2 research outputs found
Orders of Magnitude Changes in the Friction of an Ionic Liquid on Carbonaceous Surfaces
The
fast development of ionic liquids as new lubricants and carbon-based
coatings as performant tribological surfaces calls for the characterization
of their frictional and interfacial hydrodynamic behavior. Here we
use molecular dynamics simulations to explore the response under shear
of an ionic liquid confined between various carbon-based surfaces
and an iron oxide surface for comparison. We show that extremely low
fluid friction and giant hydrodynamic slippage can be obtained on
graphite and to a lesser extent on diamond, but that friction on amorphous
carbon surfaces is comparable to that on iron oxide. We relate these
differences to the atom-scale roughness of the surfaces. In particular,
although amorphous carbon surfaces are apolar, their nanometric roughness
is enough to generate a fluid friction comparable to that of the extremely
smooth but polar iron oxide surface. We also show that, at high shear
rates, seemingly small differences in viscosity and interfacial friction
can result in a significant change of the slip length. We finally
discuss the consequences of the ultralow fluid friction that we observed
on the macroscopic behavior of lubricated contacts
Mixed Mechanism of Lubrication by Lipid Bilayer Stacks
Although the key role of lipid bilayer
stacks in biological lubrication
is generally accepted, the mechanisms underlying their extreme efficiency
remain elusive. In this article, we report molecular dynamics simulations
of lipid bilayer stacks undergoing load and shear. When the hydration
level is reduced, the velocity accommodation mechanism changes from
viscous shear in hydration water to interlayer sliding in the bilayers.
This enables stacks of hydrated lipid bilayers to act as efficient
boundary lubricants for various hydration conditions, structures,
and mechanical loads. We also propose an estimation for the friction
coefficient; thanks to the strong hydration forces between lipid bilayers,
the high local viscosity is not in contradiction with low friction
coefficients