  The dynamic behavior of a hard-sphere colloidal suspension was studied by
X-ray Photon Correlation Spectroscopy and Small Angle X-ray Scattering over a
wide range of particle volume fractions. The short-time mobility of the
particles was found to be smaller than that of free particles even at
relatively low concentrations, showing the importance of indirect hydrodynamic
interactions. Hydrodynamic functions were derived from the data and for
moderate particle volume fractions (> 0.40) there is a good agreement with
earlier many-body theory calculations by Beenakker and Mazur [C.W.J. Beenakker
and P. Mazur, Physica A 120, 349 (1984)]. Important discrepancies appear at
higher concentrations, above ~0.40, where the hydrodynamic effects are
overestimated by the Beenakker-Mazur theory, but predicted accurately by an
accelerated Stokesian dynamics algorithm developed by Banchio and Brady [A.J.
Banchio and J. F. Brady, J. Chem. Phys. 118, 10323 (2003)]. For the relaxation
rates, good agreement was also found between the experimental data and a
scaling form predicted by Mode Coupling Theory. In the high concentration
range, with the fluid suspensions approaching the glass transition, the
long-time diffusion coefficient was compared with the short-time collective
diffusion coefficient to verify a scaling relation previously proposed by Segre
and Pusey [P.N. Segre and P.N. Pusey, Phys. Rev. Lett. 77, 771 (1996)]. We
discuss our results in view of previous experimental attempts to validate this
scaling law [L. Lurio et al., Phys. Rev. Lett. 84, 785 (2000)]
