Spontaneous pulse generation in a steady channel flow of a colloidal suspension

We present experiments demonstrating the spontaneous generation and traveling of a colloidal pulse in a steady channel flow. When deionized (DI) water with suspended positively-charged particles flows steadily through a single channel, a pulse of particles is generated, which then flows through the channel at a slower speed than the mean flow velocity. With detailed experimental investigations and quantified results, we rationalize our observations by considering CO₂ driven diffusiophoresis. The concentration gradient of ions in the liquid phase is created by the leakage of CO₂ through the permeable PDMS walls. Mathematical models for early stage particle focusing and the traveling pulse will be compared with the experimental observations.