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Published on: April 10, 2017
Dynamic phase transitions in confined lubricant fluids under shear
1Department of Chemical Engineering, Materials Department, and Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA.
Summary
Researchers studied friction in branched hydrocarbon squalane films. They found that branched liquids exhibit longer relaxation times, influencing transitions between stick-slip and smooth sliding states.
Area of Science:
- Tribology
- Materials Science
- Physical Chemistry
Background:
- Understanding friction at the molecular level is crucial for designing advanced materials and lubrication systems.
- Hydrocarbon films, particularly branched ones like squalane, present unique challenges due to their complex molecular structures and relaxation dynamics.
Purpose of the Study:
- To investigate the transient and steady-state friction forces in thin films of squalane (C30H62), a branched hydrocarbon.
- To determine the dynamic friction phase diagram and analyze transitions between stick-slip and smooth sliding states under varying shear conditions.
- To elucidate the physical reasons behind different friction behaviors observed in spherical, linear, and branched hydrocarbon films.
Main Methods:
- Utilized a surface force apparatus to measure friction forces between molecularly smooth mica surfaces.
- Confined thin films of squalane between the mica surfaces.
- Applied different shearing conditions to observe transient and steady-state friction behaviors.
Main Results:
- Characterized a chaotic stick-slip regime during dynamic friction.
- Demonstrated that branched hydrocarbon films exhibit significantly longer relaxation times and characteristic length scales compared to linear or spherical films.
- Observed distinct differences in friction traces attributed to the molecular architecture of the fluids.
Conclusions:
- The observed differences in friction traces for various hydrocarbon films are primarily due to longer relaxation times in branched liquids.
- These findings have significant tribological implications for understanding and controlling friction in complex fluid systems.
- The study provides insights into the physical mechanisms governing transitions between different sliding states in confined thin films.
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