Tuning Higher Order Structure in Colloidal Fluids

Colloidal particles self assemble into a wide range of structures under external AC electric fields due to induced dipolar interactions. As a result of these dipolar interactions, at low volume fraction the system is modulated between a hard–sphere like state (in the case of zero applied field) and a “string fluid” upon application of the field. Using both particle–resolved experiments and computer simulations, we investigate the emergence of the string fluid with a variety of structural measures including two-body and higher– order correlations. The higher–order structure we probe using three-body spatial correlation functions and a many–body approach based on minimum energy clusters of a dipolar–Lennard– Jones system. The latter constitutes a series of geometrically distinct minimum energy clusters upon increasing the strength of the dipolar interaction, which are echoed in the higher–order structure of the colloidal fluids we study here. We find good agreement between experiment and simulation at the two-body level. Higher–order correlations exhibit reasonable agreement between experiment and simulation, again with more discrepancy at higher field strength for three–body correlation functions. At higher field strength, the cluster population in our experiments and simulations is dominated by the minimum energy clusters for all sizes 8 ≤ m ≤ 12.