Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA.
Langmuir. 2012 Sep 18;28(37):13201-7. doi: 10.1021/la302725v. Epub 2012 Sep 7.
The manipulation and assembly of polystyrene-based Janus particles of varied surface chemistry on one hemispherical particle surface under high frequency nonuniform ac-electric fields is examined experimentally by in situ microscopic observation. Strong effects of ac-field frequency, medium conductivity, and particle surface chemistry on the structure of Janus colloidal assembly are observed. At low medium conductivity, σ(m) from 0.0007 S/m to 0.0153 S/m, pearl chains of Janus particles are observed over the ac-frequency range from 25 kHz to 20 MHz, indicating the dielectrophoresis (DEP)-directed assembly. In contrast, the chaining of Janus particles is disrupted in a certain frequency range at high σ(m) from 0.0153 S/m to 0.116 S/m, suggesting the combining effects of both induced-charge electrophoresis (ICEP) and DEP. The critical transition frequency for the onset of the fractal aggregation at high σ(m) from 0.0153 S/m to 0.116 S/m is experimentally determined, showing a good agreement with the theoretically predicted upper ICEP frequency limit. Additionally, it is demonstrated that by using zwitterionic Janus particles, the assembled structure of Janus particles under ac-fields can be modified by the chemical coatings on each hemispherical surface of Janus particles.
在高频非均匀交流电场下，通过原位微观观察实验研究了在一个半球形粒子表面上对具有不同表面化学性质的聚苯乙烯基 Janus 粒子进行操纵和组装。观察到交流场频率、介质电导率和粒子表面化学对 Janus 胶体组装结构的强烈影响。在低电导率介质中，σ(m) 从 0.0007 S/m 到 0.0153 S/m，在 25 kHz 到 20 MHz 的交流频率范围内观察到 Janus 粒子的珍珠链，表明了介电泳（DEP）引导的组装。相比之下，在高电导率介质中（σ(m) 从 0.0153 S/m 到 0.116 S/m），在一定频率范围内，Janus 粒子的链状结构被破坏，这表明了诱导电荷电泳（ICEP）和 DEP 的联合作用。在高电导率介质中（σ(m) 从 0.0153 S/m 到 0.116 S/m），实验确定了分形聚集起始的临界转变频率，与理论预测的 ICEP 上限频率吻合较好。此外，还证明了通过使用两性离子 Janus 粒子，可以通过 Janus 粒子每个半球形表面的化学涂层来修饰在交流场下 Janus 粒子的组装结构。
