Directed assembly of Janus particles under high frequency ac-electric fields: effects of medium conductivity and colloidal surface chemistry.
Directed assembly of Janus particles under high frequency ac-electric fields: effects of medium conductivity and colloidal surface chemistry.
复制标题
高频交流电场下 Janus 粒子的定向组装：介质电导率和胶体表面化学的影响。
作者：
Lu Zhang;Yingxi Zhu
通过原位显微镜观察，实验研究了高频非均匀交流电场下聚苯乙烯基Janus颗粒在半球形颗粒表面上的操纵和组装。交流场频率，介质电导率，和粒子表面化学的Janus胶体组装体的结构上的强烈影响进行了观察。在低电导率（σ（m）从0.0007 S/m到0.0153 S/m）下，在25 kHz到20 MHz的交流频率范围内观察到Janus粒子的珍珠链，表明介电泳（DEP）引导的组装。相反，Janus粒子的链在高σ（m）（0.0153 ~ 0.116 S/m）的一定频率范围内被破坏，这表明诱导电荷电泳（ICEP）和DEP的联合作用。实验测定了分形聚集在高σ（m）（0.0153 ~ 0.116 S/m）时的临界跃迁频率，与理论预测的ICEP频率上限值吻合较好。此外，它表明，通过使用两性离子Janus粒子，在AC场下的Janus粒子的组装结构可以通过在Janus粒子的每个半球表面上的化学涂层来修改。
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.