Diffusiophoresis of a highly charged conducting fluid droplet

Abstract

Diffusiophoresis of a perfectly conducting droplet-like liquid metal in electrolyte solutions is investigated theoretically, focusing on the chemiphoresis component, the very heart of diffusiophoresis, where the droplet motion is induced solely by the chemical gradient. The resulting electrokinetic equations are solved with a pseudo-spectral method based on Chebyshev polynomials. For the isothermal electrokinetic system of a perfectly conducting droplet considered here, there is no Marangoni effect, which is a motion-inducing effect due to the variation of interfacial tension along the droplet surface. No Maxwell traction is present as well. The droplet motion is full of hydrodynamic nature. It is found, among other things, that contrary to a dielectric droplet, a conducting droplet always moves up the chemical gradient toward the region with a higher concentration of ions in chemiphoresis. This implies that a perfectly conducting droplet like a gallium or its alloy droplet is superior to the commonly utilized dielectric droplet like a liposome in drug delivery in terms of self-guarding itself toward the desired destination of injured or infected area in the human body, as specific ionic chemicals are often released there. Optimum droplet size yielding the fastest migration rate is predicted.