1
Bounded Amplification of Diffusioosmosis utilizing Hydrophobicity
Vahid Hoshyargar
a
, Arman Sadeghi
b
, and Seyed Nezameddin Ashrafizadeh
a,1
a
Research Lab for Advanced Separation Processes, Department of Chemical Engineering,
Iran University of Science and Technology, Narmak, Tehran 16846-13114, Iran
b
Department of Mechanical Engineering, University of Kurdistan, Sanandaj 66177-15175, Iran
Supporting Information
The molecular dynamic (MD) is a realistic powerful computational technique for simulating the real behavior of systems
only by solving the simple equation of motion of limited particles. The physical properties of materials can also be
predicted if an interacting potential between particles are deemed. The so-called “time integration” reveals the trajectory
and physical movements of atoms, molecules, and ions in the system. The atoms are interacting with each other and almost
all properties (e.g. pressure, temperature, energy, etc) are affected by. One can claim that assuming a proper potential
between particles definitely guarantees a good prediction. No limiting assumption in MD makes it an accurate tool to study
the properties of systems
1, 2
. In this supporting information, we are summarizing the whole parameters needed to perform
molecular dynamics (MD) simulation of DOF by using LAMMPS package (version 2015)
3
and thereafter the method we
can obtain the slip length to feed to continuum hydrodynamics from the MD results.
S1. Unit cell structure
A unit cell is constructed by confining the electrolyte in between two parallel walls (See Fig. S1). Each wall consists of
multiple duplicates of a closed-packed Face-Centered Cubic (FCC) crystal by in lattice size (
). The FCC lattice
is extended in and directions; respectively, 9, 6, and 3 times for each wall. The walls are separated by ~9 lattice
spacing times while the exact distance between the walls is determined when the total normal component of stress
tensor per unit volume of electrolyte is in average. In order to constitute an electrolyte, atoms are dispersed in
water molecules to produce a concentration of about . The SPC/E model is used in the simulation of the water
molecules to closely follow the properties of the aqueous solution. Corresponding numbers of water and ions relative to the
electrolyte concentration are defined by setting the fluid density equal to
. The layer of each wall which is in
contact with the fluid is carrying a fixed charge corresponding to the electric charge density of the wall,
. An
important note in this respect is keeping the electroneutrality of the whole system by reducing the charge of coions and
increasing the charge of counterion at the same time which sums up an equivalent charge to the prescribed charge of both
the walls. To model a slit geometry, periodic boundary conditions are applied only in and directions.
S2. Forcefield
The forcefield is established by short-ranged interactions between particles utilizing the Lennard-Jones (LJ) 6-12 force,
(
)
(
)
(
)
, added to a long-ranged electrostatic Coulomb force, calculated by
method, bearing in mind that dipole interactions should be removed since the system is not periodic in direction. LJ
parameters of homonuclear are listed in Table S1 while those of heteronuclears are calculated via geometric and
arithmetic average, respectively for
and
(Lorentz-Berthelot rule).
1
Corresponding author
E-mail addresses: hoshyargar@iust.ac.ir (V. Hoshyargar) , a.sadeghi@eng.uok.ac.ir (A. Sadeghi), ashrafi@iust.ac.ir (S.N. Ashrafizadeh)
Electronic Supplementary Material (ESI) for RSC Advances.
This journal is © The Royal Society of Chemistry 2016