CO 2 -leakage-driven diffusiophoresis causes spontaneous accumulation of charged materials in channel flow

Significance Particle-laden flow is ubiquitous in physiological and diagnostic systems, where usually the particles (e.g., colloidal particles, cells, macromolecules, etc.) gain a nonzero net surface charge when suspended in an aqueous phase. Polydimethylsiloxane (PDMS) has been the most popular material used for microfluidic fabrications for the past two decades. Its high gas permeability is well appreciated, but the possible influence of gas leakage on the motion of charged particles has not been recognized. By systematic experiments and model calculations, we demonstrate that initial (early time) gas leakage through PDMS can create a charge-dependent accumulation of particles in common channel flows by diffusiophoresis and show that the phenomenon can be applied to concentrating and collecting proteins.