  In order to find a measure of the dynamical features of phase separation
kinetics during spinodal decomposition of a liquid binary mixture (like water
and cyclohexane , water and 2,6 lutidiene or methanol and cyclohexane), we
study both the initial fast exponential-like growth (the Cahn-Hilliard regime)
and the subsequent cross-over to a much slower, non-exponential long time
growth (the so-called scaling regime), by atomistic molecular dynamics (MD)
simulation of a structure breaking binary liquid mixture. In particular, we
combine our MD simulations with a coarse grained multi scale modelling (CGMSM)
capable of capturing both length and time scales of phase separation kinetics
within simulation box. The system is quenched from a higher temperature to two
lower temperatures well below the coexistence temperature of the phase diagram.
We observe a multiscale phase separation dynamics. Initially the growth is
exponential up to a regime of 80-100ps having strong dependence over quench
depth. Subsequently a cross-over regime appears where the dynamics slows down
considerably due to coarsening through a power law phase. For deeper quench
power law growth dominates over the initial exponential and the cross-over
becomes transient. We find that for the present parameter values for the binary
mixture, the initial rapid growth of structure formation is practically over
within 200 ps which is followed by slow structural coarsening. When scaled by
the respective viscosities, this time translates to 50-200 ns for
water-lutidine binary mixture. The last part of dynamics may extend into ms.
The dynamics of phase separation is slowest in regions that have equitable
distribution of the two species, and one can observe the signatures of "up-hill
diffusion" that is a trade mark of spinodal decomposition.
