Phase behaviour of Polydisperse Diblock Copolymers

Recent experimental and theoretical studies have shown that many ordered structures, ranging in complexity from simple lamellae to complex Frank-Kasper (FK) phases, can be formed from diblock copolymers. While most theoretical studies have been based on monodisperse systems, almost all the polymeric samples used in experiments are polydisperse. It is therefore desirable to carry out theoretical studies on the phase behaviour of polydisperse block copolymer systems. In our study, the molecular weight distribution of AB diblock copolymers is modeled as a blend with four components. The effects of the shape of the molecular weight distribution (MWD) are studied by using the self-consistent field theory. It is found that the width and skewness of the MWD, as well as the conformational asymmetry, have significant effects on the formation of the FK phases. The theoretical results shed light on the formation mechanisms of the FK phases and provide insight to regulating block copolymer phase behaviours via designed molecular weight distributions.