| 33 |
|
\newcolumntype{A}{p{1.5in}} |
| 34 |
|
\newcolumntype{B}{p{0.75in}} |
| 35 |
|
|
| 36 |
< |
\title{Simulations of heat conduction at thiolate-capped gold |
| 37 |
< |
surfaces: The role of chain length and solvent penetration} |
| 36 |
> |
\title{Simulations of Heat Conduction at Thiolate-Capped Gold |
| 37 |
> |
Surfaces: The Role of Chain Length and Solvent Penetration} |
| 38 |
|
|
| 39 |
|
\author{Kelsey M. Stocker and J. Daniel |
| 40 |
|
Gezelter\footnote{Corresponding author. \ Electronic mail: |
| 116 |
|
interfaces, epitaxial TiN/single crystal oxide interfaces, and |
| 117 |
|
hydrophilic and hydrophobic interfaces between water and solids with |
| 118 |
|
different self-assembled |
| 119 |
< |
monolayers.\cite{cahill:793,Wilson:2002uq,PhysRevB.67.054302,doi:10.1021/jp048375k,PhysRevLett.96.186101} |
| 120 |
< |
Wang {\it et al.} studied heat transport through long-chain |
| 121 |
< |
hydrocarbon monolayers on gold substrate at the individual molecular |
| 122 |
< |
level,\cite{Wang10082007} Schmidt {\it et al.} studied the role of |
| 119 |
> |
monolayers.\cite{cahill:793,Wilson:2002uq,PhysRevB.67.054302,doi:10.1021/jp048375k,PhysRevLett.96.186101} Schmidt {\it et al.} studied the role of |
| 120 |
|
cetyltrimethylammonium bromide (CTAB) on the thermal transport between |
| 121 |
< |
gold nanorods and solvent,\cite{doi:10.1021/jp8051888} and Juv\'e {\it |
| 122 |
< |
et al.} studied the cooling dynamics, which is controlled by thermal |
| 123 |
< |
interface resistance of glass-embedded metal |
| 124 |
< |
nanoparticles.\cite{PhysRevB.80.195406} Although interfaces are |
| 121 |
> |
gold nanorods and solvent.\cite{doi:10.1021/jp8051888} |
| 122 |
> |
Wang {\it et al.} studied heat transport through long-chain |
| 123 |
> |
hydrocarbon monolayers on unsolvated gold substrate at the individual molecular |
| 124 |
> |
level.\cite{Wang10082007} The introduction of solvent adds yet another interface and potential barrier for heat transfer. Juv\'e {\it |
| 125 |
> |
et al.} studied the cooling dynamics of glass-embedded nanoparticles, which is controlled by thermal |
| 126 |
> |
interfacial resistance and heat diffusion in the matrix.\cite{PhysRevB.80.195406} Hartland also notes the importance of heat transfer through diffusive solvent behavior.\cite{hartland2011} Although interfaces are |
| 127 |
|
normally considered barriers for heat transport, Alper {\it et al.} |
| 128 |
|
have suggested that specific ligands (capping agents) could completely |
| 129 |
|
eliminate this barrier |
| 368 |
|
solvent interface extends a significant distance from the metal |
| 369 |
|
surface, the interfacial resistance $R_K$ can be computed by |
| 370 |
|
summing a series of temperature drops between adjacent temperature |
| 371 |
< |
bins along the $z$ axis.} |
| 371 |
> |
bins along the $z$ axis. The depicted temperature profile is from a RNEMD simulation of 100\% butanethiolate (C$_4$) coverage.} |
| 372 |
|
\label{fig:resistor_series} |
| 373 |
|
\end{figure} |
| 374 |
|
|
| 500 |
|
|
| 501 |
|
\begin{figure} |
| 502 |
|
\includegraphics[width=\linewidth]{figures/timelapse} |
| 503 |
< |
\caption{Images of 25\%~C$_4$~/~75\%~C$_{12}$ (top panel) and 75\%~C$_4$~/~25\%~C$_{12}$ (bottom panel) interfaces at the beginning and end of 3 ns simulations. Solvent molecules that were initially present in the thiolate layer are colored light blue. Diffusion of the initially-trapped solvent into the bulk is apparent in the interface with fewer long chains. Trapped solvent is orientationally locked to the ordered ligands (and is less able to diffuse into the bulk) when the fraction of long chains increases.} |
| 503 |
> |
\caption{Images of 75\%~C$_4$~/~25\%~C$_{12}$ (top panel) and 25\%~C$_4$~/~75\%~C$_{12}$ (bottom panel) interfaces at the beginning and end of 3 ns simulations. Solvent molecules that were initially present in the thiolate layer are colored light blue. Diffusion of the initially-trapped solvent into the bulk is apparent in the interface with fewer long chains. Trapped solvent is orientationally locked to the ordered ligands (and is less able to diffuse into the bulk) when the fraction of long chains increases.} |
| 504 |
|
\label{fig:timelapse} |
| 505 |
|
\end{figure} |
| 506 |
|
|
| 583 |
|
Previous simulations have demonstrated non-monotonic behavior for $G$ as a function of the surface coverage. One difficulty with the previous study was the ability of butanethiolate ligands to migrate on the Au(111) surface and to form segregated domains. To simulate the effect of low coverages while preventing thiolate domain formation, we maintain 100\% thiolate coverage while varying the proportions of short (butanethiolate, C$_4$) and long (decanethiolate, C$_{10}$, or dodecanethiolate, C$_{12}$) alkyl chains. Data on the conductance trend as the fraction of long chains was varied is shown in figure \ref{fig:Gstacks}. Note that as in the previous study, $G$ is dependent upon solvent accessibility to thermally excited ligands. Our simulations indicate a similar (but less dramatic) non-monotonic dependence on the fraction of long chains. |
| 584 |
|
\begin{figure} |
| 585 |
|
\includegraphics[width=\linewidth]{figures/Gstacks} |
| 586 |
< |
\caption{Interfacial thermal conductivity of mixed-chains has a non-monotonic dependence on the fraction of long chains (lower panels). At low fractions of long chains, the solvent escape rate ($k_{escape}$) dominates the heat transfer process, while the solvent-thiolate orientational ordering dominates in systems with higher fractions of long chains (upper panels).} |
| 586 |
> |
\caption{Interfacial thermal conductivity of mixed-chains has a non-monotonic dependence on the fraction of long chains (lower panels). At low fractions of long chains, the solvent escape rate ($k_{escape}$) dominates the heat transfer process, while the solvent-thiolate orientational ordering ($<d>$) dominates in systems with higher fractions of long chains (upper panels).} |
| 587 |
|
\label{fig:Gstacks} |
| 588 |
|
\end{figure} |
| 589 |
|
|
| 718 |
|
|
| 719 |
|
\bibliography{thiolsRNEMD} |
| 720 |
|
|
| 721 |
+ |
\newpage |
| 722 |
+ |
|
| 723 |
+ |
\begin{figure} |
| 724 |
+ |
\centering{\includegraphics{figures/toc2}} |
| 725 |
+ |
\caption{Images of 75\%~C$_4$~/~25\%~C$_{12}$ (top panel) and 25\%~C$_4$~/~75\%~C$_{12}$ (bottom panel) interfaces at the beginning and end of 3 ns simulations. Solvent molecules that were initially present in the thiolate layer are colored light blue. Diffusion of the initially-trapped solvent into the bulk is apparent in the interface with fewer long chains. Trapped solvent is orientationally locked to the ordered ligands (and is less able to diffuse into the bulk) when the fraction of long chains increases.} |
| 726 |
+ |
\label{fig:toc} |
| 727 |
+ |
\end{figure} |
| 728 |
+ |
|
| 729 |
|
\end{doublespace} |
| 730 |
|
\end{document} |
| 731 |
|
|
