title: Structure and dynamics studies of concentrated micrometer-sized colloidal suspensions.
abstract: We present an experimental study of the structural and dynamical properties of concentrated suspensions of different sized polystyrene microspheres dispersed in glycerol for volume fraction concentrations between 10% and 20%. The static structure, probed with ultrasmall-angle X-ray scattering, shows a behavior very similar to that of hard spheres. The equilibrium dynamics is probed with ultrasmall-angle X-ray scattering-X-ray photon correlation spectroscopy, a new technique that overcomes the limits of visible light-scattering techniques imposed by multiple scattering and is suitable for studies of optically opaque materials containing micrometer-sized structures. We found that the intensity autocorrelation functions are better described by a stretched exponential function and microspheres in a concentrated suspension move collectively. We also found that the inverse of the effective diffusion coefficients displays a peak with respect to the scattering vector that resembles the peaks in the static structure factors, which indicates that a long-lived, low free-energy state exists. The relaxation time is approximately inversely related to scattering vector, a behavior consistent with models that describe the dynamics in terms of random, local structural arrangements in disordered media.
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States. fan.zhang@nist.gov
authors.forename: Fan
authors.initials: F
authors.lastname: Zhang
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Allen
authors.forename: Lyle E
authors.initials: LE
authors.lastname: Levine
authors.forename: Jan
authors.initials: J
authors.lastname: Ilavsky
authors.forename: Gabrielle G
authors.initials: GG
authors.lastname: Long
mesh_terms: D003102:Colloids / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D010316:Particle Size; D013499:Surface Properties; D013535:Suspensions / Q000138:chemical synthesis / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D003102:Colloids; D013535:Suspensions