10,614 research outputs found
Contact mechanics with adhesion: Interfacial separation and contact area
We study the adhesive contact between elastic solids with randomly rough,
self affine fractal surfaces. We present molecular dynamics (MD) simulation
results for the interfacial stress distribution and the wall-wall separation.
We compare the MD results for the relative contact area and the average
interfacial separation, with the prediction of the contact mechanics theory of
Persson. We find good agreement between theory and the simulation results. We
apply the theory to the system studied by Benz et al. involving polymer in
contact with polymer, but in this case the adhesion gives only a small
modification of the interfacial separation as a function of the squeezing
pressure.Comment: 5 pages, 4 figure
Leak-rate of seals: comparison of theory with experiment
Seals are extremely useful devices to prevent fluid leakage. We present
experimental results for the leak-rate of rubber seals, and compare the results
to a novel theory, which is based on percolation theory and a recently
developed contact mechanics theory. We find good agreement between theory and
experiment.Comment: 6 pages, 10 figure
Collective Sliding States for Colloidal Molecular Crystals
We study the driving of colloidal molecular crystals over periodic substrates
such as those created with optical traps. The n-merization that occurs in the
colloidal molecular crystal states produces a remarkably rich variety of
distinct dynamical behaviors, including polarization effects within the pinned
phase and the formation of both ordered and disordered sliding phases. Using
computer simulations, we map the dynamic phase diagrams as a function of
substrate strength for dimers and trimers on a triangular substrate, and
correlate features on the phase diagram with transport signatures.Comment: 4 pages, 5 postscript figure
Pinning and Dynamics of Colloids on One Dimensional Periodic Potentials
Using numerical simulations we study the pinning and dynamics of interacting
colloids on periodic one-dimensional substrates. As a function of colloid
density, temperature, and substrate strength, we find a variety of pinned and
dynamic states including pinned smectic, pinned buckled, two-phase flow, and
moving partially ordered structures. We show that for increasing colloid
density, peaks in the depinning threshold occur at commensurate states. The
scaling of the pinning threshold versus substrate strength changes when the
colloids undergo a transition from one-dimensional chains to a buckled
configuration.Comment: 4 pages, 4 postscript figure
Interfacial separation between elastic solids with randomly rough surfaces: comparison of experiment with theory
We study the average separation between an elastic solid and a hard solid
with a nominal flat but randomly rough surface, as a function of the squeezing
pressure. We present experimental results for a silicon rubber (PDMS) block
with a flat surface squeezed against an asphalt road surface. The theory shows
that an effective repulse pressure act between the surfaces of the form p
proportional to exp(-u/u0), where u is the average separation between the
surfaces and u0 a constant of order the root-mean-square roughness, in good
agreement with the experimental results.Comment: 6 pages, 10 figure
Rubber friction on (apparently) smooth lubricated surfaces
We study rubber sliding friction on hard lubricated surfaces. We show that
even if the hard surface appears smooth to the naked eye, it may exhibit short
wavelength roughness, which may give the dominant contribution to rubber
friction. That is, the observed sliding friction is mainly due to the
viscoelastic deformations of the rubber by the substrate surface asperities.
The presented results are of great importance for rubber sealing and other
rubber applications involving (apparently) smooth surfaces.Comment: 7 pages, 15 figure
Local Melting and Drag for a Particle Driven Through a Colloidal Crystal
We numerically investigate a colloidal particle driven through a colloidal
crystal as a function of temperature. When the charge of the driven particle is
larger or comparable to that of the colloids comprising the crystal, a local
melting can occur, characterized by defect generation in the lattice
surrounding the driven particle. The generation of the defects is accompanied
by an increase in the drag force on the driven particle, as well as large noise
fluctuations. We discuss the similarities of these results to the peak effect
phenomena observed for vortices in superconductors.Comment: 4 pages, 4 postscript figure
How do liquids confined at the nanoscale influence adhesion?
Liquids play an important role in adhesion and sliding friction. They behave
as lubricants in human bodies especially in the joints. However, in many
biological attachment systems they acts like adhesives, e.g. facilitating
insects to move on ceilings or vertical walls. Here we use molecular dynamics
to study how liquids confined at the nanoscale influence the adhesion between
solid bodies with smooth and rough surfaces. We show that a monolayer of liquid
may strongly affect the adhesion.Comment: 5 pages, 9 color figures. Some figures are in Postscript Level 3
format. Minimal changes with respect to the previous version. Added doi and
reference to the published article also inside the pape
On the dependence of the leak-rate of seals on the skewness of the surface height probability distribution
Seals are extremely useful devices to prevent fluid leakage. We present
experimental result which show that the leak-rate of seals depend sensitively
on the skewness in the height probability distribution. The experimental data
are analyzed using the critical-junction theory. We show that using the
top-power spectrum result in good agreement between theory and experiment.Comment: 5 pages, 9 figure
Nanodroplets on rough hydrophilic and hydrophobic surfaces
We present results of Molecular Dynamics (MD) calculations on the behavior of
liquid nanodroplets on rough hydrophobic and hydrophilic solid surfaces. On
hydrophobic surfaces, the contact angle for nanodroplets depends strongly on
the root mean square roughness amplitude, but it is nearly independent of the
fractal dimension of the surface. Since increasing the fractal dimension
increases the short-wavelength roughness, while the long-wavelength roughness
is almost unchanged, we conclude that for hydrophobic interactions the
short-wavelength (atomistic) roughness is not very important. We show that the
nanodroplet is in a Cassie-like state. For rough hydrophobic surfaces, there is
no contact angle hysteresis due to strong thermal fluctuations, which occur at
the liquid-solid interface on the nanoscale. On hydrophilic surfaces, however,
there is strong contact angle hysteresis due to higher energy barrier. These
findings may be very important for the development of artificially biomimetic
superhydrophobic surfaces.Comment: 15 pages, 25 figures. Minimal changes with respect to the previous
one. A few small improvements, references updated, added the reference to the
published paper. Previous work on the same subject: arXiv:cond-mat/060405
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