title: Effects of surfactant concentration on formation of high-aspect-ratio gold nanorods.
abstract: The effects of surfactant concentration in a growth solution on the elongation of gold nanorods were examined. Gold nanorods were synthesized in solutions with different concentrations of hexadecyltrimethylammonium bromide (HTAB): 100, 200, 300, 400, 500, and 600 mM. The nanorods grown in a solution with higher surfactant concentrations were longer (aspect ratio ~30) than those grown in that with lower concentrations (aspect ratio <10). The self-assembled surfactant structures in the solutions were analyzed using viscosity measurement and small-angle X-ray scattering. These results showed a decrease in the inter-micellar distance with increasing surfactant concentration. Taking the chemical equilibrium for the complex formation between Au ions and HTAB micelles into account, we found that the free Au ion concentration decreases accompanied with the increase in the surfactant concentration. This decrease in the free Au ion concentration suppresses undesirable secondary nucleation of gold crystals in a growth solution, resulting in gold nanorod elongation.
authors.affiliation: Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8565, Japan. takenaka.yoshiko@aist.go.jp
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Takenaka
authors.forename: Youhei
authors.initials: Y
authors.lastname: Kawabata
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kitahata
authors.forename: Masaru
authors.initials: M
authors.lastname: Yoshida
authors.forename: Yoko
authors.initials: Y
authors.lastname: Matsuzawa
authors.forename: Takuya
authors.initials: T
authors.lastname: Ohzono
keywords: Hexadecyltrimethylammonium bromide (HTAB); High-aspect-ratio gold nanorod; Micellar structure; Secondary nucleation; Small-angle X-ray scattering (SAXS)