軟物質系統電動力學現象:擴散泳動暨電荷調節現象探討

Abstract

本研究主要以假性光譜法對軟物質系統之電動力學現象如電泳以及擴散泳進行數值模擬，其中討論軟物質系統包含聚電解質及凝膠系統並考慮電荷調節現象的影響。文中先針對電動力學、電荷調節現象以及各種系統及其應用作一系列文獻回顧，並說明本次研究目的；而於第二章做進一步的理論分析。第三章介紹相關數值方法。其後三章(四、五、六章)則依序針對表面調節硬粒子之凝膠電泳現象、多孔粒子於電解質溶液中的擴散泳現象以及電荷調節密集多孔系統之電泳現象等電動力學現象做深入研究分析。 研究結果發現，大體而言當粒子表面電位越高，亦或是聚電解質之高分子層固定電荷密度越高時，粒子泳動速度將隨之提升；然而相對的受外加電場�濃度場作用，其粒子周圍的離子雲扭曲也越嚴重，進而產生一誘發電場與原外加電場�濃度場競爭而降低泳動度，此現象稱為極化效應，其隨電雙層變化而造成粒子速度產生極值。極化效應的存在甚至可產生高電荷密度粒子速度低於低電荷密度粒子的特殊現象。此外，聚電解質或是凝膠之摩擦係數愈高，則使流體阻力愈大而降低泳動度。然而，摩擦係數愈高，流體對流現象減緩造成極化效應不明顯。 另一方面，電荷調節現象影響粒子電量非常顯著：當官能基解離常數愈大、pH值愈大時，有利於解離反應進行，使得解離電量較大。同時，離子強度也會影響到解離電量。

The electrokinetic behavior of soft matter including polyelectrolytes amd polymer gels is investigated, with consideration of charge-regulation phenomena. A pseudo-spectral method based on Chebyshev polynomials is used to solve the resulted general electrokinetic equations. We found, among other things, that the higher the particle surface potential or the fixed charge density of the polymer layer of the polyelectrolyte, the more serious distortion of the ion clouds, which generates an induced electric field opposite to the particle motion, thus reducing the particle mobility, as an effect referred to the polarization effect. Moreover, local extrema are observed in the mobility profile as the double layer thickness varies, which is absent in previous theoretical study which neglected the polarization effect. An interesting phenomenon is observed: a less charged particle can even move faster than a highly charged one at some situation, which is also attributed to the polarization effect. The poorer the permeability of the polyelectrolyte or the polymer gel, the slower the particle motion in general, due to the increase of the hydraulic drag force. On the other hand, we found that the charge-regualtion phenomena has dramatic impact on the elctric condition of the particle. The higher the number of functional groups and the dissociation constant of the functional groups, the greater the charge of the particle; yet the higher the pH of the solution, the lower the charge of the particle.