Berlin 2005 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 22: Colloids
CPP 22.1: Vortrag
Dienstag, 8. März 2005, 11:15–11:30, TU C243
Mixtures of Colloids and Liquid Crystals — •Doris Vollmer1, Beate Ullrich1, Gerald Hinze2, and Andy Schofield3 — 1MPI für Polymerforschung, Mainz — 2Inst. Physik. Chemie, Univ. Mainz, Mainz — 3School of Physics, The University of Edinburgh, Edinburgh, UK
We studied three-dimensional particle networks that form upon cooling of suspensions of polyacrylmethacrylate colloids (PMMA) in liquid crystal (5CB) through the isotropic-nematic transition. By polarization microscopy we determined the velocity of the particles during the transition. Rheological data suggest that network formation depends only weakly on particle size within the range of 100-800nm. NMR and calorimetry indicate the presence of isotropic material down to 10K below the bulk transition temperature and smearing of the specific heat curve, strongly reminiscent of the effect of alcanes on phase transition kinetics. We suggest that alcane impurities may alter the temperature and time range of phase transition and, due to coexisting isotropic and nematic regions and wetting of the particles with isotropic material, promote rearrangement of the colloids in networks. During subsequent cooling/heating cycle, networks were only partially reversible and exhibited consiberable memory effects even with periods of several hours above transition temperature. Repeated cooling led to compactification and further increase of storage and loss moduli.