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Thermal transport coefficients, notably the interfacial thermal conductance, were determined in planar and spherical gold interfaces functionalized with CTAB (cetyltrimethylammonium bromide) or MTAB (16-mercapto-hexadecyl-trimethylammonium bromide) using reverse non-equilibrium molecular dynamics (RNEMD) methods. The systems of interest included (111), (110), and (100) planar facets as well as nanospheres (r = 10 Å). The effect of metal polarizability was investigated through the implementation of the density-readjusted embedded atom model (DR-EAM), a polarizable metal potential. We find that conductance is higher in MTAB-capped interfaces, due in large part to the metal-to-ligand coupling provided by the Au-S bond. Alternatively, CTAB does not couple strongly with either the metal or the solvent, and it is largely a barrier to heat transfer, resulting in a much lower interfacial thermal conductance. Through analysis of physical contact between the ligand and the solvent, we find that there is significantly more overlap in the MTAB systems than the CTAB systems, mirroring the trends we observed in the conductance.
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Bromide Causes Facet-Selective Atomic Addition in Gold Nanorod Syntheses
The aspect ratio-dependent properties of gold nanorods are used in a variety of applications, but the cause of anisotropic nanorod growth remains unclear. Measurements utilizing single-crystal electrodes were collected to determine what additive(s) in pentatwinned gold nanorod syntheses are responsible for facet-selective atomic addition. With cetyltrimethylammonium in the absence of bromide, the rate of atomic addition to Au(100) and Au(111) single crystals was the same, and isotropic nanoparticles were produced. The addition of increasing concentrations of bromide suppressed the rate of atomic addition to Au(100) relative to Au(111) and increased the aspect ratio of gold nanorods. Bromide was a more effective passivator of Au(100) in the absence of cetyltrimethylammonium, indicating cetyltrimethylammonium does not cause facet-selective atomic addition. Cetyltrimethylammonium surfactant is still necessary for gold nanorod growth because it reduces the rate of gold ion reduction and stabilizes suspended nanoparticles against aggregation.
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- Award ID(s):
- 1808108
- PAR ID:
- 10168596
- Date Published:
- Journal Name:
- Chemistry of Materials
- ISSN:
- 0897-4756
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.chemmater.0c01494
