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Boundary Lubrication with Adsorbed Anionic Surfactant Bilayers in Hard Water
Aya Toyoda1, Hikaru Kimura1, Tadashi Sugahara2
1R&D - Analytical Science Research, Kao Corporation, 1334 minato, Wakayama, Wakayama 640-8580, Japan.
Langmuir : the ACS Journal of Surfaces and Colloids
|January 10, 2025
Summary
Hydroxy alkane sulfonate (C18HAS) forms lubricating bilayer films on mica surfaces in hard water. These films exhibit extremely low friction due to slipping between alkyl chains, not headgroups.
Area of Science:
- Surface Science
- Tribology
- Colloid and Surface Chemistry
Background:
- Anionic surfactants can form complex structures like vesicles in solution.
- Surfactant adsorption on charged surfaces is influenced by solution chemistry, such as hard water ions.
- Understanding interfacial behavior is crucial for designing effective lubricants.
Purpose of the Study:
- To investigate the adsorption of hydroxy alkane sulfonate (C18HAS) onto mica from hard water.
- To characterize the resulting lubricating film structure and properties.
- To elucidate the mechanism behind the observed low friction.
Main Methods:
- Atomic Force Microscopy (AFM) for measuring adsorbed bilayer thickness.
- Surface Forces Apparatus (SFA) for evaluating friction and lubrication properties.
- Investigation of C18HAS adsorption from hard water solutions onto mica surfaces.
Main Results:
- C18HAS formed vesicles in hard water that adsorbed onto negatively charged mica via Ca2+ bridging.
- Adsorbed layers transformed into bilayer films with a time-dependent increase in thickness.
- The confined C18HAS film exhibited a friction coefficient (μ) of 10-3 or below.
Conclusions:
- The low friction arises from slipping between the liquid-like alkyl chain tails within the adsorbed bilayers.
- This slipping occurs at two distinct planes, contributing to the exceptionally low friction.
- The findings offer insights into the design of novel boundary lubricants based on surfactant self-assembly.
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