Department of Chemical and Biomolecular Engineering, Johns Hopkins University, 221 Maryland Hall, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
Phys Rev Lett. 2012 Nov 2;109(18):187602. doi: 10.1103/PhysRevLett.109.187602. Epub 2012 Oct 31.
We demonstrate a new type of alternating current (ac) interfacial polarization and frequency-dependent fluid displacement phenomenon at a liquid-liquid electrical interface. Two fluid streams--one with a greater electrical conductivity and the other a greater dielectric constant--are made to flow side by side in a microfluidic channel. An ac electric field is applied perpendicular to the interface formed between the liquid lamellae, and fluid is observed to displace across the liquid-liquid interface. The direction and magnitude of this displacement is frequency dependent. At low ac frequency, below the interfacial inverse charge relaxation time, the high-conductivity fluid displaces into the high-dielectric stream. At high frequency the direction of liquid displacement reverses, and the high-dielectric stream injects into the high-conductivity stream. The interfacial crossover frequency where the liquid displacement direction reverses is dependent on differences in electrical properties between the two fluid streams, and is well explained by Maxwell-Wagner polarization mechanics.
我们在液-液电界面展示了一种新型的交流（ac）界面极化和频率相关的流体置换现象。两种具有不同电导率和介电常数的流体在微流道中并排流动。交流电场垂直于液膜之间形成的界面施加，观察到流体在液-液界面上置换。这种置换的方向和幅度是频率相关的。在低于界面反电荷弛豫时间的低频下，高电导率流体置换到高介电流中。在高频下，液体置换的方向反转，高介电流注入高电导率流。液体置换方向反转的界面交叉频率取决于两种流体之间的电特性差异，并且很好地解释了 Maxwell-Wagner 极化力学。
