Directional motion of charged particles near filter membrane br

Membrane has many applications in the fields of filtration and separation, but due to the attraction orrepulsion exerted by the membrane, the particles will experience a directional motion. As a result, two totallyopposite effects, i.e. particle enrichment and exclusion zone, take place in the vicinity of the membrane, and theunderlying reason is still not clear. In this work, colloidal particles with negative surface charge are used as amodel substance, with the advantages of monitoring the particle concentration in a real time and in situ way, toinvestigate the influence of cellulose membrane on the movement of particles. The experimental results showthat the particles are enriched in the vicinity of the membrane. The diffusiophoresis effect originating from tinynumber of 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 relevantnumerical 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-osmoticflow and particles lateral diffusion also result in the migration of particles towards the container wall, andfurther increasing the particle number near the wall.