| 123 |
|
Garde and coworkers\cite{garde:nl2005,garde:PhysRevLett2009} applied |
| 124 |
|
this approach to various liquid interfaces and studied how thermal |
| 125 |
|
conductance (or resistance) is dependent on chemical details of a |
| 126 |
< |
number of hydrophobic and hydrophilic aqueous interfaces. |
| 126 |
> |
number of hydrophobic and hydrophilic aqueous interfaces. {\bf And |
| 127 |
> |
Luo {\it et al.} studied the thermal conductance of Au-SAM-Au |
| 128 |
> |
junctions using the same approach, with comparison to a constant |
| 129 |
> |
temperature difference method\cite{Luo20101}. While this latter |
| 130 |
> |
approach establishes more thermal distributions compared to the |
| 131 |
> |
former RNEMD methods, it does not guarantee momentum or kinetic |
| 132 |
> |
energy conservations.} |
| 133 |
|
|
| 134 |
|
Recently, we have developed a Non-Isotropic Velocity Scaling (NIVS) |
| 135 |
|
algorithm for RNEMD simulations\cite{kuang:164101}. This algorithm |
| 143 |
|
The work presented here deals with the Au(111) surface covered to |
| 144 |
|
varying degrees by butanethiol, a capping agent with short carbon |
| 145 |
|
chain, and solvated with organic solvents of different molecular |
| 146 |
< |
properties. Different models were used for both the capping agent and |
| 147 |
< |
the solvent force field parameters. Using the NIVS algorithm, the |
| 148 |
< |
thermal transport across these interfaces was studied and the |
| 149 |
< |
underlying mechanism for the phenomena was investigated. |
| 146 |
> |
properties. {\bf To our knowledge, few previous MD inverstigations |
| 147 |
> |
have been found to address to these systems yet.} Different models |
| 148 |
> |
were used for both the capping agent and the solvent force field |
| 149 |
> |
parameters. Using the NIVS algorithm, the thermal transport across |
| 150 |
> |
these interfaces was studied and the underlying mechanism for the |
| 151 |
> |
phenomena was investigated. |
| 152 |
|
|
| 153 |
|
\section{Methodology} |
| 154 |
|
\subsection{Imposed-Flux Methods in MD Simulations} |
| 844 |
|
surfaces 90\% covered by butanethiols, but did not see this above |
| 845 |
|
phenomena even at $\langle T\rangle\sim$300K. That said, we did |
| 846 |
|
observe butanethiols migrating to neighboring three-fold sites during |
| 847 |
< |
a simulation. Since the interface persisted in these simulations, |
| 847 |
> |
a simulation. Since the interface persisted in these simulations, we |
| 848 |
|
were able to obtain $G$'s for these interfaces even at a relatively |
| 849 |
|
high temperature without being affected by surface reconstructions. |
| 850 |
|
|
| 888 |
|
surface Au layer to the capping agents. Therefore, in our simulations, |
| 889 |
|
the Au / S interfaces do not appear to be the primary barrier to |
| 890 |
|
thermal transport when compared with the butanethiol / solvent |
| 891 |
< |
interfaces. |
| 891 |
> |
interfaces. {\bf This confirms the results from Luo {\it et |
| 892 |
> |
al.}\cite{Luo20101}, which reported $G$ for Au-SAM junctions |
| 893 |
> |
generally twice larger than what we have computed for the |
| 894 |
> |
thiol-liquid interfaces.} |
| 895 |
|
|
| 896 |
|
\begin{figure} |
| 897 |
|
\includegraphics[width=\linewidth]{vibration} |
| 917 |
|
vibrations were treated classically. The presence of extra degrees of |
| 918 |
|
freedom in the AA force field yields higher heat exchange rates |
| 919 |
|
between the two phases and results in a much higher conductivity than |
| 920 |
< |
in the UA force field. |
| 920 |
> |
in the UA force field. {\bf Due to the classical models used, this |
| 921 |
> |
even includes those high frequency modes which should be unpopulated |
| 922 |
> |
at our relatively low temperatures. This artifact causes high |
| 923 |
> |
frequency vibrations accountable for thermal transport in classical |
| 924 |
> |
MD simulations.} |
| 925 |
|
|
| 926 |
|
The similarity in the vibrational modes available to solvent and |
| 927 |
|
capping agent can be reduced by deuterating one of the two components |
| 1026 |
|
Foundation under grant CHE-0848243. Computational time was provided by |
| 1027 |
|
the Center for Research Computing (CRC) at the University of Notre |
| 1028 |
|
Dame. |
| 1029 |
+ |
|
| 1030 |
+ |
\section{Supporting Information} |
| 1031 |
+ |
This information is available free of charge via the Internet at |
| 1032 |
+ |
http://pubs.acs.org. |
| 1033 |
+ |
|
| 1034 |
|
\newpage |
| 1035 |
|
|
| 1036 |
|
\bibliography{interfacial} |
