Optical Experiments on a Crystallizing Hard Sphere - Polymer Mixture at Coexistence - Condensed Matter > Soft Condensed MatterReportar como inadecuado




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Abstract: We report on the crystallization kinetics in an entropically attractivecolloidal system using a combination of time resolved scattering methods andmicroscopy. Hard sphere particles are polystyrene microgels swollen in a goodsolvent radius a=380nm, starting volume fraction 0.534 with the short rangedattractions induced by the presence of short polymer chains radius of gyrationrg = 3nm, starting volume fraction 0.0224. After crystallization, stackingfaulted face centred cubic crystals coexist with about 5% of melt remaining inthe grain boundaries. From the Bragg scattering signal we infer the amount ofcrystalline material, the average crystallite size and the number density ofcrystals as a function of time. This allows to discriminate an early stage ofconversion, followed by an extended coarsening stage. The small anglescattering SALS appears only long after completed conversion and exhibitsFurukawa scaling for all times. Additional microscopic experiments reveal thatthe grain boundaries have a reduced Bragg scattering power but possess anincreased refractive index. Fits of the Furukawa function indicate that thedimensionality of the scatterers decreases from 2.25 at short times to 1.65 atlate times and the characteristic length scale is slightly larger than theaverage crystallite size. Together this suggests the SALS signal is duescattering from a foam like grain boundary network as a whole.



Autor: Andreas Stipp, Hans-Joachim Schoepe, Thomas Palberg, Thomas Eckert, Eckhard Bartsch, Ralf Biehl

Fuente: https://arxiv.org/







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