  Electro- and diffusio- phoresis of particles correspond respectively to the
transport of particles under electric field and solute concentration gradients.
Such interfacial transport phenomena take their origin in a diffuse layer close
to the particle surface, and the motion of the particle is force-free. In the
case of electrophoresis, it is further expected that the stress acting on the
moving particle vanishes locally as a consequence of local electroneutrality.
But the argument does not apply to diffusiophoresis, which takes its origin in
solute concentration gradients. In this paper we investigate further the local
and global force balance on a particle undergoing diffusiophoresis. We
calculate the local tension applied on the particle surface and show that,
counter-intuitively, the local force on the particle does not vanish for
diffusiophoresis, in spite of the global force being zero as expected.
Incidentally, our description allows to clarify the osmotic balance in
diffusiophoresis, which has been a source of debates in the recent years. We
explore various cases, including hard and soft interactions, as well as porous
particles, and provide analytic predictions for the local force balance in
these various systems. The existence of local stresses may induce deformation
of soft particles undergoing diffusiophoresis, hence suggesting applications in
terms of particle separation based on capillary diffusiophoresis.
