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Adhesion paradox: Why adhesion is usually not observed for macroscopic solids
A Tiwari1, J Wang1,2, B N J Persson1
1PGI-1, FZ Jülich, Germany, Jülich 52428, European Union.
Physical Review. E
|November 20, 2020
Summary
The adhesion paradox, where objects in contact don't stick, is explained by surface roughness. Longest-wavelength roughness prevents adhesion, even for human fingers on glass.
Area of Science:
- Physics
- Materials Science
- Tribology
Background:
- The adhesion paradox describes the lack of detectable adhesion between surfaces initially in molecular contact.
- Surface roughness is a key factor influencing adhesion phenomena.
Purpose of the Study:
- To investigate the role of surface roughness in the adhesion paradox.
- To experimentally and theoretically analyze adhesion, particularly concerning the effect of roughness wavelengths.
- To examine the mechanics of finger-glass contact and adhesion.
Main Methods:
- Experimental adhesion measurements on various solid objects.
- Theoretical modeling to understand the influence of roughness on adhesion.
- Adhesion experiments involving a human finger and a glass plate under varying conditions.
Main Results:
- Longest-wavelength surface roughness was identified as the primary factor "killing" adhesion in most cases.
- No macroscopic adhesion was observed between a dry human finger and a clean glass plate.
- A decrease in contact area with increasing shear force was noted for finger-glass contact.
Conclusions:
- Surface roughness, specifically long-wavelength features, explains the adhesion paradox.
- Finger-glass contact mechanics, involving large deformations, govern the observed behavior rather than adhesion.
- The study provides insights into the fundamental principles of adhesion and contact mechanics.
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