The influence of middle B-block polydispersity on the molecular configurations and lamellar structure characteristics of lamella-forming ABA triblock copolymers

Abstract

A recent experimental study (Widin J. M., Schmitt A. K., Schmitt A. L., Im K. and Mahanthappa M. K., J. Am. Chem. Soc., 134 (2012) 3834) showed that polydispersity of the middle B-block has large effects on the phase behavior of ABA triblock copolymers. It is well known that the intriguing properties of ordered structures are associated with the molecular configurations and their distribution at microscale. By using a comprehensive dissipative particle dynamics (DPD) simulation method, we study the effect of middle B-block polydispersity of lamella-forming ABA triblock copolymers on the molecular configurations and the characteristics of lamellar structures. The results show that molecules with short B-blocks in a polydisperse system mainly adopt a looped configuration and preferably locate at the A/B interfaces. On the contrary, the long blocks can adopt either looped or bridged configurations with an equal probability. The bridging fraction of triblock copolymers will decrease with the increase of middle B-block polydispersity, which is due to the fact that there will be more short triblock copolymers adopting looped configurations. Such triblock copolymers with short B-blocks accumulating at the interface region can act as compatibilizers and reduce the interfacial free energy. On the other hand, the domain spacing is mainly determined by the long blocks filling in the domain center. With an increase in middle B-block polydispersity, the domain spacing will expand due to the molecular stretching of the long blocks in the domain center as well as to the reduction in interfacial free energy.