离子浓度极化引起的微涡旋动力学
Dynamics of microvortices induced by ion concentration polarization
摘要：
我们研究了电渗析系统的局部流体动力学和全局电响应的耦合动力学，该系统由邻近电荷选择性膜的电解质溶液组成。在DC电流下，抗衡离子通过带电膜传输，同时共离子的通过受到限制，从而形成离子浓差极化（ICP）或梯度。在足够大的电流，电压降和流场的同时测量揭示了几个不同的动态制度。最初，电渗析系统显示稳定的欧姆电压差（$ΔV_{ohm}$），随后是恒定的电压跳变（$ΔV_c$）。在该电压增加之后，微涡旋立即设置并且随着时间的推移在尺寸和速度上都增长。在这种增长之后，所产生的电压在固定值附近稳定下来。平均涡流尺寸和速度也稳定，而单个涡流变得不稳定和动态。这些定量结果表明，微涡旋会产生过量电压降（高于$ΔV_{ohm} + ΔV_c$）并维持大致恒定的电导率，从而破坏初始ICP，同时粘性耗散显着降低。
英文摘要：
We investigate the coupled dynamics of the local hydrodynamics and global electric response of an electrodialysis system, which consists of an electrolyte solution adjacent to a charge selective membrane under electric forcing. Under a DC electric current, counterions transport through the charged membrane while the passage of co-ions is restricted, thereby developing ion concentration polarization (ICP) or gradients. At sufficiently large currents, simultaneous measurements of voltage drop and flow field reveal several distinct dynamic regimes. Initially, the electrodialysis system displays a steady Ohmic voltage difference ($ΔV_{ohm}$), followed by a constant voltage jump ($ΔV_c$). Immediately after this voltage increase, micro-vortices set in and grow both in size and speed with time. After this growth, the resultant voltage levels off around a fixed value. The average vortex size and speed stabilize as well, while the individual vortices become unsteady and dynamic. These quantitative results reveal that micro-vortices set in with an excess voltage drop (above $ΔV_{ohm} + ΔV_c$) and sustain an approximately constant electrical conductivity, destroying the initial ICP with significantly low viscous dissipation.
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