Morphological control of oppositely charged block copolymer Micelle in aqueous solution

Abstract

It is well known that amphiphilic diblock copolymers, a specific kind of block copolymers composed of hydrophobic and hydrophilic segments, self-assemble into aggregates of various morphologies in selective solvents. Here, we investigate these diverse morphologies as a function of pH, solvent quality (wt%), and molecular weight ratio of PS-b-PAA and PS-b-P4VP block copolymers. First part of this research focuses on the morphological study of complexation of two oppositely charged PS-b-PAA block copolymer micelle (BCM) and PS-b-P4VP BCM. Second part of the research focuses on hierarchical microphase separation induced by pH-sensitive segregation of block segments. By adjusting the pH of aqueous solution, we were able to selectively segregate coronas at extreme pH values: pH 9 or higher, and pH 3 or lower. At a pH value of 9 and higher, only PAA block are segregated as coronas and P4VP blocks constitute the internal structure within the cores of the block copolymer micelles (BCM). This segregation is based on the difference in repulsive interactions within PAA or P4VP corona under different pH conditions. These experimental observations are of fundamental significance both for understanding the phase behavior and morphology of block copolymers and also for various potential applications, for example dielectric resonators, spherical photonic crystals, and the internal isolated regions can also be used as a new type of ideal compartments in controlled drug delivery systems.