  In this work we study the aging behavior of aqueous suspension of Laponite
having 2.8 weight % concentration using rheological tools. At various salt
concentration all the samples demonstrate orientational order when observed
using crossed polarizers. In rheological experiments we observe inherent
irreversibility in the aging dynamics which forces the system not to rejuvenate
to the same state in the shear melting experiment carried out at a later date
since preparation. The extensive rheological experiments carried out as a
function of time elapsed since preparation demonstrate the self similar trend
in the aging behavior irrespective of the concentration of salt. We observe
that the exploration of the low energy states as a function of aging time is
only kinetically affected by the presence of salt. We estimate that the energy
barrier to attain the low energy states decreases linearly with increase in the
concentration of salt. The observed superposition of all the elapsed time and
the salt concentration dependent data suggests that the aging that occurs in
low salt concentration systems over a very long period is qualitatively similar
to the aging behavior observed in systems with high salt concentration over a
shorter period.
