Trapping and chaining self-assembly of colloidal polystyrene particles over a floating electrode by using combined induced-charge electroosmosis and attractive dipole-dipole interactions
Trapping and chaining self-assembly of colloidal polystyrene particles over a floating electrode by using combined induced-charge electroosmosis and attractive dipole-dipole interactions
复制标题
利用组合感应电荷电渗和吸引偶极-偶极相互作用在浮动电极上捕获和链接胶体聚苯乙烯颗粒的自组装
DOI：
10.1039/c5sm01063b
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发表时间：
2015-01-01
期刊：
影响因子：
3.4
通讯作者：
Ren, Yukun
中科院分区：
文献类型：
--
作者：
Liu, Weiyu;Shao, Jinyou;Ren, Yukun
基于诱导电荷电渗流（ICEO）流和偶极-偶极链现象，我们提出了一种新型低频策略，将浮力速度较小的10 mm胶体聚苯乙烯（PS）颗粒捕获在浮动电极表面。对于5-50 Hz的场频率，远低于倒数RC时间尺度，双层极化使电场线围绕理想可极化浮置电极的“绝缘”表面通过。一旦长距离ICEO对流微涡旋将颗粒从主体流体快速输送到电极表面，则沿局部水平电场沿着排列的相邻颗粒通过吸引偶极相互作用彼此吸引，并形成几乎与所施加的电场平行的颗粒链阵列。最重要的是，这种低频捕获方法利用介电泳（DEP）颗粒-颗粒相互作用来增强这种偶极链组装结构的向下浮力，以克服向上的ICEO流体阻力，并在流动停滞区域周围实现稳定的颗粒捕获。为了比较，场频率进一步提高到远高于DC极限。在200 Hz-2 kHz的中频下，这种捕获方法不能工作，因为法向电场分量从导电电极表面发出。此外，在高场频率（43 kHz）下，颗粒可以再次被有效地捕获在电极中心，尽管在电极表面上具有紧凑（3 kHz）或无序（10 kHz）的2D堆积状态，并且主要由短程负DEP力场控制，导致需要长得多的捕获时间。为了更好地解释实验中观察到的各种粒子行为，我们开发了一个理论框架，该框架考虑了粒子/电解质界面处的Maxwell-Wagner界面电荷弛豫和电极/电解质界面处的场致双层极化，并将其应用于量化粒子-粒子电动相互作用。通过这种简单的几何结构的浮动电极，我们的研究结果提供了一种新的方式来实现捕获的胶体粒子与一个小的浮力速度下的ICEO流和吸引偶极-偶极相互作用的联合作用。
We propose a novel low-frequency strategy to trap 10 mm colloidal polystyrene (PS) particles of small buoyancy velocity on the surface of a floating electrode, on the basis of combined induced-charge electroosmotic (ICEO) flow and dipole-dipole chaining phenomenon. For field frequencies of 5-50 Hz, much lower than the reciprocal RC time scale, double-layer polarization makes electric field lines pass around the 'insulating' surface of the ideally polarizable floating electrode. Once the long-range ICEO convective micro-vortexes transport particles quickly from the bulk fluid to the electrode surface, neighbouring particles aligned along the local horizontal electric field attract one another by attractive dipolar interactions, and form arrays of particle chains that are almost parallel with the applied electric field. Most importantly, this low-frequency trapping method takes advantage of the dielectrophoretic (DEP) particle-particle interaction to enhance the downward buoyancy force of this dipolar chaining assembly structure, in order to overcome the upward ICEO fluidic drag and realize stable particle trapping around the flow stagnation region. For the sake of comparison, the field frequency is further raised far above the DC limit. At the intermediate frequencies of 200 Hz-2 kHz, this trapping method fails to work, since the normal electric field component emanates from the conducting electrode surface. Besides, at high field frequencies (43 kHz), particles can be once again effectively trapped at the electrode center, though with a compact (3 kHz) or disordered (10 kHz) 2D packing state on the electrode surface and mainly governed by the short-range negative DEP force field, resulting in requiring a much longer trapping time. To gain a better interpretation of the various particle behaviours observed in experiments, we develop a theoretical framework that takes into account both Maxwell-Wagner interfacial charge relaxation at the particle/electrolyte interface and the field-induced double-layer polarization at the electrode/electrolyte interface, and apply it to quantify the particle-particle electrokinetic interactions. With this simple geometrical configuration of a floating electrode, our results provide a new way to realize trapping of colloidal particles with a small buoyancy velocity under the combined action of ICEO flow and an attractive dipole-dipole interaction.