DIRECTIONAL MOTION OF CHARGED PARTICLES NEAR MEMBRANE

Membrane has widely applications in the field of filtration and separation, but due to the attraction or repulsion exerted by the membrane, the particles will experience directional motion. As a result, two totally opposite effects, particle enrichment and exclusion zone, take place in the vicinity of the membrane, and the underlying reason is still not clear. In the paper, colloidal particles with negative surface charge was used as a model substance, with the advantages of monitoring the particles concentration in a real time and in situ way, to investigate the influence of cellulose membrane to the movement of particles. The experimental results showed that particles enriched in the vicinity of the membrane. The diffusiophoresis effect originates from the tiny amount ions released by the film is the main reason of the directional movement of the charged particles. Based on the two mechanisms of diffusiophoresis and diffusion, we construct a model and make relevant numerical calculation, and the numerical results are qualitatively consistent with the experimental results. Moreover, in addition to the longitudinal motion of the particles towards the filter membrane, diffusio-osmotic flow and particles lateral diffusion also result in the migration of particles towards to the container wall, and further increase particles number near the wall.