Understanding the arrangement of matter under non-equilibrium conditions is a grand challenge in thermodynamics. The push-and-pull balance between ordered and disordered states has been theoretically described by a ratio of attraction and repulsion, yet its experimental validity is ambiguous. Here, we uncover the <i>dual nature</i> 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 dynamic cluster states. 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. Our findings establish a platform for experimental modeling of living matter with tunable competition between equilibrium and non-equilibrium forces.

Dynamic and competitive interactions via the dual nature of ferrofluids

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.