Berlin 2012 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 8: Glasses I (with CPP, talks by CPP)
DY 8.4: Vortrag
Montag, 26. März 2012, 16:15–16:30, C 243
Effect of cross-link density on re-entrant melting of microgel colloids — •Malte Wiemann1, Norbert Willenbacher2, and Eckhard Bartsch1,3 — 1University of Freiburg, Department of Physical Chemistry, Freiburg, Germany — 2Karlsruhe Institute of Technology, Department of Mechanical Process Engineering and Mechanics, Karlsruhe, Germany — 3University of Freiburg, Department of Macromolecular Chemistry, Freiburg, Germany
Fluid states of colloidal dispersions at volume fractions above the glass transition can be accessed by introducing short-ranged depletion attraction [1]. For a binary mixture of PS-microgel particles (cross-linking density 1:50) in a good organic solvent DLS-measurements revealed a fluidization up to a volume fraction φ=0.69 when linear non-adsorbing polymer is added. The high packing fraction up to which fluid states could be observed raised the question whether the magnitude of this effect is a specialty of the microgel system. We prepared microgels with a much higher crosslinking density (1:10) which should be a good approximation of hard sphere colloids. Fluid states could again be obtained above φg, however, up to a significantly smaller packing fraction. The amount of free polymer needed to fluidize the dispersion was much lower as compared to the previous mixture [2]. The existence of fluid states up to high volume fractions for the 1:50 crosslinked particles is - at least partially - a microgel effect which is at present not fully understood and possible origins will be discussed. [1] K. Dawson etal., Phys. Rev. E 63, 011401 (2000) [2] M. Wiemann, N. Willenbacher, E. Bartsch, Colloid Surface A, 10.1016/j.colsurfa.2011.11.029