奈米孔道內之離子傳輸現象:孔道形狀、帶電條件與聚電解質內官能基分布之影響

Abstract

受益於近年來奈米科技的發展,孔道半徑得以達奈米尺度,而發生特殊的離子選擇性現象,基於此現象所做成的奈米流體裝置廣泛的被應用在包括,除鹽、過濾、鹽濃差及壓差發電、離子檢測以及離子電流整流。許多個別文獻在實驗中都已經能蝕刻出不同的孔道形狀,但缺乏在相同基準之下的性能比較。第一節中透過理論計算,在盡可能相同的條件與基準下,比較不同的孔道形狀以及帶電條件對於離子傳輸現象的影響。我們觀察到整流比大小主要受孔道內部體積的影響、選擇性同時會受孔道內部體積與狹窄區間範圍的影響。在不對稱雙極孔道中,孔道選擇性為零時的壁上正負電的交界處位置,同時也是整流比最大值發生的位置,另外也觀察到雙極孔道中心處與孔道壁處會有相反方向的電滲流。以上的研究成果已發表於期刊 Colloids and Surfaces A: Physicochemical and Engineering Aspects.而我們為了近一步提升奈米孔道的性能,會在孔道壁上修飾一層聚電解質。第二節中,我們在一個錐形孔道壁上修飾一層帶電會受 pH 值影響的聚電解質,並且探討其中的官能基若是均勻分布、集中在孔道壁一側或是集中在聚電解質與液體的交界處,對於電動力學現象的影響。結果發現官能基若集中在壁側,會使得整體流體阻力下降,進而提升電滲流大小,這樣的官能基分布,也會使得孔道內部離子濃度分布較不均勻,導致較大的擴散通量,進而影響其它電動力學的表現。

Benefiting from the recent advancements in nanotechnology, the radius of nanopores has reached the nanoscale, leading to unique ion selective phenomena. Based on this phenomenon, nanofluidic devices have been widely applied in various areas, including desalination, filtration, salinity gradient and pressure-driven energy generation, ion detection, and ion current rectification. While individual studies have successfully etched nanopores with different shapes, there is a lack of performance comparison under the same basic. In chapter 1, through theoretical calculations, we compare the effects of different nanopore shapes and charged conditions on ion transport phenomena under conditions as similar as possible. We observe that the rectification factor is mainly influenced by the internal volume of the nanopore, while selectivity is influenced by both the internal volume and the narrow region of the pore. In asymmetric bipolar nanopores, the position of junction location between positive and negative charges on the pore walls, where selectivity is zero, also corresponds to the maximum rectification factor. Additionally, we observe opposing electroosmotic flow directions at the center and the wall of the bipolar nanopores. These research findings have been published in the journal Colloids and Surfaces A: Physicochemical and Engineering Aspects. In recent years, to further enhance the performance of nanopores, a layer of polyelectrolyte is often modified on the pore surface. In chapter 2, we investigate the electrokinetic phenomena on a conical nanopore surface modified with a pH-regulated polyelectrolyte. We explore the effects of the functional groups are clustered near the PE- liquid interface, and near the nanopore surface on the electrokinetic phenomena. The results show that the functional groups are clustered near the nanopore surface reduces the overall fluid resistance, thereby enhancing the electroosmotic flow. This kind of distribution of functional groups also leads to uneven ion concentration distribution inside the nanopore, resulting in a larger diffusion flux and affecting other electrokinetic performances.