Effect of Chain Architecture on the Compatibility of Block Copolymer/Nanoparticle Blends

Abstract

The effect of block copolymer chain connectivity on the structure formation in binary blends comprising block copolymer hosts and enthalpically neutralized particle fillers is investigated for linear diblock (AB) and triblock (ABA and BAB) as well as four-arm star copolymer architectures (AB3 and A3B). For particles with approximately constant effective size (defined here as the ratio of filler particle diameter to host polymer radius of gyration), miscibility was observed only within diblock copolymers and within the domains formed by the end blocks of triblock copolymers. The limitation of particle miscibility within the triblock mid-domain is interpreted as a consequence of the entropy loss associated with particle deposition due to the stretched configuration of bridged midblock chains. Particle aggregation was observed in both star copolymer samples irrespective of the architecture of the particle-loaded polymer domain. In the case of particle loading of the branched copolymer domain, this is rationalized as a consequence of the increased effective particle size, whereas the incompatibility of particle fillers in the linear block domain of miktoarm copolymer hosts is interpreted as a result of the coupling of dimensional changes within the microstructure along with the reduced axial compressibility of the particle-free branched domain. The sensitive dependence of the particle compatibility on the chain architecture of the polymer host illustrates a yet unexplored parameter space that will need to be taken into account if particle blends are to be designed with branched or multiblock host copolymer architectures.