雙性聚電解質的擴散泳：粒子形狀與帶電管道的效應

Abstract

考量到近年來擴散泳在生物感測技術中的應用，我們模擬了電荷可調解之雙性聚電解質在多離子溶液中的擴散泳模型，特別是粒子形狀與帶電邊界對粒子擴散泳行為的影響。在前者中，我們延伸了過去對環形聚電解質分析從固定電荷密度到電荷可調節模型。藉由改變官能基密度、尺寸、軟硬度、溶液pH值和電解液濃度來測量環形聚電解質在不同情況下的擴散泳行為，我們的結果顯示環形聚電解質的擴散泳行為和相對應的球形有定量和定性上的差距。在後者中，我們藉由改變溶液pH值、電解液濃度和奈米管道半徑來模擬球形聚電解質在二氧化矽奈米管道的擴散泳行為。聚電解質和奈米管道的電雙層之間的交互作用預期會影響聚電解質旁的電場、流場和離子分佈，而對擴散泳行為產生重要的影響。其中，擴散泳速度的強度和方向皆與所假設的條件息息相關，代表我們所得的結果可以輔助設計出有效的分離程序。

Considering recent applications of diffusiophoresis in biosensing technology, we model the diffusiophoresis of a zwitterionic, pH-regulated polyelectrolyte (PE) in a solution containing multiple ionic species. In particular, the influences of particle shape and charged boundary are discussed. In the former, we extend previous analysis for the diffusiophoresis of a toroidal PE at a fixed charge density to the case of pH-regulated condition. The diffusiophoretic behaviors of the toroidal PE considered under various conditions are examined by varying its functional group density, size, and softness, and the solution pH and bulk salt concentration. We show that the diffusiophoretic behavior and the effective charge density of a toroidal PE can be different both quantitatively and qualitatively from the corresponding spherical PE. In the latter, we simulate the diffusiophoretic behaviors of a spherical PE in a silicon dioxide nanochannel by varying the solution pH, the bulk salt concentration, and the nanochannel radius. In this case, the interaction of the double layer of the PE and that of the nanochannel influences significantly the electric, the flow, and the ionic concentration fields near the PE, yielding profound diffusiophoretic behaviors. We show that both the magnitude and the direction of diffusiophoretic velocity depend highly on the conditions assumed in these two chapters, implying that an efficient separation process can be designed.