(112d) Dissipative Self-Assembly of Colloidal Dispersions

Colloids and nanoparticles self-assemble in external fields, a property which enables functional and smart materials like magnetorheological fluids and potentially new ones in which structure controls the transport of heat, light, or chemical species. Suspensions of paramagnetic colloids are a model to study these phenomena. In experiments conducted in the microgravity environment of the International Space Station and earth-based experiments, we find that several factors govern the kinetics of phase separation of paramagnetic colloids and the steady-state structures that they form in periodically toggled fields, including the field strength, toggle frequency, and duty ratio. The suspension structures observed over many toggle cycles are in good agreement with those predicted by the theoretical and computational work of Sherman et al. (Sherman, Z. M.; Rosenthal, H.; Swan, J. W. Langmuir 2018, 34, 1029−1041), including a dependence on the field duty. Our results are important experimental tests for models of dissipative self-assembly, processes in which ordered structures form far from equilibrium by continuously absorbing energy and dissipating it into their surroundings. Such active assembly processes offer promising methods to generate complex structures and circumvent arrest in undesirable metastable states.