Efficacy of Different Block Copolymers in Facilitating Microemulsion Phases in Polymer Blend Systems

Polymeric microemulsions are formed in a narrow range of phase diagram when a blend of immiscible homopolymers is compatibilized by copolymers. In this study, we consider the ternary blend system of A and B homopolymers mixed with block copolymers containing A and B segments and probe the efficacy of different copolymer configurations in promoting the formation of microemulsion phases. Specifically, we consider (a) monodisperse diblock copolymers (D), (b) diblock copolymers with bidisperse molecular weights (MW) (BDL), (c) block copolymers having MW polydispersity in one of the blocks (PD), (d) diblock copolymers having monodisperse MW but bidispersity in average composition (BDC), and (e) gradient copolymers exhibiting a linear variation in the average composition (G). Using single chain in mean field simulations effected in two dimensions, we probe the onset of formation and the width of the bicontinuous microemulsion channel in the ternary phase diagram of homopolymer blended with compatibilizer. We observed that diblock copolymers having bidisperse composition are most efficient (i.e., microemulsion phases occupy the largest area of phase diagram) in forming microemulsions. On the other hand, monodisperse diblock copolymers and diblock copolymers having bidisperse MW distribution form microemulsions with the least amount of compatibilizers. We rationalize our results by explicitly quantifying the interfacial activity and the influence of fluctuation effects in the respective copolymer systems