Directed Assembly of Janus Particles under High Frequency ac-Electric Fields: Effects of Medium Conductivity and Colloidal Surface Chemistry

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• 作者：Lu Zhang ; Yingxi Zhu
• 刊名：Langmuir
• 出版年：2012
• 出版时间：September 18, 2012
• 年：2012
• 卷：28
• 期：37
• 页码：13201-13207
• 全文大小：563K
• 年卷期：v.28,no.37(September 18, 2012)
• ISSN：1520-5827

文摘

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, 蟽_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 蟽_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 蟽_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.