Colloidal suspensions of spherical particles presenting hard-sphere like interactions is one of the simplest and most widely studied systems of soft condensed matter. They can be treated as a model for testing fundamental theories, regarding e.g. crystallization [5] or glass transition [6].

Despite the long history of both theoretical and experimental research, the behavior of hard sphere suspensions still lacks complete understanding.

X-ray Photon Correlation Spectroscopy (XPCS) is a coherent scattering technique equivalent to Dynamic Light Scattering (DLS)[3], which is one of the main tools used in the study of colloidal dynamics [1]. Comparing to visible light, the use of X-rays provides access to higher momentum transfer vector values and allows to avoid multiple scattering - a phenomena significantly complicating DLS measurements on concentrated samples. Moreover, the use of a fast, single photon counting area detector (MAXIPIX) available at the ID10 beamline at ESRF gives insight into the evolution of sample dynamics during the measurement time by the means of two-time correlation functions.

XPCS measurements of sterically stabilized colloidal spheres at high volume fractions (Φ > 0.5) below the glass transition show both short- and long-time diffusive behavior for scattering vector values around, but not restricted to the structure factor peak position. A comparison with earlier study [4] shows a dramatic change in the approximate scaling between the short- and long-time relaxation rates [7] over a small range of volume fractions. A combination of XPCS with flow has demonstrated previously to give both dynamic and flow properties of dilute suspensions [2].

Here we discuss the potential and limitations of this method in the study of the interplay between rheological properties and dynamics in complex systems such as colloidal glasses.

References

[1] B. J. Berne and R. Pecora. Dynamic Light Scattering with application to chemistry, biology and physics. Dover Publications, New York, 2000.
[2] A. Fluerasu, P. Kwasniewski, C. Caronna, F. Destremaut, J.-B. Salmon, and A. Madsen. Dynamics and rheology under continuous shear ow studied by x-ray photon correlation spectroscopy. New Journal of Physics, 12(3):035023, 2010.
[3] V. A. Martinez, J. H. J. Thijssen, F. Zontone, W. van Megen, and G. Bryant. Dynamics of hard sphere suspensions using dynamic light scattering and x-ray photon correlation spectroscopy: Dynamics and scaling of the intermediate scattering function. The Journal of Chemical Physics, 134(5):054505, 2011.
[4] D. Orsi, A. Fluerasu, A. Moussaïd, F. Zontone, L. Cristofolini, and A. Madsen. Dynamics in dense hard-sphere colloidal suspensions. Phys. Rev. E, 85:011402, Jan 2012.
[5] P. N. Pusey and W. van Megen. Phase behaviour of concentrated suspensions of nearly hard colloidal spheres. Nature, 320(6060):340{342, Mar. 1986.
[6] P. N. Pusey and W. van Megen. Observation of a glass transition in suspensions of spherical colloidal particles. Phys. Rev. Lett., 59:2083{2086, Nov 1987.
[7] P. N. Segrè and P. N. Pusey. Scaling of the dynamic scattering function of concentrated colloidal suspensions. Phys. Rev. Lett., 77(4):771{774, Jul 1996.