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Ensemble Force Spectroscopy by Shear Forces

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Compliant Surfaces under Shear: Elastohydrodynamic Lift Force.

Pierre Vialar^1,2, Pascal Merzeau^1,2, Suzanne Giasson³

¹CNRS, Centre de Recherche Paul Pascal (CRPP), UMR 5031 , F-33600 Pessac , France.

Langmuir : the ACS Journal of Surfaces and Colloids

|August 14, 2019

Summary

We studied how poly(N-isopropylacrylamide) microgel coatings on mica surfaces behave under shear. These coatings generate lift forces, enabling hydrodynamic lubrication and offering control over friction and wear.

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Area of Science:

Tribology
Materials Science
Surface Chemistry

Background:

Mica surfaces are widely used in tribological studies.
Poly(N-isopropylacrylamide) (PNIPAM) microgels are stimuli-responsive polymers with tunable properties.
Understanding lubrication mechanisms is crucial for reducing friction and wear in various applications.

Purpose of the Study:

To investigate the tribological behavior of mica surfaces coated with cationic poly(N-isopropylacrylamide) microgels under shear and compression.
To explore the emergence of shear-induced normal forces and their impact on lubrication regimes.
To quantify the lift force generated by these microgel-coated surfaces.

Main Methods:

Utilized a tribometer to apply shear and compression to mica surfaces coated with PNIPAM microgels.
Implemented a feedback-loop control system to precisely manage surface separation.
Measured velocity-dependent normal forces and lift forces as a function of surface separation and driving speed.

Main Results:

Observed velocity-dependent, shear-induced normal forces that can lead to surface separation.
Demonstrated the transition from boundary to hydrodynamic lubrication due to entrained fluid films.
Quantified the lift force, showing its dependence on surface separation and driving speed.

Conclusions:

Elastohydrodynamic effects are significant in the lubrication of compliant, microgel-coated surfaces.
The observed lift forces provide a mechanism for controlling friction and wear.
This study offers insights into designing advanced lubrication strategies using responsive polymer coatings.