Controllable end-to-end alignment of nanorods in polymer films would enable new applications, especially for metallic nanorods, where coupling of surface plasmon resonances can lead to enhanced electric fields (hot spots) between nanorod ends. To achieve end-to-end alignment, we investigate the dispersion and aggregation behavior of polymer brush-coated nanorods in a chemically identical homopolymer matrix using self-consistent field theory (SCFT). We find good agreement with previous DFT calculations and experiments for side-by-side alignment. However, we also find that thermodynamic aggregation of uniformly grafted nanorods in a polymer matrix will preferentially occur side-by-side rather than end-to-end. To achieve preferential end-to-end linking, we propose using different grafting molecular weights (relative to the length of the matrix chains) on the sides and the ends of the nanorods. We demonstrate this idea with an example system in which the side brush length is chosen so that the side-by-side interaction energy is purely repulsive, while the end grafted polymer chains are shorter so that the end-to-end interaction energy has a strong attractive well due to autophobic dewetting effects. We thus show that using chemically similar brushes with different molecular weights on the sides and ends of the nanorods can lead to entropically driven end-linked nanorods in an organic matrix. The gap between the nanorod ends is tunable by changing the end brush molecular weight, and therefore the plasmon enhancement would also be tunable.
Triblock amphiphilic molecules composed of three distinct segments provide a large parameter space to obtain self-assembled structures beyond what is achievable with conventional amphiphiles. To obtain a molecular understanding of the thermodynamics of self-assembly, we develop a coarse-grained triblock polymer model and apply self-consistent field theory to investigate the packing mechanism into layer structures. By tuning the structural and interaction asymmetry, we are able to obtain bilayers and monolayers, where the latter may additionally be mixed (symmetric) or segregated (asymmetric). Of particular interest for a variety of applications are the asymmetric monolayers, where segregation of end blocks to opposite surfaces is expected to have important implications for the development of functional nanotubes and vesicles with distinct surface chemistries.