Hierarchical Assembly of Complex Block Copolymer Nanoparticles into Multicompartment Superstructures through Tunable Interparticle Associations
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A challenging aim in both materials physics and chemistry is the construction of complex and functional superstructures from designed nanoscale building units. Block copolymer nanoparticles with morphological variety and compositional complexity have been made with solution-based assembly. However, routine ability to build hierarchical superstructures by inter-nanoparticle association is not yet possible. A hierarchical assembly strategy of organizing pre-formed spherical block copolymer nanoparticles into superstructures, including linear, circular, and close-packed arrays, via tunable interparticle interactions is presented. Solution-state mixtures are made of two amphiphilic diblock copolymers, poly(acrylic acid)-block-poly(methyl methacrylate) (PAA-b-PMMA) and poly(acrylic acid)-block-polybutadiene (PAA-b-PB) with additional crown ether functionalities grafted onto 40 mol% of the AA repeat units on the PAA-b-PMMA diblock copolymer. Through kinetic control of the solution assembly process in aqueous/N,N-dimethylformamide (DMF) mixtures (4:1 water:DMF), spherical nanoparticles with compositional complexity confined in both the core and shell are obtained. Benefiting from host-guest chemistry, interparticle association is triggered and tuned by the addition of di-functional organoamines due to amine-crown ether complexation. The resultant multiparticle superstructures contain well-defined multicompartments within individual, constituent nanoparticles due to the local separation of unlike PB and PMMA hydrophobic blocks within the cores of the individual particles. Through competitive complexation with potassium ions, the superstructures are disassembled into individual multicomparment nanoparticles. Isolated, complex micelle-like nanoparticles assemble through a solvent mixing process from a binary diblock copolymer mixture with a crown ether modification on only one diblock copolymer. Particle-particle association is triggered by the addition of diamines to the solution resulting in uniform particle-chain and particle-ring superstructures. Further dissociation of the superstructures can be triggered by the addition of potassium ions into the solution. Importantly, manipulated by the shell interactions between the neighboring particles, varied phase segregation occurs in the micelle core giving rise to novel multicompartment nanoparticles. Copyright 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
