8,604 research outputs found
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
Fluid flow at the interface between elastic solids with randomly rough surfaces
I study fluid flow at the interface between elastic solids with randomly
rough surfaces. I use the contact mechanics model of Persson to take into
account the elastic interaction between the solid walls and the Bruggeman
effective medium theory to account for the influence of the disorder on the
fluid flow. I calculate the flow tensor which determines the pressure flow
factor and, e.g., the leak-rate of static seals. I show how the perturbation
treatment of Tripp can be extended to arbitrary order in the ratio between the
root-mean-square roughness amplitude and the average interfacial surface
separation. I introduce a matrix D(Zeta), determined by the surface roughness
power spectrum, which can be used to describe the anisotropy of the surface at
any magnification Zeta. I present results for the asymmetry factor Gamma(Zeta)
(generalized Peklenik number) for grinded steel and sandblasted PMMA surfaces.Comment: 16 pages, 14 figure
Electronic friction and liquid-flow-induced voltage in nanotubes
A recent exciting experiment by Ghosh et al. reported that the flow of an
ion-containing liquid such as water through bundles of single-walled carbon
nanotubes induces a voltage in the nanotubes that grows logarithmically with
the flow velocity v0. We propose an explanation for this observation. Assuming
that the liquid molecules nearest the nanotube form a 2D solid-like monolayer
pinned through the adsorbed ions to the nanotubes, the monolayer sliding will
occur by elastic loading followed by local yield (stick-slip). The drifting
adsorbed ions produce a voltage in the nanotube through electronic friction
against free electrons inside the nanotube. Thermally excited jumps over
force-biased barriers, well-known in stick-slip, can explain the logarithmic
voltage growth with flow velocity. We estimate the short circuit current and
the internal resistance of the nanotube voltage generator.Comment: 8 pages, 3 figures; published on PRB
(http://link.aps.org/abstract/PRB/v69/e235410) and on the Virtual Journal of
Nanoscale Science and Technology (http://www.vjnano.org, July 14, 2002, Vol.
10, Iss. 2
Dynamical transitions and sliding friction in the two-dimensional Frenkel-Kontorova model
The nonlinear response of an adsorbed layer on a periodic substrate to an
external force is studied via a two dimensional uniaxial Frenkel-Kontorova
model. The nonequlibrium properties of the model are simulated by Brownian
molecular dynamics. Dynamical phase transitions between pinned solid, sliding
commensurate and incommensurate solids and hysteresis effects are found that
are qualitatively similar to the results for a Lennard-Jones model, thus
demonstrating the universal nature of these features.Comment: 11 pages, 12 figures, to appear in Phys. Rev.
Transverse thermal depinning and nonlinear sliding friction of an adsorbed monolayer
We study the response of an adsorbed monolayer under a driving force as a
model of sliding friction phenomena between two crystalline surfaces with a
boundary lubrication layer. Using Langevin-dynamics simulation, we determine
the nonlinear response in the direction transverse to a high symmetry direction
along which the layer is already sliding. We find that below a finite
transition temperature, there exist a critical depinning force and hysteresis
effects in the transverse response in the dynamical state when the adlayer is
sliding smoothly along the longitudinal direction.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Enhancement of noncontact friction between closely spaced bodies by two-dimensional systems
. We consider the effect of an external bias voltage and the spatial
variation of the surface potential, on the damping of cantilever vibrations.
The electrostatic friction is due to energy losses in the sample created by the
electromagnetic field from the oscillating charges induced on the surface of
the tip by the bias voltage and spatial variation of the surface potential. A
similar effect arises when the tip is oscillating in the electrostatic field
created by charged defects in a dielectric substrate. The electrostatic
friction is compared with the van der Waals friction originating from the
fluctuating electromagnetic field due to quantum and thermal fluctuation of the
current density inside the bodies. We show that the electrostatic and van der
Waals friction can be greatly enhanced if on the surfaces of the sample and the
tip there are two-dimension (2D) systems, e.g. a 2D-electron system or
incommensurate layers of adsorbed ions exhibiting acoustic vibrations. We show
that the damping of the cantilever vibrations due to the electrostatic friction
may be of similar magnitude as the damping observed in recent experiments of
Stipe \textit{et al} [B.C.Stipe, H.J.Mamin, T.D.Stowe, T.W.Kenny, and D.Rugar,
Phys.Rev. Lett.% \textbf{87}, 0982001]. We also show that at short separation
the van der Waals friction may be large enough to be measured experimentally.Comment: 11 pages, 2 figure
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