Pressure and Phase Equilibria in Interacting Active Brownian Spheres

• Main Authors: Solon, Alexandre P. (Author), Stenhammar, Joakim (Author), Wittkowski, Raphael (Author), Kardar, Mehran (Contributor), Kafri, Yariv (Author), Cates, Michael E. (Author), Tailleur, Julien (Author)
• Other Authors: Massachusetts Institute of Technology. Department of Physics (Contributor)
• Format: Article
• Language: English
• Published: American Physical Society, 2015-05-12T12:21:28Z.
• Subjects: Article
• Online Access: Get fulltext

We derive a microscopic expression for the mechanical pressure P in a system of spherical active Brownian particles at density ρ. Our exact result relates P, defined as the force per unit area on a bounding wall, to bulk correlation functions evaluated far away from the wall. It shows that (i) P(ρ) is a state function, independent of the particle-wall interaction; (ii) interactions contribute two terms to P, one encoding the slow-down that drives motility-induced phase separation, and the other a direct contribution well known for passive systems; and (iii) P is equal in coexisting phases. We discuss the consequences of these results for the motility-induced phase separation of active Brownian particles and show that the densities at coexistence do not satisfy a Maxwell construction on P.
Engineering and Physical Sciences Research Council (Grant EP/J007404)
National Science Foundation (U.S.) (Grant NSF PHY11-25925)