290568 Assembly of Anisotropic Particles Under Electric Fields

Tuesday, October 30, 2012
Hall B (Convention Center )
Fuduo Ma, Sijia Wang and Ning Wu, Chemical & Biological Engineering Department, Colorado School of Mines, Golden, CO

Anisotropic colloids can possess anisotropic properties in geometry, chemical composition or surface functionality. As such, they can recognize each other and assemble via directional interactions. By tuning the directional interactions between particles, anisotropic particles can assemble into diversified types of crystalline and non-crystalline structures. This poster will focus on the electric-field directed assembly of two types of anisotropic particles -rigid dimers and flexible trimers under electric fields.

For colloidal dimers with rigid bonds, we recently observed rich patterns in both crystalline and non-crystalline forms, such as clusters with chiraities, and dimer crystals with alternating orientations, which depend on the anisotropies in geometry and surface charges. Our modeling demonstrated that the competition and balance between electrostatic interactions and electrohydrodynamic interactions bring a variety of phases and assembly pathways between dimers. The close-packed crystal of dimers provides promise for fabricating three-dimensional photonic crystals based on non-spherical particles.

In addition, we have investigated colloidal trimers with flexible bonds, assembled from spherical colloids under electric fields. At low particle and salt concentrations, we observed a family of well-defined clusters ranging from 3 to 9 particles, with non-trivial high populations for trimers, tetramers, hexamers, and nonamers. At higher particle and salt concentrations, the colloidal clusters with flexible angles can further assemble and connect themselves into several hierarchical structures, including non-close-packed networks that have not been observed before. The dynamic assembly process of colloids resembles the chemical reactions between real molecules, which could open a new realm for making complex “colloidal molecules” from simple particles with prescribed assembly pathways.

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