  We investigate the spontaneous evolution of various self-assembled phase
states from a homogeneous aqueous dispersion of high-aspect ratio
Montmorillonite (Na Cloisite) nanoclay platelets grounded on the observations
made over a period of 3.5 years. We have established the tw-c phase diagram for
this system for the first time in salt-free suspensions under normal pH
conditions using rheology experiments and have detected that these suspensions
do undergo nontrivial phase evolution and aging dynamics. Distinctive phase
separation, equilibrium fluid and equilibrium gels in the tw-c phase space are
discovered. Cole-Cole plots derived from rheology measurements suggested the
presence of inter connected network-like structures for c > cg, cg being the
gelation concentration. All dispersions formed stable sols during the initial
time, and with aging network-like structures were found to form via two routes:
one for c < cg, by phase separation and another for c > cg, through equilibrium
gelation. This has invoked and called for a revisit of the phase diagram of
aging MMT dispersions.
