Amphiphilic Inorganic Nanoparticles with Mixed Polymer Brush Layers of Variable Composition: Bridging the Paradigms of Block Copolymer and Nanoparticle Self-Assembly

Abstract

The application of molecular self-assembly principles to nanoscopic building blocks can inform new pathways to hierarchical nanomaterials. For instance, amphiphilic brush nanoparticles (ABNPs) are inorganic nanoparticles functionalized with mixed polymer brushes of hydrophobic and hydrophilic chains that possess several structural and chemical features similar to those of amphiphilic block copolymers (ABCs), including spatial segregation of covalently connected hydrophilic and hydrophobic regions, anisotropic interactions, and conformational flexibility. However, the phase behavior of ABNPs with respect to hydrophobic fraction, concentration, and salt content has not been established to date, precluding direct comparison with ABC self-assembly. In this study, we produce and characterize a series of ABNPs with similar cadmium sulfide core sizes and brush densities but with different polystyrene/poly(methacrylic acid) brush compositions using a diblock copolymer mixed micelle approach. Self-assembly of the resulting ABNPs in THF/water mixtures yields hybrid spheres, cylinders, and vesicles with morphological transitions following trends with respect to hydrophobic fraction, initial concentration, and salt content similar to those previously established for ABCs. The resulting ABNP phase behavior demonstrates that microphase separation principles established in the 1990s for the solution self-assembly of macromolecular ABCs can provide vital experimental guidelines for the controlled self-organization of nanoscopic amphiphiles.