Diffusiophoretic focusing of colloids in a microfluidic T-junction

Diffusiophoretic migration of colloids due to chemical gradients has been used to manipulate and guide them in simple configurations, including co-flow channels and open/dead-end pores. In these scenarios, the colloid distribution is determined by the solute and flow velocity fields. Here, we report on an unexpected particle focusing effect in a microfluidic T-junction in the presence of a solute concentration gradient between the two sides. Using experimental observations and numerical simulations, we explain the mechanism of this focusing effect as an interplay between phoretic and osmotic flows.