Friction Force and its Relationship to the Electrostatic Charges at...

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Friction Force and its Relationship to the
Electrostatic Charges at Interfaces
Dr. Thiago A L Burgo

Outline

Unicamp

•  Friction coefficient induced
by electrostatic charges
–  Coefficient of rolling
resistance x El...

Explosions triggered by electrostatic discharge
https://www.youtube.com/watch?
v=6lKUsUycBNA&spfreload=10
www.firesciencet...

In October 2013, a fire of
great proportions hit
Copersucar facilities.

•  For nanotechnology
–  Electrostatic force is even
larger than the inertial
force, for micromachine
parts made of insula...

Challenges
Faced
By
Solar
Energy
Use

Calle et al. Active dust control and mitigation technology for lun...

Electrodynamic
Repulsion

Courtesy of Carlos Calle, Electrostatics and Surface Physics Laboratory - NASA

Surfaces
under
rela<ve
mo<on:

Triboplasma

Heinicke G.
Tribochemistry.
(1984)
Matta et al. J.
Phys. D: App...

How
powerful
is
the
triboplasma?

!
Camara et al. Correlation between nanosecond X-ray
flashes and stick–sl...

What
creates
sta/c
electricity?

Williams, M.W. What creates static electricity? American Scientist 100, 316-3...

Polymer

Ethanol

2
hours

Clean
Polymer

drying

Electrical
poten<al
scanning

with
Kelv...

1 cm
Bipolar Segregated
Domain

Formation free-radicals is followed by electron transfer:
from the hydrocarbon free-radicals to the more
electronegative f...

Francisco, K. R., Burgo, T. A. L., Galembeck, F. Tribocharged
Polymer Surfaces: Solvent Effect on Pattern Formation and
Mo...

Mo<va<on
and
hypothesis

•  Triboeletriﬁca<on:
glass
beads
over

PE
or
PTFE;

•  Fric<on
...

Tribology: science of friction
•  “The
science
and
technology
of
interac<ng
surfaces
in
rela<ve
...

Real
contact
area
and
adhesion

•  Connec<ons
from
micro
to
macro

scale
is
very
di...

Mechanical
contact:

JKR,
DMT
and
Maugis

•  JKR:
Adhesion
forces
change
contact
area
...

…and
the
Coulombic
contribu<on?

“…The primary obstacle to inclusion of sliding
triboelectrification into our ...

Coeﬃcient
of
Rolling
Resistance
(CoRR)
x

Electrosta<c
Poten<al

A"
B" C"h
d
CoRR = h/d
glass ...

CoRR:
silanized
glass
beads

a b
θ=25˚ θ=93˚
•  Rolling coefficients are strongly
modified by the surface sila...

Movement
restric<on

Movement is restricted on electrified interfaces!!!
Beads on top Beads withdrawn

Fric,on
angle:
PTFE
x
PE

•  Triboelectrification
between PTFE and
PE increases
friction angles
•  Some PE ...

Polyethylene pellets PTFE
Fric,on
angle:
PTFE
x
PE

PTFE + PE pellets
after shaking PTFE
PTFE + PE pellets
...

Fric<on
at
a
microscopic
level:

Lateral
Force
Microscopy

•  First
veriﬁed
by
Mate
et...

α∆´ =
(1+µ2)sinθcosθ
cosθ2 − µ2 sin2θ
αW´ =
µ
cosθ2 − µ2 sin2θ
µ + =
2∆´
W´sin2θ
1
µ
LFM
calibra<on:

volts
(V)
...

Lateral
force
microscopy
(LFM)

•  Friction is largely affected
by surface charges at the
nanometer scale;
•  ...

Force-‐distance
curves
(Fd)
on
tribocharged
PTFE

In Geckos, each hair produces 100 nN (due to van der ...

Parcial
Conclusions

•  Tribocharges produced by friction have a large effect
on the friction coefficients of dielec...

Bipolar
Tribocharging
Signal
During

Fric3on
Force
Fluctua3ons
at

Metal–Insulator
Interfaces
...

Escobar, JV, Chakravarty, A, Putterman
SJ, Diamond Relat. Mater. 2013
Akbulut M, Godfrey
Alig AR, Israelachvili
J. J. Phys...

Setup

Tribocurrent x friction force
vacuum nitrogen
hydrogen open air
1N normal load
50 cm/s speed
PTFE x Steel

Tribocurrent(nA)
Frictionforce(N)
1N 2N 5N
5 cm/s 5 cm/s 5 cm/s
25 cm/s 25 cm/s 25 cm/s
50 cm/s 50 cm/s 50 cm/s

Results Friction force fluctuations:
ü  Fluctuations of friction force
occur with certain regularity in
tribological test...

Tribocurrent and transient friction
force fluctuation
Although tribocurrent signal depends on speed and load, charged
spec...

TRACK: negatively charged
Xerox® Cyan Developer powder (iGen3,
5R706). When placed on the sample, the track
promptly repea...

Quantitative NanomechanicsTM (QNM)
Quantitative material properties obtained by force curve analysis at
every pixel!!!
Z P...

Force distance curves
Clean PTFE
Charged PTFE

Adhesion mapping on PTFE track
Strongly adhered PTFE flakes
5 mm
Pull-off force: 150 nN
for most of the pixels!
PTFE
track...

Triboemission
(triboluminescence) under
Neon atmosphere

Burgo, T. A. L. & Erdemir, A.
Ang. Chem. Int. Ed., 53, 2014.

Concluding Remarks
n Friction force fluctuations are
always accompanied by two
tribocharging mechanisms at
metal-insulato...

Prospects:
Controlling friction?
n  The nature of the fundamental processes
that give rise to friction between sliding
bo...

Electrostatically stimulated additives?
Electrostatic potential
naturally built up at
interfaces under relative
motion sho...

Tribocurrent at the nanoscale?
In progress…
AFM contact modes could be combined
with techniques for monitoring the
triboel...

Acknowledgements
n  Department of Energy (DOE)
n  Argonne National Laboratory
–  Tribology Section
–  Center for Nanosca...

Unicamp
Instituto de
Química

“God made the bulk; surfaces
were invented by the devil.”
Wolfgang Pauli
Thank you…

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