Chanda Sourayon, Tsai Peichun Amy
Department of Mechanical Engineering, University of Alberta, 9211 116 St. NW, Edmonton, AB T6G 1H9, Canada.
Membranes (Basel). 2022 Apr 29;12(5):481. doi: 10.3390/membranes12050481.
Diffusioosmosis concerns ionic flow driven by a concentration difference in a charged nano-confinement and has significant applications in micro/nano-fluidics because of its nonlinear current-voltage response, thereby acting as an active electric gating. We carry out a comprehensive computation fluid dynamics simulation to investigate diffusioosmotic flow in a charged nanochannel of linearly varying height under an electrolyte concentration gradient. We analyze the effects of cone angle (α), nanochannel length () and tip diameter (dt), concentration difference (Δc = 0-1 mM), and external flow on the diffusioosmotic velocity in a tapered nanochannel with a constant surface charge density (σ). External flow velocity (varied over five orders of magnitude) shows a negligible influence on the diffusioosmotic flow inside the tapered nanochannel. We observed that a cone angle causes diffusioosmotic flow to move towards the direction of increasing gap thickness because of stronger local electric field caused by the overlapping of electric double layers near the smaller orifice. Moreover, the magnitude of average nanoflow velocity increases with increasing |α|. Flow velocity at the nanochannel tip increases when dt is smaller or when is greater. In addition, the magnitude of diffusioosmotic velocity increases with increasing Δc. Our numerical results demonstrate the nonlinear dependence of tapered, diffusioosmotic flow on various crucial control parameters, e.g., concentration difference, cone angle, tip diameter, and nanochannel length, whereas an insignificant relationship on flow rate in the low Peclet number regime is observed.
扩散渗透涉及由带电纳米限域内的浓度差驱动的离子流，由于其非线性电流 - 电压响应，在微纳流体中具有重要应用，从而可作为一种有源电门控。我们进行了全面的计算流体动力学模拟，以研究在电解质浓度梯度下，高度线性变化的带电纳米通道中的扩散渗透流。我们分析了锥角（α）、纳米通道长度（）和尖端直径（dt）、浓度差（Δc = 0 - 1 mM）以及外部流对具有恒定表面电荷密度（σ）的锥形纳米通道中扩散渗透速度的影响。外部流速（在五个数量级范围内变化）对锥形纳米通道内的扩散渗透流影响可忽略不计。我们观察到，由于小孔附近电双层重叠导致的更强局部电场，锥角会使扩散渗透流朝着间隙厚度增加的方向移动。此外，平均纳米流速的大小随|α|的增加而增加。当dt较小时或 较大时，纳米通道尖端的流速会增加。此外，扩散渗透速度的大小随Δc的增加而增加。我们的数值结果表明，锥形扩散渗透流对各种关键控制参数（如浓度差、锥角、尖端直径和纳米通道长度）具有非线性依赖性，而在低佩克莱数 regime 中观察到其与流速的关系不显著。
