鹽類價數與奈米通道之幾何形狀對其整流行為的影響

Abstract

在奈米流體尺度下，電雙層重疊效應顯著，使奈米通道可引起許多有趣的電動力學現象，如離子濃度極化(ICP)和離子電流整流(ICR)，也因而製備與合成奈米通道成為奈米科技上的一股熱潮。在第一章節中，我們利用數值模擬的方法，考慮不同電解質溶液LaCl3、CaCl2、KCl、KNO3、K2SO4，研究其離子價數比之不對稱性對圓錐形奈米通道的離子整流效應所造成的影響。改變價數比時有兩種方式，第一種方式是固定陰離子的價數，改變陽離子的價數;而第二種則是固定陽離子的價數，改變陰離子的價數。我們發現，離子強度與離子擴散係數對其電動力學現象扮演著舉足輕重的角色。另外，定性上帶正電的奈米通道之整流行為與帶負電的奈米通道相似。第二章節中，我們則是討論一表面具有pH可調節電荷之兩性離子基團的仿生雪茄形奈米通道。考慮在外加電場作用下，溶液酸鹼值pH、溶液鹽濃度、底端的開口半徑以及奈米通道形狀對離子傳輸行為的影響。藉由調節孔口半徑與表面曲率以得到雪茄形奈米通道的最佳整流表現與離子選擇性。除了能夠解釋相關電動力學現象之外，所獲得的結果還為相關設備的複雜設計提供了必要的資訊。

The overlapping of electric double layer in a nano-scaled system is usually significant, rendering it having profound and interesting electrokinetic phenomena, such as ion concentration polarization (ICP) and ion current rectification (ICR), and thus fabrication of nanodevices becomes a trend of nanotechnology. In Chapter 1, by taking account of various electrolyte solution LaCl3、CaCl2、KCl、KNO3, and K2SO4, a thorough numerical simulation is conducted to illustrate the influence of asymmetry of various ionic valence ratio on the ICR behavior in a conical nanochannel. We show that the electrokinetic phenomena depend highly on ionic strength and ion diffusivity. The qualitative behavior of the ion current rectification of a positively charged conical nanochannel is similar to that of a negatively charged one.In Chapter 2, we consider a bioinspired cigar-shaped nanochannel where its surface is pH-regulated, and has zwitterionic groups. The influences of the solution pH, the bulk concentration, the base opening radii, and the nanochannel shape on the associated ICR behavior and ionic selectivity are examined, focusing on discussing the underlying mechanisms in detail. We show that the best nanochannel performance can be achieved by adjusting the base orifice radii and surface curvature appropriately. In addition to proposing underlying mechanisms for the phenomena observed, the results gathered in this study also provide necessary information for designing relevant devices.