Interfacially driven transport in narrow channels

When colloids flow in a narrow channel, the transport efficiency is controlled by the non-equilibrium interplay between colloid-wall interactions and hydrodynamics. In this paper, a general, unifying description of colloidal dispersion flow in a confined system is proposed. A momentum and mass balance founded framework implementing the colloid-interface interactions is introduced. The framework allows us to depict how interfacial forces drive the particles and the liquid flows. The interfacially driven flow (osmotic or Marangoni flows for repulsive or attractive colloid-wall interactions respectively) can be directly simulated in 2D domains. The ability of the model to describe the physics of transport in a narrow channel is discussed in detail. The hydrodynamic nature of osmosis and the associated counter-pressure are mechanically related to the colloid-interface interactions. The simulation shows an unexpected transition from axial plug to pillar accumulation for colloidal accumulation at a channel bottleneck. This transition has important consequences in transport efficiencies. Existing limiting cases, such as diffusio-osmosis, are recovered from the simulations, showing that the framework is physically well-founded. The model generalizes the existing approaches and proves the hydrodynamic character of osmosis, which cannot be fully described by purely thermodynamic considerations. (paper)