Photo-induced bond breaking during phase separation kinetics of block copolymer melts: a dissipative particle dynamics study

AK Singh and A Chauhan and S Puri and A Singh, SOFT MATTER, 17, 1802-1813 (2021).

DOI: 10.1039/d0sm01664k

Using a dissipative particle dynamics (DPD) simulation method, we study the phase separation dynamics in block copolymer (BCP) melts 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 allow the system to undergo alternate light "on" and "off" cycles. An on-cycle breaks the stimuli-sensitive bonds connecting both the blocks A and B in the BCP melt, and during the off-cycle, the broken bonds recombine. 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 bond breaking. Here, we report the role of alternate cycles on domain morphology by varying the bond-breaking probability for both set 1 and set 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) similar to t(phi) at late times, where phi is the dynamic growth exponent. After a short-lived diffusive growth (phi similar to 1/3) at early times, phi illustrates a crossover from the viscous hydrodynamic (phi similar to 1) to the inertial hydrodynamic (phi similar to 2/3) regimes at late times.

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