Non-reciprocal interactions result in the partial demixing of binary polar fluids

Agents or particles that spontaneously assemble into active liquids can feature non-reciprocal interactions. In this presentation, we investigate the consequences of non-reciprocity on the structure and dynamics of binary mixtures of polar liquids. We assemble colloidal polar liquids, known as Quincke-roller flocks, out of bi-disperse colloidal suspensions. Interestingly, partial demixing occurs spontaneously in the system. We first quantify this macroscopic behaviour and then search for its origin at the particle scale. Finally, we complement our experimental analysis with hydrodynamics theory. We gain insight into the spontaneous demixing process and propose a simplified description of such mixtures by pushing non-reciprocal interactions to the limit of one-way actions. Within this simplified description, one species creates an active environment which, in essence, drives the second species. Our work illustrates the possibility of exploiting non-reciprocity in active materials to achieve precise functions.