TY - JOUR
T1 - Observation of a shape-dependent density maximum in random packings and glasses of colloidal silica ellipsoids
AU - Sacanna, S.
AU - Rossi, L.
AU - Wouterse, A.
AU - Philipse, A. P.
PY - 2007/9/19
Y1 - 2007/9/19
N2 - We have measured the random packing density of monodisperse colloidal silica ellipsoids with a well-defined shape, gradually deviating from a sphere shape up to prolates with aspect ratios of about 5, to find for a colloidal system the first experimental observation for the density maximum (at an aspect ratio near 1.6) previously found only in computer simulations of granular packings. Confocal microscopy of ellipsoid packings, prepared by rapidly quenching ellipsoid fluids via ultra-centrifugation, demonstrates the absence of orientational order and yields pair correlation functions very much like those for random sphere packings. The density maximum, about 12% above the Bernal random sphere packing density, also manifests itself as a maximum in the hydrodynamic friction that resists the swelling osmotic pressure of the ellipsoid packings. The existence of the density maximum is also predicted to strongly effect the dynamics of colloidal non-sphere glasses: slightly perturbing the sphere shape in a sphere glass will cause it to melt.
AB - We have measured the random packing density of monodisperse colloidal silica ellipsoids with a well-defined shape, gradually deviating from a sphere shape up to prolates with aspect ratios of about 5, to find for a colloidal system the first experimental observation for the density maximum (at an aspect ratio near 1.6) previously found only in computer simulations of granular packings. Confocal microscopy of ellipsoid packings, prepared by rapidly quenching ellipsoid fluids via ultra-centrifugation, demonstrates the absence of orientational order and yields pair correlation functions very much like those for random sphere packings. The density maximum, about 12% above the Bernal random sphere packing density, also manifests itself as a maximum in the hydrodynamic friction that resists the swelling osmotic pressure of the ellipsoid packings. The existence of the density maximum is also predicted to strongly effect the dynamics of colloidal non-sphere glasses: slightly perturbing the sphere shape in a sphere glass will cause it to melt.
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U2 - 10.1088/0953-8984/19/37/376108
DO - 10.1088/0953-8984/19/37/376108
M3 - Article
AN - SCOPUS:47949119522
SN - 0953-8984
VL - 19
JO - Journal of Physics Condensed Matter
JF - Journal of Physics Condensed Matter
IS - 37
M1 - 376108
ER -