State Key Laboratory of Tribology

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Confinement-induced nano-sandwich of liquid crystal in Thin Film

Lubrication

Ming Gao, Liran Ma, Jianbin LuoState Key Laboratory of Tribology,

Tsinghua University, Beijing 100084, China

State Key Laboratory of Tribology

Outline

Background

Experiments

Results and Discussion

Future research

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State Key Laboratory of Tribology

Background3

Friction F

Surface 1

Surface 2Lubricant

Load N

Tribology is the science and engineering of interacting surfaces in relative motion. It includes the study

and application of the principles of friction, lubrication and wear.

Macroscopic tribology: Friction coefficient, Wear Rate, Lubrication.

Macroscopic

Nascimento F C, Foerster C E, Silva S L R, et al. A comparative study of mechanical and tribological properties of AISI-304 and AISI-316 submitted to glow discharge nitriding[J]. Materials Research, 2009, 12(2): 173-180.

Hwang S Y, Lee N R, Kim N. Experiment and Numerical Study of Wear in Cross Roller Thrust Bearings[J]. Lubricants, 2015, 3(2): 447-458.

http://www.jamet.com/lubrication.html

State Key Laboratory of Tribology

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Thin Film Lubrication (TFL) Physical Model

Luo J. On Experimental Technique and Characteristic of Thin Film Lubrication [D]. Doctoral dissertation, Tsinghua University, 1994.

Li J, Zhang C, Luo J. Superlubricity behavior with phosphoric acid–water network induced by rubbing[J]. Langmuir, 2011, 27(15): 9413-9417.

Li J, Zhang C, Sun L, et al. Tribochemistry and superlubricity induced by hydrogen ions[J]. Langmuir, 2012, 28(45): 15816-15823.

Nanotribology: Lubrication Mechanism at Nanoscale

Molecular structure in the lubrication film

Background

004.0

Friction c

oeffic

ient

Time (s)

Superlubricity Behavior with Phosphoric Acid

surface

fluidic layer

transition

layer

absorbed

layer

Time/s

Film

th

ickn

ess/n

m

Static state

n-decane

n-decane+ hexadecanoic acid

TFL state

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Notes：Raman Intensity is too weak;

Information of absorbed molecules on surfaces??

BackgroundIn-situ Testing Platform equipped with Raman Spectroscopy

Load：160g

Speed：31.4 mm/s

The alignment of 5CB at different stage

Lubricant: 5CB

Objective: The relationship between friction coefficient and molecular ordering

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Background

Thickness of TFL：n*10~m*100nm

Raman Spectra

Surface Enhanced Raman Spectra

Enhanced Signal

Low IntensityMolecular structure

Electromagnetic Enhancement

Chemical Enhancement

Nano Particles

Au, Ag, Cu

Li, Al, Pt

Nano structures

Au, Ag, Cu

Others

graphene

Quantum dots

Au

Ag

Suitable Substrate

SERS

substrate

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Experiments

50Xobjective

PC

P

Laser

Half-wave-plate Mirror

Analyzer

Video

Spectrometer

Apparatus

Raman Spectroscopy

Silica plate

Rotating

Lubricant

Steer ball

Load applied

Ball-on-disk

Silica plate

Rotating

LubricantConvex lens

covered

with Ag film Load applied

Fric

tion

Pla

tform

SERS

Effect

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Experiments-Fabrication of SERS substrate

Ag nanorod

Evaporation Flow

K9 lens

Electron Beam Evaporation

——oblique angle deposition (OAD) technique

Evaporation Flow

α

50nm Ti Film 500nm Ag Nanorods film

1mm 500nm

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Results and DiscussionSERS Effect Detection Lubricant: 6CB (p-n-hexyl-p’-cyanobiphenyl, C6H13(C6H6)2CN)

On K9 Lens

2230cm-1C-N bond

Silver surface

6CB

Ag Nanorod

SERS Effect：3~5nm near Surface

Absorption

SERS Spectra came from

molecules absorbed on

the surface

State Key Laboratory of Tribology

10Results and Discussion

Measurement Method：Orientation of 6CB molecules

0°

Orientation of 6CB could be obtained by calculating

the polarization anisotropy of the C-C aromatic

vibration mode of 6CB at 1606 cm-1.

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Results and DiscussionOrientation of absorbed 6CB molecules during shearing

Ag nanorods

Shearing

Static State 30s after shearing 400s after shearing

Point 1 Point 1

Point 2

Point 1

Point 1 Point 1 Point 1

Po

int 2

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Results and DiscussionMorphology of Ag nanorods during shearing

Static State 30s after shearing 400s after shearing

Structure of silver film is related to the orientation molecules in measured 6CB nano film.

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Results and DiscussionOrientation of absorbed 6CB molecules on Ag nanorods

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Results and DiscussionOrientation of absorbed 6CB molecules on different substrates

Orientation of 6CB

in the whole

lubrication film

Orientation of 6CB

in the absorbed

film

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Results and Discussion

Thin Film Lubrication (TFL) Molecular pattern

Shearing

Tilted Ag nanorods

Fluidic Layer:

Absorbed Layer: 3nm(Measured by Relative Light

Intensity Principle)

X

YZ

Shearing

Surface Absorption

Shearing Force

Transition Layer

TFL Model

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