Interfacial Stability in Tensionless Phase-Separated Quorum-Sensing Systems

Interfacial phenomena of motility-induced phase separation of active particles challenge our conventional understanding of phase coexistence. Despite the ubiquity of nonmechanical communication couplings among real active particles, most works on active interface have concentrated on active Brownian systems with steric interparticle interactions. Here, we study the interfacial behavior of phase-separated active particles interacting solely via quorum-sensing communications using both theory and simulations. Strikingly, we find that the quorum-sensing active system exhibits vanishing mechanical surface tension but nonzero effective capillary surface tension. We further demonstrate that the mechanical equilibrium of the tensionless interface is sustained by polarization force at the interface; while its dynamics is governed by the surface stiffness, which arises from tangential particle flux induced by local interfacial deformation. Our work reveals the fundamental distinction between mechanical and capillary surface tensions in active matter and paves the way for future exploration of active interface phenomena.