Phase behavior of binary mixtures of block copolymers and a non-solvent in miniemulsion droplets as single and double nanoconfinement

Abstract

Nanoparticles consisting of different molecular weight poly(styrene-block-methyl methacrylate) (P(S-b-MMA)) copolymers and nanocapsules consisting of the same copolymers, but additionally with hexadecane as liquid core material were prepared by the miniemulsion process. The dependence of the morphology of block copolymer assemblies on the nanoconfinement was investigated. We introduced two nanoconfinement parameters, that are the nanoparticle diameter D and the shell thickness d; D was controlled by varying the concentration of surfactant in the miniemulsion, while d was controlled by the ratio hexadecane/copolymer. As the diameter D of the high molecular weight (M_w ∼ 203,700 g mol⁻¹) P(S-b-MMA) nanoparticles increased, first Janus-particles (at D < 60 nm), then core-shell structures (60 nm < D < 90 nm), onion-like nanoparticles (90 nm < D < 1800 nm) and finally terrace-like morphologies (D > 1800 nm) were obtained. Nanocapsules with 0 < d < D also showed an onion-like structure. In both cases the outmost layer was PMMA as identified by XPS and the lamellar thickness was in agreement with theoretical considerations. Nanoparticles and nanocapsules prepared with a low-molecular weight (M_w ∼ 19,500 g mol⁻¹) P(S-b-MMA) displayed patchy structures. This is the first time that the morphology of block copolymers was studied under double nanoconfinement in colloids.