Berlin 2001 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 18: Poster: Polymer Blends, Heterogeneous Systems, Colloids and Nanoparticles, Interfaces, Polyelectrolytes

CPP 18.15: Poster

Wednesday, April 4, 2001, 12:30–15:00, AT1

Complex interactions in concentrated Microgel - Dispersions — •Thomas Eckert, Thorsten Scherer, and Eckhard Bartsch — Universität Mainz, Jakob-Welder-Weg 15, 55099 Mainz

The interaction potential of microgel colloids swollen in a good solvent is determined by the internal architecture: the compressibility of the polymer network defines the steepness of the repulsive interactions while the length of the dangling ends on the surface determines the range of interactions. Thus one expects a systematic increase of the softness of interactions when decreasing the crosslink density. To test this hypothesis we have studied the phase behavior, the static structure factor and the rheological behavior of these particles up to high volume fractions. We find that the phase behavior and the static structure factor do not allow to discriminate between 1:10 and 1:50 crosslinked microgels. Extracting the exponents of an inverse power potential from the volume fraction dependence of the plateau modulus we find exponents of 22 and 12 for 1:10 and 1:50 crosslinked microgels, respectively. A possible explanation for these contradictory results is the presence of free polymer, hidden in the colloids due to imperfect crosslinking. This free polymer may leave the particles in a good solvent, thereby inducing depletion forces. These depletion forces could counteract the effect of the decreasing crosslink density on the effective interaction potential.