Controlled hierarchical assembly of gold nanoparticles in macroscopic films: from densely packed monolayers to networks of micropores and nanobundlesElectronic supplementary information (ESI) available. See DOI: 10.1039/c6sm02586b

• Main Authors: Gravelsins, Steven, Hasham, Minhal, Lin, Yi, Yu, Kevin, Tie, Monique, Goh, Cynthia, Dhirani, Al-Amin
• Format: Article
• Language: English
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/c6sm02586b

The present study demonstrates the ability of excess, weakly amphiphilic n -alkanethiols ( n = 4, 12, 18) and solvent composition to tune through a wide range of large-scale, macroscopic architectures formed by alkanethiol-capped Au nanoparticles (NPs). Both the alkanethiols and NPs are significantly hydrophobic species and compete for surface area at an air-water interface. When solutions of the two species are spread on a large (50 cm 2 ) water surface in a Teflon well, a thin film forms and exhibits co-existing macroscopic regions with various distinct NP self-assembled architectures, namely a close packed monolayer, a network phase characterized by micron-sized pores (micropores) surrounded by quasi-linear bundles of nanoparticles, and finally aggregates. We hypothesize that the co-existence of various NP architectures results from fast, non-uniform evaporation across the large water surface. When solutions are instead deposited on a smaller (5 cm 2 ) water surface contained within a Teflon ring to control the water surface curvature and the evaporation rate is slowed, we show for the first time that NPs form macroscopically uniform self-assemblies whose architectures can be tuned from monolayers → monolayers with micropores → extended micropore/NP bundle networks by varying excess alkanethiol concentration and solvent composition. We propose that competition between NPs and excess alkanethiols for water surface area, and alkanethiol self-assembly as well as solvent dewetting play important roles in the formation of the network phase, and discuss a potential mechanism for its formation. Hydrophobic gold nanoparticles and excess alkanethiols self-assemble forming extensive pore/bundle networks at the air-water interface.