Title: Forces on soft phoretic particles

Author (Talk): Sophie Marbach, Courant Institute of Mathematical Sciences, NYU

Abstract:

Phoresis of particles under gradients of electro-chemical forces (solute gradients, electric potential gradients) is a ubiquitous phenomenon. Most benchmark experiments are done on rigid particles such as colloids yet softer particles like polymers or DNA also undergo phoretic motion. As these soft particles move, one could expect them to deform under hydrodynamic stresses. For electrophoresis, it is widely known that the local force balance at the surface of the particle is ensured, and therefore, particles do not deform. However, here we show analytically that the local force at the surface of a particle undergoing diffusio-phoresis (in a gradient of solute) does not vanish. Therefore soft diffusio-phoretic particles should deform. This allows to gain physical intuition on the force balance and the relevant length scale where osmotic effects are at play. We expect these results to encourage innovative experiments to separate soft particles and to allow for better modeling of phoretic related effects.