Stability and liquid-liquid phase separation in mixed lipid bilayers Gabriel S. Longo § , M. Schick † and I. Szleifer *1 § International School for Advanced Studies via Beirut 2-4, 34014 Trieste, Italy and The Abdus Salam International Centre for Theoretical Physics Strada Costiera 11, 34014 Trieste, Italy † Department of Physics, University of Washington, Seattle, WA 98195-1560 * Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208 January 5, 2009 1 Corresponding author. Address: Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, U.S.A., Tel.: (847) 467-0674 Fax: (847) 491-4928, e-mail: igalsz@northwestern.edu