兩多孔性膠體粒子間交互作用下之同軸電泳現象

Abstract

本研究以數值方法探討兩顆帶電多孔粒子間相互作用對電泳動度的影響,其中包含電雙層極化效應和電雙層重疊,且電雙層厚度和多孔粒子帶電量可任意。在外加弱電場假設下,高度耦合的電動力學方程組如電位、離子濃度和流場方程式將以微擾法線性化,並以 Chebyshev 擬譜方法求解線性化後的電動力學方程組。 為了釐清粒子間相互作用對電泳動度的影響,本研究於結果討 論探討重要的系統參數如電雙層厚度、多孔粒子固定電荷密度、摩擦係數、與粒子間距對電泳動度的影響。研究結果發現,除了相同粒子間有相互作用外,當電雙層重疊時,極化效應的影響使粒子愈靠近其電泳動度不增反降。此外在高度電雙層重疊下,粒子的電泳動度甚至會低於同情況下的單一粒子。此特別的行為是過去相關研究忽略電雙層重疊或極化效應所無法觀察到的現象,暗示著此兩個因素的重要性。本研究可作為探討均質聚電解質懸浮液電動力學現象的基礎膠體科學研究。

Electrophoresis of two charged porous spheres moving along their line of centers is investigated theoretically, where overlapping and polarization effect of electric double layers are both taken into account. The thickness of electric double layer and fixed charge density of porous spheres are arbitrary. The coupling equations of electric potential, ion concentration, and flow field are linearized by assuming that the external electric field is weak. A pseudo-spectral method based on Chebyshev polynomials is applied to numerically solve the resulting electrokinetic equations. To clarify the effect of particle interactions on the electrophoretic mobility, the effects of key parameters are examined such as the double layer thickness, fixed charge density, friction coefficient of porous particles, and surface distance between particles. The most curial finding, besides the non-zero interactions between identical particles, is that particle mobility decreases as double layer of two particles touched due to the polarization effect on the role of electric interactions. More interesting findings is that particle mobility may lower than that of the single one when high double layer overlapping is consideration. These findings was not investigated in the corresponding studies of two particle interactions where overlapping of electric double layers or polarization effect is neglected, indicating the importance of these two factors. Particle interactions between two charged porous particles can be used to describe homogeneous concentrated suspensions of polyelectrolyte in a fundamental aspect of colloid science.