8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Thu 811:10-14:00P7.25Ion specificity and the theory of stability of colloidalsuspensionsAlexandre P. dos Santos 1 and Yan Levin 11 Universidade Federal do Rio grande do Sul, Av. Bento Gonçalves 9500, 15051,Porto Alegre, BrazilA theory is presented which allow us to accurately calculate the critical coagulation concentration(CCC) of hydrophobic colloidal suspensions. For positively charged particles the CCC’s follow theHofmeister (lyotropic) series. For negatively charged particles the series is reversed. We find thatstrongly polarizable chaotropic anions are driven towards the colloidal surface by electrostatic andhydrophobic forces. Within approximately one ionic radius from the surface, the chaotropic anionsloose part of their hydration sheath and become strongly adsorbed. The kosmotropic anions, onthe other hand, are repelled from the hydrophobic surface. The theory is quantitatively accuratewithout any adjustable parameters. We speculate that the same mechanism is responsible for theHofmeister series that governs stability of protein solutions.25