Monte Carlo study of the micelles constructed by ABCA tetrablock copolymers and their formation in A-selective solvents

Abstract

The phase behavior of the ABCA tetrablock copolymers in A-selective solvents is investigated using Lattice Monte Carlo simulation. The main focus is the effects of the solvophobic interactions of blocks B and C (ε_BS and ε_CS) on the micelle morphologies. Three kinds of ABCA tetrablock copolymers, i.e., A₂B₆C₆A₂, A₂B₇C₅A₂ and A₂B₈C₄A₂ tetrablock copolymers, are considered. Phase diagrams of these three tetrablock copolymers as a function of ε_CS and the solvophobic interaction difference between blocks B and C (which is measured by r = ε_BS/ε_CS) are given and discussed. It is found that r and ε_CS can both affect the specific surface area of micelles and lead to the morphological changes of ABCA tetrablock copolymer micelles. In addition, r can change the solvophobic chain conformation and hence affect the micro-structures of the solvophobic parts of the micelles. For A₂B₇C₅A₂ and A₂B₈C₄A₂ tetrablock copolymers, several novel micelle morphologies, such as the bended Janus ribbon and lamella, short Janus tube, and bowl-shaped semivesicle, are obtained. Interestingly, it is found that in the phase diagrams of A₂B₇C₅A₂ and A₂B₈C₄A₂ tetrablock copolymers, the micelle type with Janus-like solvophobic parts is the majority micelle type, which mainly results from the solvophobic interaction balance between blocks B and C. Moreover, the formation pathways for these novel Janus-type micelles are given and discussed.