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

TL;DR

This study uses dissipative particle dynamics simulations to investigate how light-induced bond breaking influences phase separation and domain morphology in block copolymer melts, revealing power-law growth and dynamic regime crossovers.

Contribution

It introduces a simulation approach to analyze the effects of light-triggered bond breaking on phase separation dynamics in block copolymer melts, highlighting the impact of external stimuli cycles.

Findings

Average domain size follows a power-law growth over time.

Crossover from viscous to inertial hydrodynamic regimes observed.

Bond-breaking cycles significantly alter phase separation morphology.

Abstract

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.