Self-assembly of grafted nanoparticles in the lamellar mesophase of a symmetric triblock copolymer

Abstract

The self-assembly behavior of brush-grafted nanoparticles in the ordered mesophase of a symmetric triblock copolymer is studied using the self-consistent field theory. The emphasis is on the templated localization of nanoparticles in a two-dimensional lamellar microstructure formed by an ABA triblock copolymer. While particles grafted with either A-type or B-type polymeric chains preferentially localize in the respective micro-domain, the spatial distribution of particles within the selective domain is of great interest in controlling the properties of the nano-ordered morphologies. As the mid-block of an ABA triblock copolymer is entropically constrained, the localization behavior of B-grafted nanoparticles is found to be qualitatively different from that of A-grafted particles. The absence of free ends and the bridge conformation of the mid-block tend to reduce the spatial segregation of B-grafted particles at the center of the B-domain, a behavior in contrast to an AB diblock copolymer. Under similar conditions, while A-grafted particles self-assemble at the center of the A-domain, the B-grafted particles with a non-selective core segregate predominantly at the interface of A and B domains, especially when the particle size is large or grafting is weak. Upon increasing the grafting density, the morphology transitions from interface to center localization. The spatial localization of particles, governed by the interplay of enthalpic and entropic contributions to the free energy, is found to be strongly influenced by particle size, selectivity, volume fraction, and number and size of grafted chains. Controlling the self-assembly behavior of particles by tuning these parameters will be immensely helpful in designing advanced nanostructured materials with desired physical properties.