Dissipative morphological characteristics of photo-responsive block copolymers driven by time-oscillatory irradiations: An in silico study

Dissipative or dynamic self-assembly has become one of the most important topics in the past twenty years. Under continuous energy input, the building blocks may form various dissipative structures in steady states, which will be destroyed when the energy input is stopped. Among the common forms of energy input, light is widely used for its high efficiency and adjustability. However, there is lack of study on the dissipative selfassembly of photo-responsive block copolymers under time-dependent light irradiations (especially in timeoscillatory light irradiations) as well as its design strategies. We performed non-equilibrium dissipative particle dynamics simulations of azobenzene-contained semiflexible block copolymers in melt and investigated important controlling factors that influence dissipative structures, including the volume ratio of blocks, the interaction between blocks, the oscillation period and the volume fraction of photo-responsive polymers in the system. We found that, when the oscillation period is much smaller than the diffusional timescale of block copolymer, dissipative steady structures will be formed. With the increase of oscillation period, oscillatory dissipative structures with periodic structural variation were formed based on dissipative steady structures. As oscillation period increased further, there would be no regular structure. Furthermore, the dissipative steady structures could be finely tuned by adjusting the volume fraction of photo-responsive chains in block copolymer melt. Our study provides a guidance for the design of azobenzene-contained block copolymers that can form dissipative structures in time-oscillatory irradiations and helps to predict the self-assembled morphologies.

Automated summary

This study investigates the dissipative self-assembly of azobenzene-contained block copolymers under time-dependent light irradiations through non-equilibrium dissipative particle dynamics simulations. It demonstrates that dissipative steady structures can be formed when the oscillation period is much smaller than the diffusional timescale of the block copolymer, and as the oscillation period increases, periodic dissipative structures with structural variation are formed. Additionally, the dissipative steady structures can be finely tuned by adjusting the volume fraction of photo-responsive chains in the block copolymer melt.