目的:电场驱动的活性颗粒系统中的对称破坏可以通过施加空间均匀的,但是时间上不均匀,交流(AC)信号。无论暴露于锯齿AC信号的粒子类型如何,离子电荷层的不均匀感应极化导致主动推进的主要电流体动力效应,称为不对称场电泳(AFEP)。
方法:含有三种尺寸乳胶微球的悬浮液,以及Janus和金属涂层颗粒受到不同电压的锯齿交流信号,频率,和时间不对称。通过显微镜进行的颗粒跟踪用于分析其作为关键参数的函数的运动性。
结果:粒子表现出场共线主动推进,并且AC信号的时间反转导致它们的运动方向的反转。实验速度数据作为场强的函数,频率,和信号不对称性由非对称离子浓差极化模型支持。粒子迁移的方向在低频域中表现出与尺寸相关的交叉。这使得能够实现简单且有效的片上分选的新方法。将AFEP与其他AC运动机制相结合,如感应电荷电泳,允许对粒子运动进行多轴控制,并且可以开发新颖的交流场驱动有源微系统。
OBJECTIVE: Symmetry breaking in an electric field-driven active particle system can be induced by applying a spatially uniform, but temporally non-uniform, alternating current (AC) signal. Regardless of the type of particles exposed to sawtooth AC signals, the unevenly induced polarization of the ionic charge layer leads to a major electrohydrodynamic effect of active propulsion, termed Asymmetric Field Electrophoresis (AFEP).
METHODS: Suspensions containing latex microspheres of three sizes, as well as Janus and metal-coated particles were subjected to sawtooth AC signals of varying voltages, frequencies, and time asymmetries. Particle tracking via microscopy was used to analyze their motility as a function of the key parameters.
RESULTS: The particles exhibit field-colinear active propulsion, and the temporal reversal of the AC signal results in a reversal of their direction of motion. The experimental velocity data as a function of field strength, frequency, and signal asymmetry are supported by models of asymmetric ionic concentration-polarization. The direction of particle migration exhibits a size-dependent crossover in the low frequency domain. This enables new approaches for simple and efficient on-chip sorting. Combining AFEP with other AC motility mechanisms, such as induced-charge electrophoresis, allows multiaxial control of particle motion and could enable development of novel AC field-driven active microsystems.