Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar, 140001, India.
Sci Rep. 2022 Feb 15;12(1):2547. doi: 10.1038/s41598-022-06079-w.
The ionic current rectification (ICR) is a non-linear current-voltage response upon switching the polarity of the potential across nanopore which is similar to the I-V response in the semiconductor diode. The ICR phenomenon finds several potential applications in micro/nano-fluidics (e.g., Bio-sensors and Lab-on-Chip applications). From a biological application viewpoint, most biological fluids (e.g., blood, saliva, mucus, etc.) exhibit non-Newtonian visco-elastic behavior; their rheological properties differ from Newtonian fluids. Therefore, the resultant flow-field should show an additional dependence on the rheological material properties of viscoelastic fluids such as fluid relaxation time [Formula: see text] and fluid extensibility [Formula: see text]. Despite numerous potential applications, the comprehensive investigation of the viscoelastic behavior of the fluid on ionic concentration profile and ICR phenomena has not been attempted. ICR phenomena occur when the length scale and Debye layer thickness approaches to the same order. Therefore, this work extensively investigates the effect of visco-elasticity on the flow and ionic mass transfer along with the ICR phenomena in a single conical nanopore. The Poisson-Nernst-Planck (P-N-P) model coupled with momentum equations have been solved for a wide range of conditions such as, Deborah number, [Formula: see text], Debye length parameter, [Formula: see text], fluid extensibility parameter, [Formula: see text], applied electric potential, [Formula: see text], and surface charge density [Formula: see text] and [Formula: see text]. Limited results for Newtonian fluid ([Formula: see text], and [Formula: see text]) have also been shown in order to demonstrate the effectiveness of non-Newtonian fluid behaviour over the Newtonian fluid behaviour. Four distinct novel characteristics of electro-osmotic flow (EOF) in a conical nanopore have been investigated here, namely (1) detailed structure of flow field and velocity distribution in viscoelastic fluids (2) influence of Deborah number and fluid extensibility parameter on ionic current rectification (ICR) (3) volumetric flow rate calculation as a function of Deborah number and fluid extensibility parameter (4) effect of viscoelastic parameters on concentration distribution of ions in the nanopore. At high applied voltage, both the extensibility parameter and Deborah number facilitate the ICR phenomena. In addition, the ICR phenomena are observed to be more pronounced at low values of [Formula: see text] than the high values of [Formula: see text]. This effect is due to the overlapping of the electric double layer at low values of [Formula: see text].
离子电流整流 (ICR) 是指在跨纳米孔的电势极性切换时出现的非线性电流-电压响应，类似于半导体二极管中的 I-V 响应。ICR 现象在微纳流控学（例如生物传感器和芯片实验室应用）中有多种潜在应用。从生物应用的角度来看，大多数生物流体（例如血液、唾液、粘液等）表现出非牛顿粘性弹性行为；它们的流变性质与牛顿流体不同。因此，所得流场应该显示出对粘性弹性流体的流变材料特性的额外依赖，例如流体松弛时间 [Formula: see text] 和流体伸展性 [Formula: see text]。尽管有许多潜在的应用，但对流体的粘弹性行为对离子浓度分布和 ICR 现象的综合影响尚未进行研究。当长度尺度和 Debye 层厚度接近同一数量级时，就会发生 ICR 现象。因此，这项工作广泛研究了在单个圆锥形纳米孔中，粘弹性对流动和离子传质以及 ICR 现象的影响。已经求解了泊松-纳斯特-普朗克（P-N-P）模型与动量方程的广泛组合，以适应多种条件，例如，德拜数 [Formula: see text]，[Formula: see text]，Debye 长度参数 [Formula: see text]，流体伸展性参数 [Formula: see text]，施加的电场强度 [Formula: see text]，表面电荷密度 [Formula: see text]和 [Formula: see text]。为了展示非牛顿流体行为相对于牛顿流体行为的有效性，还显示了牛顿流体的有限结果 ([Formula: see text]，和 [Formula: see text])。在这里研究了圆锥形纳米孔中电渗流 (EOF) 的四个独特的新特征，即：（1）粘弹性流体中的流场和速度分布的详细结构；（2）德拜数和流体伸展性参数对离子电流整流 (ICR) 的影响；（3）作为德拜数和流体伸展性参数函数的体积流量计算；（4）粘弹性参数对纳米孔中离子浓度分布的影响。在高施加电压下，伸展性参数和德拜数都有利于 ICR 现象。此外，在 [Formula: see text] 值较低时，比 [Formula: see text] 值较高时观察到 ICR 现象更为明显。这种效应是由于在 [Formula: see text] 值较低时，电双层的重叠。
