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- Colloidal grain boundaries decorated by nanoparticles: a multi-scale study by confocal microscopy, very small angle light scattering, and contrast-variation SANS

Auteur(s): Tamborini E., Ghofraniha N., Oberdisse J., Cipelletti L., Ramos L.

Conference: ECIS 2011 (Berlin, DE, 2011-09-04)


Résumé:

The structure and rheology of polycrystals is relevant in particular for metals, where post mortem studies are usually performed. In colloidal crystalline systems, the accessible size range makes in-situ investigations possible, under flow and at rest. In this project, termed ‘colloidal metallurgy’, a polycrystalline material is formed spontaneously at high concentrations (34%wt) of spherical Pluronics micelles (F108) in water. The crystalline grains have a local FCC structure (lattice constant 30 nm), and are separated from neighbouring grains of different orientation by grain boundaries (GB), cf. Fig 1, where fluorescent nanoparticles of size comparable to the lattice parameter have been added to visualize the GBs. We have determined the size distribution of grains for different crystallization speeds and nanoparticle contents (typically below 1%). In particular, a universal relationship between grains size and thermal history, and between grain size and amount of nanoparticles has been found, in agreement with theoretical considerations based on classical nucleation theory and constitutional under-cooling. The microscopic structure of silica-containing polycrystals has been studied by contrast-variation small angle neutron scattering, highlighting either the particles or the polymer micelles. The local micellar structure is found to be unaffected by the nanoparticles, which are shown to segregate predominantly in dense zones, presumably GBs. Very small-angle light scattering is currently used to characterize the mesostructure, and the influence of deformation and flow is investigated in a confocal rheo set-up. An alternative view of our findings is that we present here a general approach to confine nanoparticles in colloidal materials in a controlled fashion, independent of the details of the surface chemistry.