Oligocorannulenes are polyarenes composed of several corannulene units that are covalently linked. Their behavior arises both from the diverse properties of each corannulenyl unit and from the interactions between them. In this paper, we present the synthesis, stereochemistry, reduction, and self-assembly properties of a novel type of oligocorannulene: branched 1,3,5-tricorannulenylbenzene. Several stereodynamical elements combine to give rich stereochemistry: bowl-to-bowl inversion, rotation about the aryl-aryl single bonds, and residual stereoisomerism of molecular propellers. Reduction with lithium metal yields an intermediate hexaanion and ultimately produces a highly charged dodecaanion. Self-diffusion NMR demonstrates that the dodecaanion undergoes supramolecular dimerization through charged polyarene stacking, wherein two molecules are linked at all three contact points. The preference for dimerization over dendrimerization is attributed to an entropic effect. The dimer is found to undergo complex structural dynamics, as well as ion-pairing dynamics, as revealed by variable-temperature 1H- and 7Li-NMR. Copyright (C) 2012 John Wiley & Sons, Ltd.

Dodecanethiol-capped gold nanoparticles (NPs) deposited onto a poly(ethylene glycol) substrate quickly coarsen over a timescale of days when stored under ambient conditions. The NP coarsening was studied at different surface coverages and temperatures. The coarsening of NPs depended on their location on the film; NPs located inside the channels coarsened in a different fashion than NPs deposited on the plateaus. Size distributions studied by image analysis and comparison to theoretical distribution functions shed light on the coarsening mechanism in each case, revealing the role of dimensionality.

External electric fields readily align birefringent block-copolymer mesophases. In this study the effect of gold nanoparticles on the electric-field-induced alignment of a lamellae-forming polystyrene-block-poly(2-vinylpyridine) copolymer is assessed. Nanoparticles are homogeneously dispersed in the styrenic phase and promote the quantitative alignment of lamellar domains by substantially lowering the critical field strength above which alignment proceeds. The results suggest that the electric-field-assisted alignment of nanostructured block copolymer/nanoparticle composites may offer a simple way to greatly mitigate structural and orientational defects of such films under benign experimental conditions.

We investigate the kinetics of block copolymer/nanoparticle composite alignment in an electric field using in situ transmission small-angle X-ray scattering. As a model system, we employ a lamellae forming polystyrene-block-poly(2-vinyl pyridine) block copolymer with different contents of gold nanoparticles in thick films under solvent vapor annealing. While the alignment improves with increasing nanoparticle fraction, the kinetics slows down. This is explained by changes in the degree of phase separation and viscosity. Our findings provide extended insights into the basics of nanocomposite alignment.

Tailoring the size and surface chemistry of nanoparticles allows one to control their position in a block copolymer, but this is usually limited to one-dimensional distribution across domains. Here, the hierarchical assembly of poly(ethylene oxide)-stabilized gold nanoparticles (Au-PEO) into hexagonally packed clusters inside mesostructured ultrathin films of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is described. A close examination of the structural evolution at different nanoparticle filling fractions and PEO ligand molecular weights suggests that the mechanism leading to this structure-within-structure is the existence of two phase separation processes operating on different time scales. The length of the PEO ligand is shown to influence not only the interparticle distances but also the phase separation processes. These conclusions are supported by novel mesoscopic simulations, which provide additional insight into the kinetic and thermodynamic factors that are responsible for this behavior.