Glassy dynamics and aging in a dense ferrofluid

X-ray Photon Correlation Spectroscopy is used here to probe for the first time a glass-forming dispersion of repulsive particles spherical and 10 nm sized. The highly concentrated colloidal system is based on the magnetic and charge-stabilized nanoparticles of a ferrofluid. Their out-of-equilibrium translational dynamics capture on nanoscale generic features usually observed on microscale: namely i) stretched exponential a relaxation with an exponent around 1.5 and ii) age-dependent characteristic time tau evolving from exponential at young ages to a slower behavior at large ages. tau is here scaling as Q(-1) in the whole experimental Q-range, below, on and above the scale of the interparticle distance, the driving force for aging in this glass-forming nanosystem being associated to larger scale rearrangements.