Liquid Crystal Order in Colloidal Suspensions of Spheroidal Particles by Direct Current Electric Field Assembly

Abstract

D C 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. Rapid assembly of anisotropic colloidal particles is essential to create complex, uniform, and scalable crystal structures for applications. In this study, DC electric fields are used to accelerate the self‐assembly process of spheroidal particles. The image shows confocal microscopy images and renderings from image processing of the field‐induced 3D ordering. The assembly is shown to have high‐quality orientational order and previously unobserved periodic and dense layered ordering.