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

Wed 711:10-14:00P5.163Depletion attractive microgel suspensions:crystallization, coarsening, segregationThomas Palberg, 1 Anna Kozina, 2 Pedro Diaz-Leyva, 2 Dominik Sagawe, 2 EckhardBartsch, 2 Andreas Stipp, 1 and Hans Joachim Schöpe 11 Johannes Gutenberg Universität, Institut für Physik, 55128, Mainz, Germany2 Albert-Ludwigs-Universität, Freiburg, GermanyUsing a combination of Bragg- and small angle scattering as well as microscopy we study thesolidification of hard sphere - polymer mixtures in real and reciprocal space. Our particles consistof cross-linked Polystyrene spheres swollen in the good solvent 2-Ethylnaphthalene to yieldhard sphere like interactions of buoyancy and refractive index matched particles. To introduce adepletion attraction we either use residual oligomeric chains from synthesis or add small syntheticPolystyrene-polymers. For systems with one colloidal component prepared at fluid-crystalcoexistence we observe drastically altered crystallization kinetics following a t 1/3 growth law.This is traced back to the constraint that the polymers have to leave the forming crystals diffusivelyin order to allow for their larger density. As a result the polymer concentration takes the role of aconserved order parameter [1]. After extended coarsening a pronounced small angle signal occurswhich is due to the formation of a foam-like network of fluid grain boundaries around facettedcrystals, which drains into the Plateau-boarders at the intersection of facets [2]. Adding polymerto a eutectic mixture, we have been able to avoid vitrification at large volume fractions. Instead,we find the precipitation of A and of B crystals for practically all compositions [3]. This for thefirst time demonstrates the existence of the theoretically expected eutectic regime. In additionwe also observe intra-species fractionation with strongly slowed crystallization kinetics whichstrongly supports recent theoretical work of Fasolo and Sollich [4].[1] A. Stipp, T. Palberg, E. Bartsch, Phys. Rev. Lett. 102, 038302 (2009).[2] A. Stipp, T. Palberg, E. Bartsch, R. Biehl, Phys. Rev. E, 81, 051401 (1-10) (2010).[3] A. Kozina, PhD-Thesis, Freiburg, 2010 and Phys. Rev. Lett. submitted (2011).[4] M. Fasolo and P. Sollich, J. Chem. Phys. 122, 07904 (2005).163