Using experiments, theory and simulations, we show that the arrested state observed in a colloidal clay at high concentrations is stabilized by screened Coulomb repulsion (Wigner glass). Dilution experiments allow us to distinguish this disconnected state, which melts upon addition of water, from a low-concentration gel state, which does not melt. Theoretical modeling and simulations at high concentrations reproduce the measured small angle x-ray scattering static structure factors and confirm the long-range electrostatic nature of the arrested structure. These findings are attributed to the different time scales controlling the competing attractive and repulsive interactions.

An unexpected dichotomic long time aging behaviour is observed in a glassy colloidal clay suspension investigated by X-ray photon correlation spectroscopy and dynamic light scattering. In the long time aging regime the intensity autocorrelations are non-exponential, following the Kohlrausch–Williams–Watts functional form with an exponent β_Q. We show that for spontaneously aged samples a stretched behaviour (β_Q < 1) is always found. Surprisingly a compressed exponent (β_Q > 1) appears only when the system is rejuvenated by application of a shear field. In both cases the relaxation times scale as Q⁻¹. These observations shed light on the origin of compressed exponential behaviour and help in classifying previous results in the literature on anomalous dynamics.

The aging of a charged colloidal system has been studied by small-angle x-ray scattering, in the exchanged momentum range $Q=0.03–5{\mathrm{nm}}^{-1}$, and by dynamic light scattering, at different clay concentrations $(C_w=0.6–2.8\%)$. The static structure factor $S\left(Q\right)$ has been determined as a function of both aging time and concentration. This is the direct experimental evidence of the existence and evolution with aging time of two different arrested states in a single system simply obtained only by changing its volume fraction: an inhomogeneous state is reached at low concentrations, while a homogeneous one is found at high concentrations.

Using inelastic x-ray scattering we studied the collective dynamics of the glassy alloy ${\mathrm{Ni}}_{33}{\mathrm{Zr}}_{67}$ in the first pseudo-Brillouin-zone, an energy-momentum region still unexplored in metallic glasses. We determine key properties such as the momentum transfer dependence of the sound velocity and of the acoustic damping, discussing the results in the general context of recently proposed pictures for acoustic dynamics in glasses. Specifically, we demonstrate the existence in this strong glass of well defined (in the Ioffe-Regel sense) acoustic-like excitations well above the boson peak energy.