Berlin 2008 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 1: DRG-DPG SYMPOSIUM Rheology I

CPP 1.1: Hauptvortrag

Montag, 25. Februar 2008, 09:30–10:00, C 130

Multiple glassy states and mechanics of soft colloids — •Dimitris Vlassopoulos — FORTH and Univ. of Crete, Hereklion, Greece

Colloidal glass transition and its manipulation represent a topic of ever increasing scientific interest. Hard sphere colloids and more recently their mixtures with linear non-adsorbing polymers has been the systems most frequently studied. Perhaps the most interesting recent observation is the melting of a (repulsive) glass upon adding polymer depletant, and the transition into a re-entrant different (attractive) glass upon further increasing the strength of depletion. Here, we are interested in changing the pair interaction potential. In particular, we use colloidal star polymers, a model system with ultrasoft interactions. We study their vitrification under different conditions: temperature-dependent solvent, mixtures with linear chains and binary asymmetric star mixtures. We find a wide range of glass transitions, which we try to rationalize by invoking the cage picture and with support from mode coupling theory. We demonstrate to power of rheology to act both as a sensitive detection tool and as a means of inducing structural changes. Concerning the former, the data are summarized in terms of kinetic state diagrams. For the latter, we present the phenomenology of yielding of the star glasses and suggest possible connections to aging. The main outcome is, we believe, an enhanced ability to tailor the flow of glassy suspensions of soft particles. In collaboration with E. Stiakakis, G. Petekidis, C. N .Likos, C. Mayer, E. Zaccarelli, F. Sciortino, M. Helgeson, N. J. Wagner, H. Iatrou, N. Hadjichristidis.