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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
Published on: May 15, 2017
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Boundary lubrication with a liquid crystal monolayer
W Chen1, S Kulju2, A S Foster1
1COMP Centre of Excellence, Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 AALTO, Espoo, Finland.
Summary
Boundary lubrication of liquid crystal (LC) monolayers shows stick-slip behavior at low shear rates due to molecular ordering. At high shear rates, smooth sliding occurs as the LC monolayer cannot reorder.
Area of Science:
- Tribology
- Materials Science
- Condensed Matter Physics
Background:
- Boundary lubrication is crucial for reducing friction and wear between surfaces.
- Liquid crystals (LCs) exhibit unique orientational properties that can influence tribological behavior.
- Understanding molecular-level friction mechanisms is key to designing advanced lubricants.
Purpose of the Study:
- To investigate the boundary lubrication characteristics of a liquid crystal (LC) monolayer.
- To correlate friction force with the orientational order of LC molecules under shear.
- To explore the influence of surface structure and shear rate on lubrication regimes.
Main Methods:
- Nonequilibrium molecular dynamics simulations were employed.
- A simplified rigid bead-necklace model for LC molecules was utilized.
- LC monolayers were simulated between crystalline surfaces with varying atomic structures and shear rates.
Main Results:
- Stick-slip events at low shear rates were linked to molecular order-disorder transitions.
- A smooth sliding regime was observed at high shear rates due to insufficient time for LC reordering.
- An intermediate irregular stick-slip phase was identified, independent of surface structure.
Conclusions:
- The lubrication regime of LC monolayers is strongly dependent on shear rate and molecular ordering.
- Surface structure and shear rate interplay to dictate friction dynamics.
- LC monolayers offer tunable boundary lubrication properties through controlled shear conditions.
