Regensburg 2019 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 25: Poster Session II

CPP 25.7: Poster

Dienstag, 2. April 2019, 14:00–16:00, Poster B1

Competing nucleation and fractionation in hard sphere crystals — •Nicole Schaertl1, Jennifer Wenzl1, Thomas Palberg1, and Eckhard Bartsch21Institute of Physics, Johannes Gutenberg University, Mainz, Germany — 2Institute of Physical Chemistry, Albert Ludwigs University, Freiburg, Germany

Fluid to crystal first order phase transition of monodisperse hard spheres (HS) upon increasing volume fraction was predicted in the 1950s and later confirmed experimentally on sterically stabilized HS approximants [1]. In particle synthesis, size polydispersity is unavoidable. According to theory, a polydisperse fluid should yield coexisting solid phases upon compression [2]. Despite the general anticipation towards fractionation in HS systems, no direct observation has been reported so far. We decided to focus on PS microgel particles with 6% polydispersity in a good solvent. Sufficiently steep steric repulsion for HS-like behavior is obtained at high degree of crosslinking. Recent studies have shown that this colloidal system is less prone to jamming effects than other common HS approximants [3]. This makes this systems particularly interesting for crystallization studies. Time resolved static light scattering revealed several series of well indexable Bragg reflexes shortly after shear melting and re-solidification. This demonstrates the existence of crystals with same fcc structure but different lattice constants. During ripening stage the number of identifiable fractions slowly reduces from half a dozen to three. [1] Pusey, van Megen, Nature 320, 340 (1986) [2] Fasolo, Sollich, Phys. Rev. Lett. 91, 068301 (2003) [3] Schaertl et al., Soft Matter, 14, 5130 (2018)

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