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Title: Evolution of the alkyl-chain dynamics in monolayer-protected gold clusters

Abstract

Alkyl-chain dynamics in monolayer protected metal cluster systems of gold have been studied by the quasielastic neutron scattering technique. Measurements have been carried out with 6, 12, and 18 carbon-long thiolate protected gold clusters of 4 nm core diameter. Dynamics of the monolayers in these systems, as indicated by the quasielastic broadening, were found to evolve continuously with increase in temperature from 270 to 400 K. Analysis of the elastic incoherent structure factor showed that while only a small portion of each chain is dynamically active at low temperature, the dynamics extend to almost the whole chain at 400 K. Although an improved model compared to our earlier reports, involving precessional motion of the chains on a cone is found to explain the observed data, a further improvement with reorientation of the chain around its axis with additional body axis fluctuation was most consistent with the experiment. The studies revealed the existence of complex dynamical motions of alkyl chains on the clusters. The studies suggest that repeated washings provide more space for the monolayer chains as a result of the removal of the phase transfer catalysts between the alkyl chains on the cluster surface. This provides space for greater orientationalmore » freedom, resulting in the observed dynamics even at lower temperatures.« less

Authors:
;  [1];  [2]; ;  [3]
  1. Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India)
  2. Institute Lau-Langevin, BP156, F-38042, Grenoble, Cedex 9 (France)
  3. DST Unit on Nanoscience, Department of Chemistry and Sophisticated Analytical Instrument Facility, Indian Institute of Technology Madras, Chennai 600 036 (India)
Publication Date:
OSTI Identifier:
20976702
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 7; Other Information: DOI: 10.1103/PhysRevB.75.075414; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; CARBON 18; CATALYSTS; CHAINS; CRYSTAL STRUCTURE; GOLD; NEUTRON DIFFRACTION; NEUTRON REACTIONS; ORGANIC COMPOUNDS; QUASI-ELASTIC SCATTERING; STRUCTURE FACTORS; SURFACE TREATMENTS; SURFACES; TEMPERATURE RANGE 0065-0273 K

Citation Formats

Mukhopadhyay, R., Mitra, S., Johnson, M., Rajeev Kumar, V. R., and Pradeep, T.. Evolution of the alkyl-chain dynamics in monolayer-protected gold clusters. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.075414.
Mukhopadhyay, R., Mitra, S., Johnson, M., Rajeev Kumar, V. R., & Pradeep, T.. Evolution of the alkyl-chain dynamics in monolayer-protected gold clusters. United States. doi:10.1103/PHYSREVB.75.075414.
Mukhopadhyay, R., Mitra, S., Johnson, M., Rajeev Kumar, V. R., and Pradeep, T.. Thu . "Evolution of the alkyl-chain dynamics in monolayer-protected gold clusters". United States. doi:10.1103/PHYSREVB.75.075414.
@article{osti_20976702,
title = {Evolution of the alkyl-chain dynamics in monolayer-protected gold clusters},
author = {Mukhopadhyay, R. and Mitra, S. and Johnson, M. and Rajeev Kumar, V. R. and Pradeep, T.},
abstractNote = {Alkyl-chain dynamics in monolayer protected metal cluster systems of gold have been studied by the quasielastic neutron scattering technique. Measurements have been carried out with 6, 12, and 18 carbon-long thiolate protected gold clusters of 4 nm core diameter. Dynamics of the monolayers in these systems, as indicated by the quasielastic broadening, were found to evolve continuously with increase in temperature from 270 to 400 K. Analysis of the elastic incoherent structure factor showed that while only a small portion of each chain is dynamically active at low temperature, the dynamics extend to almost the whole chain at 400 K. Although an improved model compared to our earlier reports, involving precessional motion of the chains on a cone is found to explain the observed data, a further improvement with reorientation of the chain around its axis with additional body axis fluctuation was most consistent with the experiment. The studies revealed the existence of complex dynamical motions of alkyl chains on the clusters. The studies suggest that repeated washings provide more space for the monolayer chains as a result of the removal of the phase transfer catalysts between the alkyl chains on the cluster surface. This provides space for greater orientational freedom, resulting in the observed dynamics even at lower temperatures.},
doi = {10.1103/PHYSREVB.75.075414},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 7,
volume = 75,
place = {United States},
year = {Thu Feb 15 00:00:00 EST 2007},
month = {Thu Feb 15 00:00:00 EST 2007}
}
  • Structural information on nanometer-sized gold particles has been limited, due in part to the problem of preparing homogeneous material. Here we report the crystallization and x-ray structure determination of a p-mercaptobenzoic acid (p-MBA)-protected gold nanoparticle, which comprises 102 gold atoms and 44 p-MBAs. The central gold atoms are packed in a Marks decahedron, surrounded by additional layers of gold atoms in unanticipated geometries. The p-MBAs interact not only with the gold but also with one another, forming a rigid surface layer. The particles are chiral, with the two enantiomers alternating in the crystal lattice. The discrete nature of the particlemore » may be explained by the closing of a 58-electron shell.« less
  • Monolayer-protected gold nanoparticle materials were synthesized and characterized for use as sorptive layers on chemical sensors. Thiols investigated as monolayer-forming molecules included dodecanethiol, benzenethiol, 4-chlorobenzenethiol, 4-bromobenzenethiol, 4-trifluoromethylbenzenethiol, 4-hydroxybenzenethiol, and 4-aminobenzenethiol. Films of selected monolayer protected nanoparticle (MPN) materials were deposited on thickness shear mode (TSM) devices and vapor uptake properties were measured at 298K. Many, but not all, PMN-based sensing layers demonstrated rapid and reversible uptake of vapors, and sorptive selectivity varies with the monolayer structure. The mass of vapor sorbed per mass of sorptive material was determined and compared with sorptive polymers. Estimated partition coefficients of the MPN materialsmore » are comparable to those of polymer layers. To the extent that MPN-coated chemiresistor vapor sensors give lower detection limits than polymer-coated vapor sensors such as surface acoustic wave vapor sensors, as has been reported, such performance likely results from better signal-to-noise per sorbed vapor molecule rather than greater vapor sorption by the MPN materials.« less
  • The application of a dodecanethiol monolayer protected gold nanoparticle (MPN) stationary phase within a microchannel environment was explored using a square capillary column as a model for a high-speed, microfabricated gas chromatography (?GC). Successful deposition and evaluation of a dodecanethiol MPN phase within a 1.3 m long, 100?m by 100?m square capillary is reported. Depth of the MPN phase was evaluated using SEM analysis. An average thickness of 15 nm along the capillary walls was determined. While the film depth along the walls was very uniform, the corner depths were greater with the largest observed depth being 430 nm. Overall,more » an efficient chromatographic system was obtained with a minimum reduced plate height, hmin, of 1.2 for octane (k= 0.22). Characterization of the MPN column was completed using four compound classes (alkanes, alcohols, ketones, and aromatics) that were used to form a 7 component mixture with a 2 second separation. A mixture consisting of a nerve agent simulator in a sample containing analytes that may commonly interfere with detection was also separated in 2 seconds, much faster than a similar separation previously reported using a?GC system in 50 seconds. Application of the square capillary MPN column for a high-speed separation as the second column of a comprehensive two-dimensional gas chromatography system (GC x GC) was also explored. Comparison of the MPN stationary phase was compared to phases employed in previously reported?GC systems.« less
  • The use of a thin film of monolayer protected gold nanoparticles (MPNs) as a stationary phase for gas chromatography (GC) is reported. Dodecanethiol-protected gold nanoparticles were prepared and characterized. Deposition of a MPN film was successfully completed within a 2 m, 530 {micro}m (i.d.) deactivated silica capillary using gravity to force a plug of solution containing the MPN material through the capillary for deposition. The presence of a thin MPN film on the GC capillary inside wall was confirmed with SEM analysis with an average film thickness of 60.7 nm measured. The retention behavior of the dodecanethiol MPN stationary phasemore » was studied using four different classes of compounds (alkanes, alcohols, aromatics and ketones) and their retention orders were compared to a commercially available column (AT-1, 100 nm phase thickness). The separation of an eight-component mixture was performed using both isothermal and temperature programming separation methods with the novel dodecanethiol MPN phase. The isothermal separation was then objectively compared to the commercial AT-1 stationary phase column using the same experimental parameters. The commercial column had an efficiency, N, of 6200 (k{prime} = 0.33) while the dodecanethiol MPN stationary phase had an efficiency, N, of 5700 (k{prime} = 0.21) for the same analyte, octane. The reduced plate height, h, for this same analyte was found to be less than 1 at the optimum linear flow velocity. Based upon the efficiencies and reduced plate height studies as a function of linear flow velocity, we conclude that the MPN stationary phase operated at nearly the optimum possible performance level. The robustness of the MPN phase is also discussed with consistent performance observed over several months. Overall, the use of monolayer protected gold nanoparticles as gas chromatographic stationary phase materials appears promising.« less