167 research outputs found
Structure and Diffusion of Nanoparticle Monolayers Floating at Liquid/Vapor Interfaces: A Molecular Dynamics Study
Large-scale molecular dynamics simulations are used to simulate a layer of
nanoparticles diffusing on the surface of a liquid. Both a low viscosity
liquid, represented by Lennard-Jones monomers, and a high viscosity liquid,
represented by linear homopolymers, are studied. The organization and diffusion
of the nanoparticles are analyzed as the nanoparticle density and the contact
angle between the nanoparticles and liquid are varied. When the interaction
between the nanoparticles and liquid is reduced the contact angle increases and
the nanoparticles ride higher on the liquid surface, which enables them to
diffuse faster. In this case the short range order is also reduced as seen in
the pair correlation function. For the polymeric liquids, the out-of-layer
fluctuation is suppressed and the short range order is slightly enhanced.
However, the diffusion becomes much slower and the mean square displacement
even shows sub-linear time dependence at large times. The relation between
diffusion coefficient and viscosity is found to deviate from that in bulk
diffusion. Results are compared to simulations of the identical nanoparticles
in 2-dimensions.Comment: 8 pages, 9 figure
Effect of Particle Shape and Charge on Bulk Rheology of Nanoparticle Suspensions
The rheology of nanoparticle suspensions for nanoparticles of various shapes
with equal mass is studied using molecular dynamics simulations. The
equilibrium structure and the response to imposed shear are analyzed for
suspensions of spheres, rods, plates, and jacks in an explicit solvent for both
charged and uncharged nanoparticles. For the volume fraction studied,
?, the uncharged systems are all in their isotropic phase and
the viscosity is only weakly dependent on shape for spheres, rods, and plate
whereas for the jacks the viscosity is an order of magnitude larger than for
the other three shapes. The introduction of charge increases the viscosity for
all four nanoparticle shapes with the increase being the largest for rods and
plates. The presence of a repulsive charge between the particles decreases the
amount of stress reduction that can be achieved by particle reorientation.Comment: 15 pages, 9 figures, in pres
Capillary waves at the liquid-vapor interface and the surface tension of water models
Capillary waves occurring at the liquid-vapor interface of water are studied
using molecular dynamics simulations. In addition, the surface tension,
determined thermodynamically from the difference in the normal and tangential
pressure at the liquid-vapor interface, is compared for a number of standard
three- and four-point water models. We study four three-point models (SPC/E,
TIP3P, TIP3P-CHARMM, and TIP3P-Ew) and two four-point models (TIP4P and
TIP4P-Ew). All of the models examined underestimate the surface tension; the
TIP4P-Ew model comes closest to reproducing the experimental data. The surface
tension can also be determined from the amplitude of capillary waves at the
liquid-vapor interface by varying the surface area of the interface. The
surface tensions determined from the amplitude of the logarithmic divergence of
the capillary interfacial width and from the traditional thermodynamic method
agree only if the density profile is fitted to an error function instead of a
hyperbolic tangent function.Comment: 11 pages, 8 figures, 7 tables. Accepted for publication in J. Chem.
Phys. [v2: Added references, corrected minor errors
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