(458e) Colloidal Molecules Assembled from Binary Spheres Under an AC Electric Field

Colloidal particles are often used as analogues for simple atoms and molecules, however these systems typically lack the complexities present in their counterparts. Here we report the assembly of colloidal molecules from a binary mixture of spheres (1, 1.6, 2, and 4 µm) under an alternating current electric field. The assembled oligomers typically consist of a large sphere in the center and a number of smaller satellite spheres surrounding the large one. In deionized water, the number of satellite particles (i.e., the coordination number) increases with increasing size ratio of the constituent particles. For a given binary mixture, the oligomer coordination number decreases with increasing frequency of the applied field. These trends can be correctly captured by computing the electrostatic energy of the systems based on induced dipolar interactions. By suspending the particles in polyvinylpyrrolidone (PVP) aqueous solution, we can further tune the bond length of the oligomers independently from their coordination numbers. The addition of PVP also allows us to fix the assembled colloidal molecules permanently so that they stay intact even after the electric field is turned off. Our method provides a robust way to produce a family of colloidal molecules with controllable geometry.