CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012.
Recent advances in characterization of soft materials by a new nanotribological ...
Recent advances in characterization of soft materials by a new nanotribological tool Jiri Nohava, Philippe Kempé CSM Instruments
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
//// Classification of the „Nanotribometer“ instrument line
Macro Tribometer1: • Radius: 1.5 – 10 mm • Load range: 1 – 60 N
Standardtribometer
Nanotribometer1: Nanotribometer NTR 2
• Radius:
0.5 – 2 mm • Load range: 0.01 – 1000 mN
AFM2:
AFM
• Radius:
2 – 100 nm • Load range: 1 – 50 nN
10
100
1.000
10.000
100.000
p*max in [MPa] 1) CSM product 2) Commercial standard
* Hertzian contact: Ball-disc, Al2O3-ball in contact with 100Cr6 substrate
* *
(1)
(2)
(3)
a: Contact radius, Fn: Normal force, E: Young’s modulus, : Poisson’s ratio, 1,2: Materials in contact
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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//// Nanotribometer NTR2
Manual approach (coarse and fine)
Dual beam cantilever measurement head
Table Top Platform
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
Microscope (option)
Linear or rotation module
Positioning tables (manual or motorized)
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//// NTR2 : Fn & Ft Capacitive sensors
Fn
Ft Load application and measurement > Dual beam cantilever calibrated in lateral and normal stiffness > Capacitive sensors with the highest resolution and linearity
> More linear deflection during force application > Simultaneous measurement of normal and friction force > Measurement of positive and negative normal forces (adhesion) © CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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//// NTR2: Rotative and linear module
Rotative POD Module: > Speed: max 200 rpm, min 1 rpm > Angular sensor > One way or reciprocating mode
Linear Module: > Stroke: max 5 mm or 2 mm, min 2 µm
> Voice-coil actuator & LVDT sensor > Sinusoïdal or triangular (constant speed) stroke
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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//// NTR2: List of cantilevers and force ranges
High Friction* Ft = Fnx5
Standard Ft = Fn
Low Load 10 mN
Standard Load 100 mN
HR-H
ST-H
Fn: 10 mN Ft: 50 mN
Fn: 100 mN Ft: 500 mN
HR
ST
HL
Fn: 0.1 - 10 mN Ft: 0.1 - 10 mN
Fn: 1 - 100 mN Ft: 1 - 100 mN
Fn: 0.01 - 1 N Ft: 0.01 - 1 N
ST-L
HL-L
Fn: 100 mN Ft: 20 mN
Fn: 1 N Ft: 200 mN
Low Friction* Ft = Fn/5
High Load 1N
Balls - different diameters: 1, 1.5, 2 mm - different materials: 100Cr6, Sapphire, Al2O3, Si3N4, WC, etc. © CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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//// Contact Lenses
Contact Lens Frictional Behavior in Ambient and Liquid Environments
Sample:
Contact Lens
Contact Lens
Environment:
Ambient
Liquid
LinearReciprocating
LinearReciprocating
Normal Load (mN):
4.5
4.5
Frequency (Hz):
0.2
0.2
Testing Time (s)
100
100
Number of Cycles
20
20
Stroke Length (µm)
90
90
3mm Ruby
3mm Ruby
Mode:
Static Partner:
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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//// Contact Lenses – experimental setup & results
0.15
Coefficient of Friction (µ)
0.1
0.05
0 0
20
40
60
80
100
-0.05
-0.1
-0.15
Displacement in X direction (µm)
Cycle explorer view > Coefficient of friction evolution during one or more cycles > CoF ~0.1 > High repeatability
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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Live biological tissues Tribomeasurements with grasshoppers FN: ~ 2 mN
Grasshopper
“Disc”: foot with adhesion pads
Pin: 2 mm pin with glued 3 mm ruby ball
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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The moving friction partner more detailed …
SEM images of insects feet
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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//// Live biological tissues – results Preliminary results (constant speed, increasing normal force): Extremely high coefficient of friction (~30) 0,5 0,45 0,4 0,35
FT [mN]
- FT > FN - µmax ~ 30!
0,3 0,25 0,2 0,15 0,1 0,05 0
-0,1
-0,09
-0,08
-0,07
-0,06
-0,05
-0,04
-0,03
-0,02
-0,01
0
FN [mN]
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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//// PDMS Coefficient of friction: air versus water – AIR or WATER (dry / lubricated conditions) – 500 to 600 cycles (approx. 6 to 9 m) – 5 mN normal load – Ruby ball 2 mm – Linear speed 2 cm/s – Rotative mode – Wear track radius 2 mm
AIR: Coefficient of friction ~1.05 WATER: coefficient of friction ~0.05
Influence of lateral forces caused by spinning in water? © CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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//// Lateral (friction) force measurement without contact Lateral force measurement in water and air Special conditions: Fn start at 5 mN Then the ball was lifted – normal force feedback disabled Ball in water (or air): Fn = 0 mN
© CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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//// Comparison of friction force in contact and at zero normal force
AIR (Fn = 5 mN): Ft ~ 5 mN
WATER (Fn = 5 mN): Ft ~ 0.5 mN WATER (no contact, Fn = 0 mN): Ft ~ 0.01 mN AIR (no contact, Fn = 0 mN): Ft < 0.01 mN © CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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PDMS Nanoindentation – PDMS in air – Nanoindentation with similar maximum pressure as nanotribological experiments – Spherical indenter with diameter of 200 mm – Fmax ~ 0.1 mN
– Eit ~ 1 MPa
– Pull-in, pull-off adhesion – To be performed: adhesion in water © CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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Summary and conclusions – The new Nanotribometer2 responds to the growing need of applying low pressures during tribological testing – Suitable for characterization of frictional properties of soft materials – Testing of contact lenses allows comparison of their coefficient of friction in dry and lubricated conditions
– Careful handling allows also testing of live ‘samples’ to study such effects as high CoF of grasshopper foot beds – Polymers can be tested for frictional properties at similar pressure conditions as during nanoindentation – both in dry and lubricated conditions – Future work will compare adhesion effects in air and in water during indentation and CoF measured by nanotribometer © CSM Instruments – Jiri Nohava – SwissTrib (Applied Tribology) – 17. April 2012
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