论文标题
由表面声波诱导的小型通道中的电流流动
Electroosmotic flow in small-scale channels induced by surface-acoustic waves
论文作者
论文摘要
使用Navier-Stokes，Nernst-Planck和Poisson方程的数值模拟来描述平行板纳米渠道中水溶液中的传输过程，在该纳米通道中，地表声波（SAWS）沿着（piezo-Active）通道壁上站立或行进。已经发现，除了传统的声流流外，还诱发了时间平均的电流动流。采用流函数涡流配方，显示出麦克斯韦的应力项会导致电渗推进，该电源推进与在交流电流（AC）电流（EOF）的背景下在质量上相同。差异主要是由于锯的高致动频率，该锯在MHz范围内，而不是在ACEOF的典型的KHz状态中。此外，EOF在SAW的行进方向上的瞬时空间周期性与后者的分散关系而不是自由几何参数本质上链接。这导致特定的频带，其中可以找到相当大的幅度。在低频端，电动双层（EDL）厚度与锯波长之间的比率变得极小，从而使导致非散布时间平均流量的净力同样小。在高频端，EDL的RC时间比锯频率的倒数大得多，导致EDL的有效电荷密度消失。对于平行板通道，可以通过在两个具有相同频率但相移$ 180^\ circ $相移的通道壁上使用两个锯来最大化EOF。看来锯eof是这种情况的主要抽水机制。提出的驱动可能是通过狭窄的导管和通道驱动液体电解质的可行替代方法，而无需电气互连和电极。
Numerical simulations of the Navier-Stokes, Nernst-Planck, and the Poisson equations are employed to describe the transport processes in an aqueous electrolyte in a parallel-plate nanochannel, where surface-acoustic waves (SAWs) are standing or traveling along (piezo-active) channel walls. It is found that -- in addition to the conventional acoustic streaming flow -- a time-averaged electroosmotic flow is induced. Employing the stream function-vorticity formulation, it is shown that the Maxwell stress term causes an electroosmotic propulsion that is qualitatively identical to the one discussed in the context of alternating current (AC) electroosmosis (EOF). Differences arise mainly due to the high actuation frequencies of SAWs, which are in the MHz range rather than in the kHz regime typical for ACEOF. Moreover, the instantaneous spatial periodicity of the EOF in the travel direction of the SAW is intrinsically linked to the dispersion relation of the latter rather than a free geometric parameter. This leads to a specific frequency band where an EOF of sizable magnitude can be found. On the low frequency end, the ratio between the electric double layer (EDL) thickness and the SAW wavelength becomes extremely small so that the net force leading to a non-vanishing time-averaged flow becomes equally small. On the high frequency end, the RC time of the EDL is much larger than the inverse of the SAW frequency leading to a vanishing effective charge density of the EDL. For a parallel-plate channel, the EOF can be maximized by using two SAWs on both channel walls that have the same frequency but are phase-shifted by $180^\circ$. It appears that the SAW-EOF is the dominant pumping mechanism for such a scenario. The proposed actuation might be a viable alternative for driving liquid electrolytes through narrow ducts and channels, without the need for electric interconnects and electrodes.
