupling allows us to directly measure the steady-state, repulsive force, which scales with interparticle distance as $F\sim 1/r^2$. Our results show that the process is diffusion rather than reaction rate limited, and the theoretical model captures the dependence of the interactions on droplet size and solute concentration, using a single fit parameter, $l=16\pm 3$~nm, which corresponds to the lengthscale of a swollen micelle. Our results shed light on the out-of-equilibrium behavior of particles with surface reactivity.

5 pages, 4 figures

References in corpus (5)

• Spontaneous motion in hierarchically assembled active matter
• Physics of Microswimmers - Single Particle Motion and Collective Behavior
• Self-propulsion of pure water droplets by spontaneous Marangoni stress driven motion
• Emergent self-propulsion at low Reynolds number
• Collision between chemically-driven self-propelled drops

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• Rheotaxis of Active Droplets
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• Marangoni droplets of dextran in PEG solution and its motile change due to coil-globule transition of coexisting DNA
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• Oscillatory droplet dissolution from competing Marangoni and gravitational flows
• Arrested on heating: controlling the motility of active droplets by temperature
• Physicochemical Hydrodynamics of Droplets out of Equilibrium: A Perspective Review