Recent advances in the study of soft materials have led in the last decades to a deeper knowledge of equilibrium and non equilibrium states and to the discovery of new phases besides the ones commonly experienced in atomic or molecular systems. Colloidal suspensions are characterized by a variety of microscopic interactions which generate complex and exotic phase diagrams encompassing fluid, gel and glassy states and offer the possibility to study new phase and/or state transitions. Among these glass-glass transitions are quite rare to be found, especially at ambient conditions. Here we report experimental and numerical evidence of a spontaneous glass-glass transition taking place during aging of a colloidal clay. In this work we investigate the aging behaviour of a colloidal clay through a combination of dilution experiments, X-Ray Photon Correlation Spectroscopy (XPCS) [1], Small Angle X-ray Scattering (SAXS) rheological measurements and Monte Carlo (MC) simulations. Two different glassy states are distinguished with evolving waiting time: a first one, occurring at the arrest transition (after a waiting of the order of hours), is dominated by long range screened Coulombic repulsion (Wigner glass) and a second one, previously unreported and stabilized by orientational attractions between clay platelets (Disconnected House of Cards (DHOC) glass) is found at much longer waiting times (of the order of days). These findings may have relevance for applications where a fine control of the local order and/or long term stability of amorphous materials are required [2].
[1] R. Angelini et al. 9, 10955, Soft Matter (2013) accepted (2014)
[2] R. Angelini et al. Nature Communications
