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Volume 125, 2004
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Adaptive chemistry of bifunctional gold nanoparticles at the air/water interface. A synchrotron X-ray study of giant amphiphiles

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Abstract

A series of ligand stabilized gold nanoparticles with diameters close to 3 nm were studied as Langmuir monolayers at the air/water interface by synchrotron X-ray diffraction and reflectivity. Alkylthiols with different length and/or terminal functional group (hydrophilic or hydrophobic) were introduced into the ligand shell by ligand place exchange reactions. Synchrotron grazing incidence X-ray diffraction (GIXD) and specular X-ray reflectivity reveal the well known hexagonally packed monolayers. In addition the mixed hydrophilic/hydrophobic ligand shell nanoparticles show a high degree of environmental responsiveness, as they adapt to an amphiphilic distribution of ligands around the gold core when spread at the water surface. Likewise nanoparticles of mixed long and short alkyl chains respond to lateral pressure by adopting a structure where the short alkyl chains determine the nearest neighbor distance while the long alkyl chains determine the film thickness. Based on X-ray reflectivity measurements, which quantitatively account for the electron density in the monolayers, combined with GIXD we calculate the average size and number of atoms of the individual gold particle cores, and estimate the number of passivating ligand on the particle surface. Typical values are dAu-core = 16 Å, dnanoparticle = 26–37 Å depending on the ligands, MW = 30–40 000 g mol−1, number of ligands = 40–60. The thickness of the monolayers was determined by AFM after transfer of the monolayers to a solid support using the Langmuir–Schaefer technique. The combination of the different techniques produce a very consistent picture of the structure and adaptive chemical nature of the nanoparticles studied, and reveal a surprisingly monodisperse particle distribution centered around 140 atoms in the gold core.

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Publication details

The article was received on 18 Mar 2003, accepted on 03 Apr 2003 and first published on 24 Oct 2003


Article type: Paper
DOI: 10.1039/B303117A
Citation: Faraday Discuss., 2004,125, 221-233
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    Adaptive chemistry of bifunctional gold nanoparticles at the air/water interface. A synchrotron X-ray study of giant amphiphiles

    K. Nørgaard, M. J. Weygand, K. Kjaer, M. Brust and T. Bjørnholm, Faraday Discuss., 2004, 125, 221
    DOI: 10.1039/B303117A

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