(477e) Magnetic Control over Dynamic Clustering of Colloids

Understanding the arrangement of individual building blocks in response to changes in the free energy available is a challenge of non-equilibrium matter. The push-and-pull balance between ordered and disordered states has been described by a ratio of attraction and repulsion, yet no experimental demonstration with a dynamic energy landscape is available. Here, we uncover the ‘dual nature’ of ferrofluids, particulate and continuous, to design a colloidal platform that couples competitive interactions with non-equilibrium dynamics. Using a binary suspension of microspheres in ferrofluid, we describe cyclical order-disorder-order transitions, and we access a dynamic cluster state. We show that crystal and fluid states represent two extremes in the competition between attraction and repulsion, while arrangement into clusters is a pseudo-equilibrium only observed from the true balance of interaction forces.