1 |
% ****** Start of file aipsamp.tex ****** |
2 |
% |
3 |
% This file is part of the AIP files in the AIP distribution for REVTeX 4. |
4 |
% Version 4.1 of REVTeX, October 2009 |
5 |
% |
6 |
% Copyright (c) 2009 American Institute of Physics. |
7 |
% |
8 |
% See the AIP README file for restrictions and more information. |
9 |
% |
10 |
% TeX'ing this file requires that you have AMS-LaTeX 2.0 installed |
11 |
% as well as the rest of the prerequisites for REVTeX 4.1 |
12 |
% |
13 |
% It also requires running BibTeX. The commands are as follows: |
14 |
% |
15 |
% 1) latex aipsamp |
16 |
% 2) bibtex aipsamp |
17 |
% 3) latex aipsamp |
18 |
% 4) latex aipsamp |
19 |
% |
20 |
% Use this file as a source of example code for your aip document. |
21 |
% Use the file aiptemplate.tex as a template for your document. |
22 |
\documentclass[% |
23 |
aip,jcp, |
24 |
amsmath,amssymb, |
25 |
preprint,% |
26 |
% reprint,% |
27 |
%author-year,% |
28 |
%author-numerical,% |
29 |
jcp]{revtex4-1} |
30 |
|
31 |
\usepackage{graphicx}% Include figure files |
32 |
\usepackage{dcolumn}% Align table columns on decimal point |
33 |
%\usepackage{bm}% bold math |
34 |
\usepackage{times} |
35 |
\usepackage[version=3]{mhchem} % this is a great package for formatting chemical reactions |
36 |
\usepackage{url} |
37 |
|
38 |
\begin{document} |
39 |
|
40 |
\title{Friction at Water / Ice-I$_\mathrm{h}$ interfaces: Do the |
41 |
Facets of Ice Have Different Hydrophilicity?} |
42 |
|
43 |
\author{Patrick B. Louden} |
44 |
|
45 |
\author{J. Daniel Gezelter} |
46 |
\email{gezelter@nd.edu.} |
47 |
\affiliation{Department of Chemistry and Biochemistry, University |
48 |
of Notre Dame, Notre Dame, IN 46556} |
49 |
|
50 |
\date{\today} |
51 |
|
52 |
\begin{abstract} |
53 |
Abstract abstract abstract... |
54 |
\end{abstract} |
55 |
|
56 |
\maketitle |
57 |
|
58 |
\section{Introduction} |
59 |
Explain a little bit about ice Ih, point group stuff. |
60 |
|
61 |
Mention previous work done / on going work by other people. Haymet and Rick |
62 |
seem to be investigating how the interfaces is perturbed by the presence of |
63 |
ions. This is the conlcusion of a recent publication of the basal and |
64 |
prismatic facets of ice Ih, now presenting the pyramidal and secondary |
65 |
prism facets under shear. |
66 |
|
67 |
\section{Methodology} |
68 |
|
69 |
\begin{figure} |
70 |
\includegraphics[width=\linewidth]{SP_comic_strip} |
71 |
\caption{\label{fig:spComic} The secondary prism interface with a shear |
72 |
rate of 3.5 ms\textsuperscript{-1}. Lower panel: the local tetrahedral order |
73 |
parameter, $q(z)$, (black circles) and the hyperbolic tangent fit (red line). |
74 |
Middle panel: the imposed thermal gradient required to maintain a fixed |
75 |
interfacial temperature. Upper panel: the transverse velocity gradient that |
76 |
develops in response to an imposed momentum flux. The vertical dotted lines |
77 |
indicate the locations of the midpoints of the two interfaces.} |
78 |
\end{figure} |
79 |
|
80 |
\begin{figure} |
81 |
\includegraphics[width=\linewidth]{Pyr_comic_strip} |
82 |
\caption{\label{fig:pyrComic} The pyramidal interface with a shear rate of 3.8 \ |
83 |
ms\textsuperscript{-1}. Panel descriptions match those in figure \ref{fig:spComic}.} |
84 |
\end{figure} |
85 |
|
86 |
\subsection{Pyramidal and secondary prism system construction} |
87 |
|
88 |
The construction of the pyramidal and secondary prism systems follows that of |
89 |
the basal and prismatic systems presented elsewhere\cite{Louden13}, however |
90 |
the ice crystals and water boxes were equilibrated and combined at 50K |
91 |
instead of 225K. The ice / water systems generated were then equilibrated |
92 |
to 225K. The resulting pyramidal system was |
93 |
$37.47 \times 29.50 \times 93.02$ \AA\ with 1216 |
94 |
SPC/E molecules in the ice slab, and 2203 in the liquid phase. The secondary |
95 |
prism system generated was $71.87 \times 31.66 \times 161.55$ \AA\ with 3840 |
96 |
SPC/E molecules in the ice slab and 8176 molecules in the liquid phase. |
97 |
|
98 |
\subsection{Computational details} |
99 |
% Do we need to justify the sims at 225K? |
100 |
% No crystal growth or shrinkage over 2 successive 1 ns NVT simulations for |
101 |
% either the pyramidal or sec. prism ice/water systems. |
102 |
|
103 |
The computational details performed here were equivalent to those reported |
104 |
in the previous publication\cite{Louden13}. The only changes made to the |
105 |
previously reported procedure were the following. VSS-RNEMD moves were |
106 |
attempted every 2 fs instead of every 50 fs. This was done to minimize |
107 |
the magnitude of each individual VSS-RNEMD perturbation to the system. |
108 |
|
109 |
All pyramidal simulations were performed under the NVT ensamble except those |
110 |
during which statistics were accumulated for the orientational correlation |
111 |
function, which were performed under the NVE ensamble. All secondary prism |
112 |
simulations were performed under the NVE ensamble. |
113 |
|
114 |
\section{Results and discussion} |
115 |
\subsection{Interfacial width} |
116 |
In the literature there is good agreement that between the solid ice and |
117 |
the bulk water, there exists a region of 'slush-like' water molecules. |
118 |
In this region, the water molecules are structurely distinguishable and |
119 |
behave differently than those of the solid ice or the bulk water. |
120 |
The characteristics of this region have been defined by both structural |
121 |
and dynamic properties; and its width has been measured by the change of these |
122 |
properties from their bulk liquid values to those of the solid ice. |
123 |
Examples of these properties include the density, the diffusion constant, and |
124 |
the translational order profile. \cite{Bryk02,Karim90,Gay02,Hayward01,Hayward02,Karim88} |
125 |
|
126 |
Since the VSS-RNEMD moves used to impose the thermal and velocity gradients |
127 |
perturb the momenta of the water molecules in |
128 |
the systems, parameters that depend on translational motion may give |
129 |
faulty results. A stuructural parameter will be less effected by the |
130 |
VSS-RNEMD perturbations to the system. Due to this, we have used the |
131 |
local order tetrahedral parameter to quantify the width of the interface, |
132 |
which was originally described by Kumar\cite{Kumar09} and |
133 |
Errington\cite{Errington01} and explained in our |
134 |
previous publication\cite{Louden13} in relation to an ice/water system. |
135 |
|
136 |
Paragraph and eq. for tetrahedrality here. |
137 |
|
138 |
To determine the width of the interfaces, each of the systems were |
139 |
divided into 100 artificial bins along the |
140 |
$z$-dimension, and the local tetrahedral order parameter, $q(z)$, was |
141 |
time-averaged for each of the bins, resulting in a tetrahedrality profile of |
142 |
the system. These profiles are shown across the $z$-dimension of the systems |
143 |
in panel $a$ of Figures \ref{fig:spComic} |
144 |
and \ref{fig:pyrComic} (black circles). The $q(z)$ function has a range of |
145 |
(0,1), where a larger value indicates a more tetrahedral environment. |
146 |
The $q(z)$ for the bulk liquid was found to be $\approx $ 0.77, while values of |
147 |
$\approx $0.92 were more common for the ice. The tetrahedrality profiles were |
148 |
fit using a hyperbolic tangent\cite{Louden13} designed to smoothly fit the |
149 |
bulk to ice |
150 |
transition, while accounting for the thermal influence on the profile by the |
151 |
kinetic energy exchanges of the VSS-RNEMD moves. In panels $b$ and $c$, the |
152 |
imposed thermal and velocity gradients can be seen. The verticle dotted |
153 |
lines traversing all three panels indicate the midpoints of the interface |
154 |
as determined by the hyperbolic tangent fit of the tetrahedrality profiles. |
155 |
|
156 |
From fitting the tetrahedrality profiles for each of the 0.5 nanosecond |
157 |
simulations (panel c of Figures \ref{fig:spComic} and \ref{fig:pyrComic}) |
158 |
by Eq. 6\cite{Louden13},we find the interfacial width to be |
159 |
$3.2 \pm 0.2$ and $3.2 \pm 0.2$ \AA\ for the control system with no applied |
160 |
momentum flux for both the pyramidal and secondary prism systems. |
161 |
Over the range of shear rates investigated, |
162 |
$0.6 \pm 0.2 \mathrm{ms}^{-1} \rightarrow 5.6 \pm 0.4 \mathrm{ms}^{-1}$ for |
163 |
the pyramidal system and $0.9 \pm 0.3 \mathrm{ms}^{-1} \rightarrow 5.4 \pm 0.1 |
164 |
\mathrm{ms}^{-1}$ for the secondary prism, we found no significant change in |
165 |
the interfacial width. This follows our previous findings of the basal and |
166 |
prismatic systems, in which the interfacial width was invarient of the |
167 |
shear rate of the ice. The interfacial width of the quiescent basal and |
168 |
prismatic systems was found to be $3.2 \pm 0.4$ \AA\ and $3.6 \pm 0.2$ \AA\ |
169 |
respectively. Over the range of shear rates investigated, $0.6 \pm 0.3 |
170 |
\mathrm{ms}^{-1} \rightarrow 5.3 \pm 0.5 \mathrm{ms}^{-1}$ for the basal |
171 |
system and $0.9 \pm 0.2 \mathrm{ms}^{-1} \rightarrow 4.5 \pm 0.1 |
172 |
\mathrm{ms}^{-1}$ for the prismatic. |
173 |
|
174 |
These results indicate that the surface structure of the exposed ice crystal |
175 |
has little to no effect on how far into the bulk the ice-like structural |
176 |
ordering is. Also, it appears that the interface is not structurally effected |
177 |
by shearing the ice through water. |
178 |
|
179 |
|
180 |
\subsection{Orientational dynamics} |
181 |
%Should we include the math here? |
182 |
The orientational time correlation function, |
183 |
\begin{equation}\label{C(t)1} |
184 |
C_{2}(t)=\langle P_{2}(\mathbf{u}(0)\cdot \mathbf{u}(t))\rangle, |
185 |
\end{equation} |
186 |
helps indicate the local environment around the water molecules. The function |
187 |
begins with an initial value of unity, and decays to zero as the water molecule |
188 |
loses memory of its former orientation. Observing the rate at which this decay |
189 |
occurs can provide insight to the mechanism and timescales for the relaxation. |
190 |
In eq. \eqref{C(t)1}, $P_{2}$ is the second-order Legendre polynomial, and |
191 |
$\mathbf{u}$ is the the bisecting HOH vector. The angle brackets indicate |
192 |
an ensemble average over all the water molecules in a given spatial region. |
193 |
|
194 |
To investigate the dynamics of the water molecules across the interface, the |
195 |
systems were divided in the $z$-dimension into bins, each $\approx$ 3 \AA\ |
196 |
wide, and \eqref{C(t)1} was computed for each of the bins. A water |
197 |
molecule was allocated to a particular bin if it was initially in the bin |
198 |
at time zero. To compute \eqref{C(t)1}, each 0.5 ns simulation was followed |
199 |
by an additional 200 ps microcanonical (NVE) simulation during which the |
200 |
position and orientations of each molecule were recorded every 0.1 ps. |
201 |
|
202 |
The data obtained for each bin was then fit to a triexponential decay given by |
203 |
\begin{equation}\label{C(t)_fit} |
204 |
C_{2}(t) \approx a e^{-t/\tau_\mathrm{short}} + b e^{-t/\tau_\mathrm{middle}} +\ |
205 |
c |
206 |
e^{-t/\tau_\mathrm{long}} + (1-a-b-c) |
207 |
\end{equation} |
208 |
where $\tau_{short}$ corresponds to the librational motion of the water |
209 |
molecules, $\tau_{middle}$ corresponds to jumps between the breaking and |
210 |
making of hydrogen bonds, and $\tau_{long}$ corresponds to the translational |
211 |
motion of the water molecules. The last term in \eqref{C(t)_fit} accounts |
212 |
for the water molecules trapped in the ice which do not experience any |
213 |
long-time orientational decay. |
214 |
|
215 |
In Figures \ref{fig:PyrOrient} and \ref{fig:SPorient} we see the $z$-coordinate |
216 |
profiles for the three decay constants, $\tau_{short}$ (panel a), |
217 |
$\tau_{middle}$ (panel b), |
218 |
and $\tau_{long}$ (panel c) for the pyramidal and secondary prismatic systems |
219 |
respectively. The control experiments (no shear) are shown in black, and |
220 |
an experiment with an imposed momentum flux is shown in red. The vertical |
221 |
dotted line traversing all three panels denotes the midpoint of the |
222 |
interface as determined by the local tetrahedral order parameter fitting. |
223 |
In the liquid regions of both systems, we see that $\tau_{middle}$ and |
224 |
$\tau_{long}$ have approximately consistent values of $3-6$ ps and $30-40$ ps, |
225 |
resepctively, and increase in value as we approach the interface. Conversely, |
226 |
in panel a, we see that $\tau_{short}$ decreases from the liquid value |
227 |
of $72-76$ fs as we approach the interface. We believe this speed up is due to |
228 |
the constrained motion of librations closer to the interface. Both the |
229 |
approximate values for the decays and relative trends match those reported |
230 |
previously for the basal and prismatic interfaces. |
231 |
|
232 |
As done previously, we have attempted to quantify the distance, $d_{pyramidal}$ |
233 |
and $d_{secondary prism}$, from the |
234 |
interface that the deviations from the bulk liquid values begin. This was done |
235 |
by fitting the orientational decay constant $z$-profiles by |
236 |
\begin{equation}\label{tauFit} |
237 |
\tau(z)\approx\tau_{liquid}+(\tau_{solid}-\tau_{liquid})e^{-(z-z_{wall})/d} |
238 |
\end{equation} |
239 |
where $\tau_{liquid}$ and $\tau_{solid}$ are the liquid and projected solid |
240 |
values of the decay constants, $z_{wall}$ is the location of the interface, |
241 |
and $d$ is the displacement from the interface at which these deviations |
242 |
occur. The values for $d_{pyramidal}$ and $d_{secondary prismatic}$ were |
243 |
determined |
244 |
for each of the decay constants, and then averaged for better statistics |
245 |
($\tau_{middle}$ was ommitted for secondary prism). For the pyramidal system, |
246 |
$d_{pyramidal}$ was found to be 2.7 \AA\ for both the control and the sheared |
247 |
system. We found $d_{secondary prismatic}$ to be slightly larger than |
248 |
$d_{pyramidal}$ for both the control and with an applied shear, with |
249 |
displacements of $4$ \AA\ for the control system and $3$ \AA\ for the |
250 |
experiment with the imposed momentum flux. These values are consistent with |
251 |
those found for the basal ($d_{basal}\approx2.9$ \AA\ ) and prismatic |
252 |
($d_{prismatic}\approx3.5$ \AA\ ) systems. |
253 |
|
254 |
\subsection{Coefficient of friction of the interfaces} |
255 |
While investigating the kinetic coefficient of friction for the larger |
256 |
prismatic system, there was found to be a dependence for $\mu_k$ |
257 |
on the temperature of the liquid water in the system. We believe this |
258 |
dependence |
259 |
arrises from the sharp discontinuity of the viscosity for the SPC/E model |
260 |
at temperatures approaching 200 K\cite{kuang12}. Due to this, we propose |
261 |
a weighting to the structural interfacial parameter, $\kappa$ by the |
262 |
viscosity at $225$ K, the temperature of the interface. $\kappa$ is |
263 |
traditionally defined as |
264 |
\begin{equation}\label{kappa} |
265 |
\kappa = \eta/\delta |
266 |
\end{equation} |
267 |
where $\eta$ is the viscosity and $\delta$ is the slip length. |
268 |
In our ice/water shearing simulations, the system has reached a steady state |
269 |
when the applied force, |
270 |
|
271 |
\begin{equation} |
272 |
f_{applied} = \mathbf{j}_z(\mathbf{p})L_x L_y |
273 |
\end{equation} |
274 |
is equal to the frictional force resisting the motion of the ice block |
275 |
\begin{equation} |
276 |
f_{friction} = \frac{\eta \mathbf{v} L_x L_y}{\delta} |
277 |
\end{equation} |
278 |
where $\mathbf{v}$ is the relative velocity of the liquid from the ice. |
279 |
When this condition is met, we are able to solve the resulting expression to |
280 |
obtain, |
281 |
\begin{equation}\label{force_equality} |
282 |
\frac{\eta}{\delta} = \frac{\mathbf{j}_z(\mathbf{p})}{\mathbf{v}} |
283 |
\end{equation} |
284 |
From \eqref{kappa}, \eqref{force_equality} becomes |
285 |
\begin{equation} |
286 |
\kappa = \frac{\mathbf{j}_z(\mathbf{p})}{\mathbf{v}} |
287 |
\end{equation} |
288 |
which we will multiply by a viscosity weighting term to reach |
289 |
\begin{equation} \label{kappa2} |
290 |
\kappa = \frac{\mathbf{j}_z(\mathbf{p})}{\mathbf{v}} \frac{\eta(225)}{\eta(T)} |
291 |
\end{equation} |
292 |
Assuming linear response theory is valid, an expression for ($\eta$) can |
293 |
be found from the imposed momentum flux and the measured velocity gradient. |
294 |
\begin{equation}\label{eta_eq} |
295 |
\eta = \frac{\mathbf{j}_z(\mathbf{p})}{\frac{\partial v_x}{\partial z}} |
296 |
\end{equation} |
297 |
Substituting eq \eqref{eta_eq} into eq \eqref{kappa2} we arrive at |
298 |
\begin{equation} |
299 |
\kappa = \frac{\frac{\partial v_x}{\partial z}}{\mathbf{v}}\eta(225) |
300 |
\end{equation} |
301 |
|
302 |
\begin{table}[h] |
303 |
\centering |
304 |
\caption{$\kappa$ values for the basal, prismatic, pyramidal, and secondary prismatic facets of Ice-I$_\mathrm{h}$} |
305 |
\label{tab:kappa} |
306 |
\begin{tabular}{|ccc|} \hline |
307 |
& \multicolumn{2}{c|}{$\kappa_{Drag direction}$} \\ |
308 |
Interface & $\kappa_{x}$ & $\kappa_{y}$ \\ \hline |
309 |
basal & $0.00059 \pm 0.00003$ & $0.00065 \pm 0.00008$ \\ |
310 |
prismatic & $0.00030 \pm 0.00002$ & $0.00030 \pm 0.00001$ \\ |
311 |
pyramidal & $0.00058 \pm 0.00004$ & $0.00061 \pm 0.00005$ \\ |
312 |
secondary prism & $0.00035 \pm 0.00001$ & $0.00033 \pm 0.00002$ \\ \hline |
313 |
\end{tabular} |
314 |
\end{table} |
315 |
|
316 |
|
317 |
To obtain the value of $\eta(225)$ for the SPC/E model, a $31.09 \times 29.38 |
318 |
\times 124.39$ \AA\ box with 3744 water molecules was equilibrated to 225K, |
319 |
and 5 unique shearing experiments were performed. Each experiment was |
320 |
conducted in the microcanonical ensemble (NVE) and were 5 ns in |
321 |
length. The VSS were attempted every timestep, which was set to 2 fs. |
322 |
For our SPC/E systems, we found $\eta(225)$ to be $0.0148 \pm 0.0007 Pa s$, |
323 |
roughly ten times larger than the value found for 280 K SPC/E water by |
324 |
Kuang\cite{kuang12}. |
325 |
|
326 |
|
327 |
\begin{table}[h] |
328 |
\centering |
329 |
\caption{Solid-liquid friction coefficients (measured in amu~fs\textsuperscript\ |
330 |
{-1}). \\ |
331 |
\textsuperscript{a} See ref. \onlinecite{Louden13}. } |
332 |
\label{tab:lambda} |
333 |
\begin{tabular}{|ccc|} \hline |
334 |
& \multicolumn{2}{c|}{Drag direction} \\ |
335 |
Interface & $x$ & $y$ \\ \hline |
336 |
basal\textsuperscript{a} & $0.08 \pm 0.02$ & $0.09 \pm 0.03$ \\ |
337 |
prismatic (T = 225)\textsuperscript{a} & $0.037 \pm 0.008$ & $0.04 \pm 0.01$ \\ |
338 |
prismatic (T = 230) & $0.10 \pm 0.01$ & $0.070 \pm 0.006$\\ |
339 |
pyramidal & $0.13 \pm 0.03$ & $0.14 \pm 0.03$ \\ |
340 |
secondary prism & $0.13 \pm 0.02$ & $0.12 \pm 0.03$ \\ \hline |
341 |
\end{tabular} |
342 |
\end{table} |
343 |
|
344 |
|
345 |
\begin{figure} |
346 |
\includegraphics[width=\linewidth]{Pyr-orient} |
347 |
\caption{\label{fig:PyrOrient} The three decay constants of the |
348 |
orientational time correlation function, $C_2(t)$, for water as a function |
349 |
of distance from the center of the ice slab. The vertical dashed line |
350 |
indicates the edge of the pyramidal ice slab determined by the local order |
351 |
tetrahedral parameter. The control (black circles) and sheared (red squares) |
352 |
experiments were fit by a shifted exponential decay (Eq. 9\cite{Louden13}) |
353 |
shown by the black and red lines respectively. The upper two panels show that |
354 |
translational and hydrogen bond making and breaking events slow down |
355 |
through the interface while approaching the ice slab. The bottom most panel |
356 |
shows the librational motion of the water molecules speeding up approaching |
357 |
the ice block due to the confined region of space allowed for the molecules |
358 |
to move in.} |
359 |
\end{figure} |
360 |
|
361 |
\begin{figure} |
362 |
\includegraphics[width=\linewidth]{SP-orient-less} |
363 |
\caption{\label{fig:SPorient} Decay constants for $C_2(t)$ at the secondary |
364 |
prism face. Panel descriptions match those in \ref{fig:PyrOrient}.} |
365 |
\end{figure} |
366 |
|
367 |
|
368 |
|
369 |
\section{Conclusion} |
370 |
Conclude conclude conclude... |
371 |
|
372 |
|
373 |
\begin{acknowledgments} |
374 |
Support for this project was provided by the National |
375 |
Science Foundation under grant CHE-1362211. Computational time was |
376 |
provided by the Center for Research Computing (CRC) at the |
377 |
University of Notre Dame. |
378 |
\end{acknowledgments} |
379 |
|
380 |
\newpage |
381 |
|
382 |
\bibliography{iceWater} |
383 |
|
384 |
\end{document} |