Formation of Interconnected Morphologies of Symmetrical Block Copolymer/Nanorod Comoposites Under Cylindrical Confinement: A Coarse-Grained Molecular Dynamics Study

Our recent experiment and simulation on confined self-assembly of block copolymer (BCP)/nanoparticle (NP) composites in electrospun nanofiber have proven to be a useful guidance for fabrication of the composite materials with ordered nanostructures. Specifically, we have examined how nanoparticle presence can influence the formation of very different asymmetrical BCP morphologies under cylindrical confinement when compared with that of pure asymmetrical BCP, both qualitatively and quantitatively. Using the same coarse-grained molecular dynamics tool, we have further extended our study to self-assembly of nanorods with BCP under cylindrical confinement. Unlike nanoparticles, nanorods can readily be interconnected with each other, and also induce asymmetrical BCP morphologies at much lower loading that nanoparticles do. Such interconnected nanorods, when incorporated within nanofibers, have great potential to provide highly conductive pathways for energy applications, such as battery electrodes and separators. Symmetric BCP under cylindrical confinement with nanorod aspect ratio of 1, 5, and 10 are examined with three different types of nanorod-BCP attraction: a) neutral nanorod, b) A (wall-attractive phase)-attractive nanorods, and c) B (wall-repulsive phase)-attractive nanorods. As one may have expected, much less loading of longer nanorods are required to observe formation of radially and axially interconnected nanorods within the cylinder. The interconnected nanorods often, but not always, induce asymmetrical BCP morphology as well. From this trend, we were able to extract a dimensionless parameter, D/N, or the polymer domain diameter over the nanorod aspect ratio, to be correlated to the onset of nanorod interconnectivity and formation of asymmetrical BCP morphology. By developing a phase diagram with respect to D/N, one can predict the formation of desired BCP morphology, nanorod placement, and it connectivity within cylindrical confinement.