Berlin 2005 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 22: Colloids
CPP 22.2: Talk
Tuesday, March 8, 2005, 11:30–11:45, TU C243
Equation of state of polyelectrolyte multilayer- coated colloids — •Monique Dubois1, Annette Meister2, Monika Schönhoff1,3, Thomas Zemb2, and Helmuth Möhwald1 — 1Max-Planck-Institut für Kolloid- und Grenzflächenforschung, D-14424 Potsdam/Golm — 2LIONS, DRECAM/SCM, Bat 125, CEA Saclay, F-91191 Gif sur Yvette Cedex — 3Institut für Physikalische Chemie, WWU Münster, Corrensstr.30, D-48149 Münster
Establishing the equation of state means establishing the relation between osmotic pressure (water activity), temperature and density in a fluid. This method is the most general way to measure the interaction potential between colloids without artefacts. We establish here for the first time a full equation of state for polyelectrolyte- coated colloids. Coated colloids prepared with six and seven polyelectrolyte layers, respectively, are equilibrated under osmotic stress, via dialysis equilibrium in the absence of added salt. Interparticle distances are analysed by USAXS and chemical analysis. We show in this report that three regimes can be clearly distinguished in the equation of state: a gravitational regime, an expanded brush regime and an interpenetrating brush regime, with the terminating layer acting as an extended brush. Physical origins of these three distinct regimes are discussed in the context of corresponding electrostatic models taking into account the brush repulsion and counterion pressure contributions.