邊界效應對膠體粒子擴散泳之影響

Boundary effects on diffusiophoresis motion of colloidal spheres

施俊羽(Chun-Yu Shih)

指導教授 ： 李克強

國立臺灣大學/工學院/化學工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00451

摘要

本論文探討一膠體粒子在多種不同邊界效應之下的擴散泳運動現象。我們首先討論固定電位下硬球在孔洞模型(cavity)中的擴散泳，並且進ㄧ步將固定電位條件置換為表面調節(charge regulation)，最後我們在將系統拓展至球對自由液面(free surface)，並且考慮在不同電解質溶液且不同邊界效應下的擴散泳速度。將低表面電位的限制進ㄧ步拓展至任意表面電位的情形，利用正交配位法及牛頓-拉福生疊代法求解系統的非線性電場及流場方程式。

研究結果發現，當擴散係數不相等，為了維持整體的電中性，導致系統產生一額外的感應電力，使得特定電性的膠體粒子運動有加速的效果。而在運動過程中隨著 的增加，擴散泳動度都會產生一局部極值。體積分率較高的粒子，在運動的過程中受到的空間障礙也相對增加，使得擴散泳動度也隨之減低，造成極化效應的發生有延遲的效果。而在自由液面情況，我們考慮到球與液面距離，發現粒子的行為與電雙層受自由液面的擠壓有很大關係。

關鍵字

擴散泳 ； 雙球座標 ； 邊界效應 ； 電雙層 ； 正交配位法

並列摘要

The diffusiophoretic behavior of a colloidal sphere, at different boundary effect is investigated in this study. Two kinds of representative cases are discussed here. One is that the diffusiophoresis of a spherical particle in a spherical cavity, and the other one is that the diffusiophoresis of a spherical particle normal to a free surface. Except for constant surface potential, the effect of charge regulation is also considered here. The restriction of low zeta potential is extend to the case of arbitrary zeta potential, and solved simultaneously by pseudo-spectral method.

We find that an electrophoretic effect is generated due to an induced electric field along the direction of the bulk concentration gradient when the diffusion velocity of cations is different from that of anions. This induced electric filed can affect the motion of the particle in accordance with the charged condition on the particle. Furtermore, the diffusiophoretic velocity of the particle reaches a local maximum with the increase of . The steric hindrance for the fluid flow also becomes serious if the volume fraction of particles gets higher. As for the case of free surface, the free surface boundary can deform the double layer around the particle, and thus the diffusiophoresis of the particle becomes more complicated than that before.

並列關鍵字

diffusiophoretic ； boundary effect ； numerical method

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