  Using dissipative particle dynamics (DPD) simulation method, we study the
phase separation dynamics in block copolymer (BCP) melt in $d=3$, subjected to
external stimuli such as light. An initial homogeneous BCP melt is rapidly
quenched to a temperature $T < T_c$, where $T_c$ is the critical temperature.
We then let the system go through alternate light "on" and "off" cycles. An
on-cycle breaks the stimuli-sensitive bonds connecting both the blocks A and B
in BCP melt, and during the off-cycle, broken bonds reconnect. By simulating
the effect of light, we isolate scenarios where phase separation begins with
the light off (set 1); the cooperative interactions within the system allow it
to undergo microphase separation. When the phase separation starts with the
light on (set 2), the system undergoes macrophase separation due to the bond
breaking. Here, we report the role of alternate cycles on domain morphology by
varying bond-breaking probability for both the sets 1 and 2, respectively. We
observe that the scaling functions depend upon the conditions mentioned above
that change the time scale of the evolving morphologies in various cycles.
However, in all the cases, the average domain size respects the power-law
growth: $R(t)\sim t^{\phi}$ at late times, here $\phi$ is the dynamic growth
exponent. After a short-lived diffusive growth ($\phi \sim 1/3$) at early
times, $\phi$ illustrates a crossover from the viscous hydrodynamic ($\phi \sim
1$) to the inertial hydrodynamic ($\phi \sim 2/3$) regimes at late times.
