136 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 Liquid/Vapor Interfaces: A Molecular Dynamics Simulation
Evidence for capillary waves at a liquid/vapor interface are presented from
extensive molecular dynamics simulations of a system containing up to 1.24
million Lennard-Jones particles. Careful measurements show that the total
interfacial width depends logarithmically on , the length of the
simulation cell parallel to the interface, as predicted theoretically. The
strength of the divergence of the interfacial width on depends
inversely on the surface tension . This allows us to measure
two ways since can also be obtained from the difference in the
pressure parallel and perpendicular to the interface. These two independent
measures of agree provided that the interfacial order parameter
profile is fit to an error function and not a hyperbolic tangent, as often
assumed. We explore why these two common fitting functions give different
results for
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