Structure and Dynamics of Block Copolymer Micelles in the Presence of Cosolvents

Amphiphilic diblock copolymers, which form micelle structures in selective solvents, offer a great advantage of tunability in physical characteristics as compared to low molecular weight surfactants. Block copolymer micelles in aqueous solvents are a subject of great interest in drug delivery applications for their high loading capacity and targeted drug delivery. We aim to understand the kinetic and thermodynamic processes which underlie the self-assembly of diblock copolymer micelle systems. The present work focuses on diblock copolymers containing blocks of poly(ethylene oxide) (a hydrophilic polymer) and polycaprolactone (a hydrophobic polymer), which spontaneously self-assemble into spherical micelles in water. Addition of a common good solvent (co-solvent) for both of the constituting blocks, such as tetrahydrofuran (THF), reduces the interfacial tension at the core-corona interface. We are currently investigating the effect of this phenomenon on the micelle structural properties and their dynamics, using the neutron scattering experiments. Structural parameters of interest include hydrodynamic radius, core radius, corona thickness, aggregation number, and the degree of swelling of the micelle core with the co-solvent. In addition, dynamic property of interest is the characteristic time scale of single chain exchange (unimers) between the micelles. Both structural and dynamic parameters are examined as the interfacial tension at the core-corona interface is varied through changing the co-solvent concentration.