Directing close-packing of midnanosized gold nanoparticles at a water/hexane interface

This paper reports a method for assembling midnanosized Au nanoparticles (25 < d < 100 nm) into close-packed 2D arrays with a high degree of local order. An in situ coating of An nanoparticles with an alkanethiol surfactant can induce close-packed particle arrays when the nanoparticles are trapped at the interface. The film morphology was determined to be either monoparticulate or multiparticulate depending on the I-dodecanethiol concentration. This paper reports on the optimum conditions for the formation of a close-packed 2D array by suggesting a phase diagram obtained from a plot of the I-dodecanethiol concentration versus the nanoparticle diameter. When the diameter of Au nanoparticles was larger than ca. 40 nm, the full coverage of 1-dodecanethiols on the surface of nanoparticles was not enough to form close-packed nanoparticle arrays. The larger nanoparticles required the more 1-dodecanethiols to form a close-packed 2D array. This method also allows the nanoparticle surface to be coated asymmetrically with 1-dodecanethiols, which was confirmed qualitatively from contact angle measurements.