Self-Propulsion via Nontransitive Phase Coexistence in Chemically Active Mixtures

Chemical activity is central in active matter, where local fuel consumption can lead to self-propulsion and phase separation. However, phase separation can also originate from passive physical interactions. To understand the influence of chemical activity on phase separation, we study mixtures where solvent species interconvert while solutes segregate. We demonstrate that such reactions affect phase separation by altering the chemical potential balance and by introducing an osmotic pressure difference at interfaces. However, the system does not permit a pseudopressure balance, and bulk compositions depend on which phases are in contact. Consequently, phase coexistence is no longer transitive, which enables self-propulsion and more complex dynamics.