We present a novel method to tune the interaction potential from 5kBT to 40kBT in situ between micron-sized superparamagnetic colloids. The potential is composed of a highly tunable long-range attraction induced via a rotating magnetic field and a short-range electrostatic repulsion. Various 2-D thermodynamic phases are observed in a colloidal suspension at different field strengths. Quantitative agreement is found between theory and experiments for dipolar interactions. A theory to account for the induced dipole due to neighboring particles is also presented. The effective three-body potential of a dilute trimer system is measured to account for many-body effects in the system. These results demonstrate an ideal model to study the phase behavior in 2-D systems.
Du, Di, Dichuan Li, Madhuri Thakur, Sibani Lisa Biswal