Program of Macromolecular Science and Engineering, University of Michigan, Ann Arbor, MI, USA.
Small. 2012 May 21;8(10):1551-62. doi: 10.1002/smll.201102265. Epub 2012 Mar 1.
DC electric fields are used to produce colloidal assemblies with orientational and layered positional order from a dilute suspension of spheroidal particles. These 3D assemblies, which can be visualized in situ by confocal microscopy, are achieved in short time spans (t < 1 h) by the application of a constant voltage across the capacitor-like device. This method yields denser and more ordered assemblies than had been previously reported with other assembly methods. Structures with a high degree of orientational order as well as layered positional order normal to the electrode surface are observed. These colloidal structures are explained as a consequence of electrophoretic deposition and field-assisted assembly. The interplay between the deposition rate and the rotational Brownian motion is found to be critical for the optimal ordering, which occurs when these rates, as quantified by the Peclet number, are of order one. The results suggest that the mechanism leading to ordering is equilibrium self-assembly but with kinetics dramatically accelerated by the application of the DC electric field. Finally, the crystalline symmetry of the densest structure formed is determined and compared with previously studied spheroidal assemblies.
直流电场用于从各向同性的稀悬胶体中产生具有取向和层状位置有序的胶体组装体。通过在电容器状装置上施加恒压，可以在短时间内（t < 1 h）实现这些可以通过共焦显微镜原位可视化的 3D 组装体。与其他组装方法相比，该方法产生的组装体更密集、更有序。观察到具有高取向有序度以及与电极表面垂直的层状位置有序的结构。这些胶体结构被解释为电泳沉积和场辅助组装的结果。发现沉积速率和旋转布朗运动之间的相互作用对于最佳有序排列至关重要，当这些速率（如 Peclet 数所量化的）为数量级时，就会发生最佳有序排列。结果表明，导致有序的机制是平衡自组装，但通过施加直流电场，动力学得到了显著加速。最后，确定了形成的最密集结构的晶体对称性，并与以前研究过的各向同性胶体组装体进行了比较。
