邊界效應對軟性膠體粒子擴散泳行為之影響

Abstract

近年來關於擴散泳的研究文獻指出，離子濃度梯度可被用在奈米科技及電動力學相關應用上。因此，本論文以有限元素法探討膠體粒子在不同邊界影響下之擴散泳行為。我們考慮兩種代表性的邊界效應:離子濃度梯度方向垂直或平行於所假設之邊界，分別模擬在兩雙平板間或沿一圓柱形孔洞泳動的問題。為符合實際之應用範疇，本論文分別探討硬球、軟球(包含一硬性球核及一多孔性外層)以及全軟球三種膠體粒子之擴散泳行為。本論文完整分析了擴散泳中包含電雙層極化、擴散滲透阻流、電泳、電滲透阻流、遮蔽效應、鬆弛極化效應、反離子極化及同離子擴散等複雜現象。本論文亦探討離子濃度梯度對一帶電奈米孔洞造成之擴散滲透流以及離子濃度極化現象。數值模擬的結果顯示，各種邊界效應、膠體粒子自身之物理性質、電雙層厚度、電解質種類等因素對於擴散泳行為有顯著的影響。本論文所獲結果提供擴散泳相關應用領域具參考價值之資訊。

Recent reports on the diffusiophoretic phenomenon have revealed that the salt concentration gradient can be applied in nano-technological applications. This study investigated the boundary effects on the diffusiophoresis of colloidal particle through finite element method. We considered the direction of diffusiophoresis is either normal or parallel to a boundary, using two parallel disks and a cylindrical pore as an example, respectively. Three types of colloidal particle are modeled: a rigid sphere, a soft sphere (comprising a rigid sphere and a porous layer) or an entire porous sphere. We presented thoroughly the sub-mechanisms such as double-layer polarizations, diffusioosmotic retardation flow, electrophoresis, electrophoretic retardation flow, shielding effect, relaxation effect, polarization of condensed counterions and diffusion of coions across the porous particle. Diffusioosmosis and ion concentration polarization near a charged nanopore are also presented. Numerical results reveal that the sub-mechanisms, and hence the diffusiophoretic behavior depend strongly upon the boundary effects, the physical nature of the particle and/or the bulk ionic concentration.