圓錐奈米孔道內之離子電流整流效應:聚電解質層改質方式與孔道形狀之影響

Abstract

圓錐奈米孔道因為擁有特殊的幾何形狀，它們能引起許多有趣的電動力學現象，像是離子濃度極化(ICP)以及離子電流整流效應(ICR)。我們考慮兩種圓錐奈米孔道：第一為僅將奈米孔道內之表面改質一層聚電解質層；第二為在奈米孔道內以及兩端出口外之表面全部改質一層聚電解質層。我們藉由一系列的數值模擬去探討電雙層厚度以及聚電解質層厚度對奈米孔道的離子電流整流效應的影響。我們發現第一種奈米孔道的離子濃度極化程度比第二種強。另外，當調控溶液離子濃度時，兩種奈米孔道的整流效應係數( )表現極不同。當溶液離子濃度很低時，可以在第一種奈米孔道發現其整流效應係數有翻轉的現象。 接著，我們討論表面上酸性官能基以及鹼性官能基都有並且電荷可調節的奈米孔道。並探討了奈米孔道形狀、溶液酸鹼值pH以及溶液鹽濃度對離子電流整流效應的影響。當溶液pH大於等電位點，我們發現當改變奈米孔道的曲率時，整流效應係數會出現區域最大值。相較之下，當溶液pH小於等電位點時，整流效應係數僅會隨著孔道曲率上升而單調遞增。

Due to their specific geometry, conical nanopores are capable of yielding several interesting electrokinetic phenomena, such as ion concentration polarization (ICP) and ion current rectification (ICR). Extending previous analyses, we consider two types of nanopore: only the inner surface of a nanopore is functionalized by a polyelectrolyte (PE) layer in type I nanopore, and both its outer and inner surfaces are functionalized in type II nanopore. Numerical simulation is conducted to examine the influences of the double layer thickness and the thickness of the PE layer of a nanopore on its ICR behavior. We show that the ICP in type I nanopore is more significant than that in type II nanopore. In addition, as the bulk salt concentration varies, the rectification factors ( ) for type I and II nanopore are different significantly. In particular, if the salt concentration is low, an inversion in is observed in type I nanopore. Furthermore, we consider the case where the nanopore surface has both acidic and basic functional groups, and is pH-regulated. The influences of the nanopore shape, solution pH, and bulk salt concentration on the associated ICR behavior are examined. If the solution pH exceeds the isoelectric point, the rectification factor shows a local maximum as the curvature of the nanopore surface varies. In contrast, if it is lower than the isoelectric point, that factor increases monotonically with increasing surface curvature.