Monte Carlo Study Of The Self-assembly Behavior Of ABCA Tetrablock Copolymers In Selective Solvents

The phase behavior of the ABCA tetrablock copolymers in A-selective solvents isinvestigatedusing Monte Carlo simulation.The main focusis the effects of thesolvophobic 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 diagramsof these three tetrablock copolymers as a function of ε_CS and the solvophobic interaction difference between blocks B and C(which is measuredby 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-structuresof the solvophobic parts of the micelles.For A₂B₇C₅A₂ and A₂B₈C₄A₂ tetrablock copolymers,severalnovel 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 partsisthe 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.