6,141 research outputs found
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
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
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
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
Elastohydrodynamics for soft solids with surface roughness: transient effects
A huge number of technological and biological systems involves the lubricated
contact between rough surfaces of soft solids in relative accelerated motion.
Examples include dynamical rubber seals and the human joints. In this study we
consider an elastic cylinder with random surface roughness in accelerated
sliding motion on a rigid, perfectly flat (no roughness) substrate in a fluid.
We calculate the surface deformations, interface separation and the
contributions to the friction force and the normal force from the area of real
contact and from the fluid. The driving velocity profile as a function of time
is assumed to be either a sine-function, or a linear multi-ramp function. We
show how the squeeze-in and squeeze-out processes, occurring in accelerated
sliding, quantitatively affect the Stribeck curve with respect to the steady
sliding. Finally, the theory results are compared to experimental data
Quantum-dot thermometry
We present a method for the measurement of a temperature differential across
a single quantum dot that has transmission resonances that are separated in
energy by much more than the thermal energy. We determine numerically that the
method is accurate to within a few percent across a wide range of parameters.
The proposed method measures the temperature of the electrons that enter the
quantum dot and will be useful in experiments that aim to test theory which
predicts quantum dots are highly-efficient thermoelectrics.Comment: 3 pages, 4 Figure
Velocity weakening and possibility of aftershocks in nanofriction experiments
We study the frictional behavior of small contacts as those realized in the
atomic force microscope and other experimental setups, in the framework of
generalized Prandtl-Tomlinson models. Particular attention is paid to
mechanisms that generate velocity weakening, namely a decreasing average
friction force with the relative sliding velocity.The mechanisms studied model
the possibility of viscous relaxation, or aging effects in the contact. It is
found that, in addition to producing velocity weakening, these mechanisms can
also produce aftershocks at sufficiently low sliding velocities. This provides
a remarkable analogy at the microscale, of friction properties at the
macroscale, where aftershocks and velocity weakening are two fundamental
features of seismic phenomena.Comment: 8 pages, 7 figure
- …