FN [mN]

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


2

//// Nanotribometer NTR2

Manual approach (coarse and fine)

Dual beam cantilever measurement head

Table Top Platform


Microscope (option)

Linear or rotation module

Positioning tables (manual or motorized)

3

//// 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


5

//// 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:


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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


8

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


9

The moving friction partner more detailed …

SEM images of insects feet


10

//// 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]


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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


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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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