Non-Centrosymmetric Lamellar Structures in the Associating Blends of Tri- and Diblock Copolymers

Abstract

We consider lamellar morphologies in the mixtures of AC diblock and ABC triblock copolymers and show that a proper functionalization of the end blocks of the triblock and diblock copolymer chains by donor and acceptor functional groups, respectively, could result in occurrence of the thermodynamically stable noncentrosymmetric lamellar structures in such mixtures. Depending on the chemical nature of the donor-acceptor bond (i.e., the values of the effective entropy Sbond and energy E per one bond), the typical phase diagrams could contain the upper and lower triple points where the pure diblock, pure triblock and noncentrosymmetric lamellae of a finite composition coexist. With increase of the association strength the triple points merge and the noncentrosymmetric lamellae become thermodynamically favorable at all temperatures. The boundary on the (Sbond ,E)-plane, which separates the regions corresponding to different types of the phase behavior, is found. The influence of the architecture of the system and the chemical nature of the donor-acceptor bond on the stability of the noncentrosymmetric lamellae is analyzed and typical phase diagrams are presented.