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Abstract: During directional solidification of the solvent in a colloidal suspension,the colloidal particles segregate from the growing solid, forminghigh-particle-density regions with structure on a hierarchy of length scalesranging from that of the particle-scale packing to the large-scale spacingbetween these regions. Previous work has concentrated mostly on the medium- tolarge-length scale structure, as it is the most accessible and thought to bemore technologically relevant. However, the packing of the colloids at theparticle-scale is an important component not only in theoretical descriptionsof the segregation process, but also to the utility of freeze-cast materialsfor new applications. Here we present the results of experiments in which weinvestigated this structure across a wide range of length scales using acombination of small angle x-ray scattering and direct optical imaging. Asexpected, during freezing the particles were concentrated into regions betweenice dendrites forming a microscopic pattern of high- and low-particle-densityregions. X-ray scattering indicates that the particles in the high densityregions were so closely packed as to be touching. However, the arrangement ofthe particles does not conform to that predicted by standard inter-particlepair potentials, suggesting that the particle packing induced by freezingdiffers from that formed during equilibrium densification processes.



Author: Melissa Spannuth, S. G. J. Mochrie, S. S. L. Peppin, J. S. Wettlaufer

Source: https://arxiv.org/



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