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Sedimentation of a pH-Regulated Nanoparticle in a Generalized Gravitational Field

Hsu, Jyh-Ping, Chu, Yu-You, Tseng, Shiojenn
The Journal of Physical Chemistry C 2017 v.121 no.43 pp. 24272-24281
Reynolds number, liquids, moieties, nanoparticles, pH, salt concentration
Taking account of the effect of double-layer polarization, we modeled the sedimentation of a pH-regulated nanoparticle in a generalized field. The influences of the radius and the density of the functional groups of the particle, the pH, and the bulk salt concentration of the liquid phase and the Reynolds number Re on the sedimentation behavior of the particle are examined in detail. We found that as Re increases, because more counterions are dragged away from the particle surface, its averaged charge density decreases accordingly. The smaller the particle, the thicker the double layer so that double-layer polarization is more significant and the distribution of the surface charge density is more nonuniform. Interestingly, the smaller the particle, the higher the averaged surface charge density, but the smaller the electric force acting on it. If the particle is sufficiently large (300 nm in radius), its averaged surface charge density is insensitive to Re as it varies from 0.0025 to 0.04 but can have an appreciable difference (ca. 10%) if it is small (75 nm).