Miansari Morteza, Friend James R, Yeo Leslie Y
Department of Mechanical and Aerospace Engineering Monash University Clayton VIC 3800 Australia; Micro/Nanophysics Research Laboratory RMIT University Melbourne VIC 3001 Australia.
Micro/Nanophysics Research Laboratory RMIT University Melbourne VIC 3001 Australia.
Adv Sci (Weinh). 2015 May 8;2(6):1500062. doi: 10.1002/advs.201500062. eCollection 2015 Jun.
Furthering the promise of graphene-based planar nanofluidic devices as flexible, robust, low cost, and facile large-scale alternatives to conventional nanochannels for ion transport, we show how the nonlinear current-voltage (-) characteristics and ion current rectification in these platforms can be enhanced by increasing the system asymmetry. Asymmetric cuts made to the 2D multilayered graphene oxide film, for example, introduces further asymmetry to that natively inherent in the structurally symmetric system, which was recently shown to be responsible for its rectification behavior due to diffusion boundary layer fore-aft asymmetry. Supported by good agreement with theory, we attribute the enhancement to the decrease in the limiting current in the positive bias state in which counter-ion trapping occurs within the negatively charged graphene oxide sheets due to increased film permselectivity as its cross-section and surface charge distribution is altered on one end; these effects being shown to be sensitive to the electrolyte pH. Further, we show that an imbalance in the pH or concentration in the microreservoirs flanking the film can also increase asymmetry and hence rectification, in addition to displaying a host of other phenomena associated with the - characteristics of typical nanochannel electrokinetic systems.
为了推动基于石墨烯的平面纳米流体器件成为传统纳米通道用于离子传输的灵活、坚固、低成本且易于大规模制备的替代方案，我们展示了如何通过增加系统不对称性来增强这些平台中的非线性电流 - 电压（I - V）特性和离子电流整流。例如，对二维多层氧化石墨烯膜进行不对称切割，会给结构对称系统中原本固有的不对称性引入进一步的不对称性，最近研究表明，由于扩散边界层前后不对称，这种固有不对称性是其整流行为的原因。在与理论良好吻合的支持下，我们将这种增强归因于正偏置状态下极限电流的降低，在这种状态下，由于膜的横截面和表面电荷分布在一端发生改变，导致膜的选择性透过性增加，负离子会被困在带负电的氧化石墨烯片内；这些效应被证明对电解质pH值敏感。此外，我们还表明，除了表现出与典型纳米通道电动系统的I - V特性相关的一系列其他现象外，膜两侧微储液器中pH值或浓度的不平衡也会增加不对称性，从而增强整流效果。
