Development of ultra-small-angle X-ray scattering-X-ray photon correlation spectroscopy

This paper describes the development of ultra-small-angle X-ray scattering-X-ray photon correlation spectroscopy (USAXS-XPCS). This technique takes advantage of Bonse-Hart crystal optics and is capable of probing the long-time-scale equilibrium and non-equilibrium dynamics of optically opaque materials with prominent features in a scattering vector range between those of dynamic light scattering and conventional XPCS. Instrumental parameters for optimal coherent-scattering operation are described. Two examples are offered to illustrate the applicability and capability of USAXS-XPCS. The first example concerns the equilibrium dynamics of colloidal dispersions of polystyrene microspheres in glycerol at 10, 15 and 20% volume concentrations. The temporal intensity autocorrelation analysis shows that the relaxation time of the microspheres decays monotonically as the scattering vector increases. The second example concerns the non-equilibrium dynamics of a polymer nanocomposite, for which it is demonstrated that USAXS-XPCS can reveal incipient dynamical changes not observable by other techniques.