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Molecular Dynamics Simulations of Dodecanethiol Coated Gold Nanoparticles on Organic Liquid Toluene

Poddar, Nitun Nirjhar
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1382821849

Abstract Details

2013, Master of Science in Engineering, University of Toledo, College of Engineering.
Colloidal gold nanoparticles may be used in a variety of applications ranging from solar cells to sensors to catalysis and drug delivery. In particular, ordered gold nanoparticle thin-films have been proposed as efficient coupling layers which may be used to maximize the efficiency of photovoltaic solar cells. In addition, recently a drop-drying method to self-assemble a well-ordered monolayer of Au nanoparticles has been developed. In this method, a monodisperse solution of gold nanoparticles whose size has been selected via chemical synthesis, and which are coated with organic ligands to prevent aggregation and precipitation is used. Using this method a monolayer of Au nanoparticles can be made that covers the full area of a 2” silicon wafer. However, the interaction between the gold nanoparticles and the interface, which plays a key role in determining the film-quality, is not well understood. One of the main objectives of the work presented in this thesis is to obtain a better fundamental understanding of the structure and interactions of ligand-coated Au nanoparticles at a solvent-vapor interface. In particular, motivated by experimental and simulation results, we have carried out extensive molecular dynamics simulations of dodecanethiol (DDT)-coated Au nanoparticles in both bulk toluene and at the toluene-vapor interface. Our simulations were carried out using the public domain software LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) along with the OPLS (Optimized Potential for Liquid Simulation) force field which is a force-field which has been specifically developed for simulating organic liquids. Our simulations indicate that, in contrast to previous simulations of decanethiol and octadecanethiol coated Au nanoparticles in water, the dodecanethiol-coated nanoparticle (NP) sits relatively low in the toluene, such that the Au core never penetrates above the interface, while the thiols only partially stick out above the interface. Somewhat surprisingly, we also found that the nanoparticle is not spherical at the interface, but instead the nanoparticle width is larger than the nanoparticle height. Both of these results may be explained by the fact that the nanoparticle ligands are attracted to toluene. Due to this attraction, the ligands above the NP core, which stick out above the interface, are more compressed than those on the side or bottom which extend into liquid toluene. These results also indicate that the nanoparticle rolling mechanism, which has been observed in other experiments and which may greatly enhance the diffusivity of Au nanoparticles during the island self-assembly process, does not apply in this case. In addition to determining the nanoparticle position and shape at the interface, we have also determined the interfacial adsorption energy for a nanoparticle at the interface. The resulting relatively large value for the binding energy was found to be consistent with experimental results for nanoparticle island-growth with high excess thiol concentration, for which a diffusion length (corresponding to the distance a nanoparticle can diffuse before leaving the interface and returning to solution due to thermal fluctuations) much larger than the inter-island spacing was observed. By comparing the radial toluene density near the nanoparticle at the interface with that near the nanoparticle in bulk, and also taking into account the particle position with respect to the interface, the van der Waals corrections to the binding energy were also calculated. Since diffusion plays an important role in in drop-drying, we have also calculated the diffusion coefficient for DDT-coated Au NP at the toluene-vapor interface. Somewhat surprisingly, we find that - perhaps due to the fact that the nanoparticle is almost fully submerged - the two-dimensional diffusion coefficient at the toluene-vapor interface is in good agreement with the Stokes-Einstein prediction for 3D bulk diffusion.
Jacques Amar (Committee Chair)
Mohammed Niamat (Committee Member)
Gursel Serpen (Committee Member)
114 p.
Computer Science; Condensed Matter Physics; Physics
Molecular Dynamics Simulation, Dodecanethiol, Gold nanoparticles, Toluene

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Citations

  • Poddar, N. N. (2013). Molecular Dynamics Simulations of Dodecanethiol Coated Gold Nanoparticles on Organic Liquid Toluene [Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1382821849

    APA Style (7th edition)

  • Poddar, Nitun. Molecular Dynamics Simulations of Dodecanethiol Coated Gold Nanoparticles on Organic Liquid Toluene. 2013. University of Toledo, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1382821849.

    MLA Style (8th edition)

  • Poddar, Nitun. "Molecular Dynamics Simulations of Dodecanethiol Coated Gold Nanoparticles on Organic Liquid Toluene." Master's thesis, University of Toledo, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1382821849

    Chicago Manual of Style (17th edition)

toledo1382821849
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© 2013, all rights reserved.
This open access ETD is published by University of Toledo and OhioLINK.