Influence of Charge-Regulated Nature on the Sedimentation of Particle and the Ionic Transport in a Conical Nanopore

• Main Authors: Yu-You Chu, 朱育佑
• Other Authors: Jyh-Ping Hsu
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/e3gduy

碩士 === 國立臺灣大學 === 化學工程學研究所 === 106 === Taking account of the effect of double layer polarization, we first modeled the sedimentation of a pH-regulated nanoparticle in a generalized field in chapter 1. 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). In chapter 2, we extend previous electrokinetic analyses based on a Newtonian fluid to power-law fluids, investigating the ion current rectification (ICR) and ion selectivity behaviors of conical nanopores having a pH-regulated surface. The bulk salt concentration, the solution pH, and the power-law index n are examined in detail for their influences on these behaviors. We show that the ICR ratio for the case where pH is lower than the isoelectric point (IEP) of the nanopore surface is different both quantitatively and qualitatively from that for the case where pH is higher than IEP. The relative magnitude of this ratio as n varies depends largely on the level of the bulk salt concentration. In contrast, the ion selectivity for pH<IEP is qualitatively similar to that for pH>IEP, where its absolute value decreases with increasing bulk salt concentration. In general, this value increases with decreasing n (more non-Newtonian). Mechanisms are proposed for explaining the observed behaviors in the ICR ratio.