Contact between rough surfaces and a criterion for macroscopic adhesion

At the molecular scale, there are strong attractive interactions between surfaces, yet few macroscopic surfaces are sticky. Extensive simulations of contact by adhesive surfaces with roughness on nanometer to micrometer scales are used to determine how roughness reduces the area where atoms contact...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2014-03, Vol.111 (9), p.3298-3303
Main Authors: Pastewka, Lars, Robbins, Mark O.
Format: Article
Language:English
Subjects:
Adhesion
Adhesiveness
Adhesives
Atomic interactions
Atoms
Contact loads
Elasticity
Fractals
Friction
Mathematical surfaces
Models, Theoretical
Numerical analysis
Physical Sciences
Physics
Simulation
Stiffness
Surface Properties
Surface roughness
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Summary:At the molecular scale, there are strong attractive interactions between surfaces, yet few macroscopic surfaces are sticky. Extensive simulations of contact by adhesive surfaces with roughness on nanometer to micrometer scales are used to determine how roughness reduces the area where atoms contact and thus weakens adhesion. The material properties, adhesive strength, and roughness parameters are varied by orders of magnitude. In all cases, the area of atomic contact is initially proportional to the load. The prefactor rises linearly with adhesive strength for weak attractions. Above a threshold adhesive strength, the prefactor changes sign, the surfaces become sticky, and a finite force is required to separate them. A parameter-free analytic theory is presented that describes changes in these numerical results over up to five orders of magnitude in load. It relates the threshold adhesive strength to roughness and material properties, explaining why most macroscopic surfaces do not stick. The numerical results are qualitatively and quantitatively inconsistent with classical theories based on the Greenwood−Williamson approach that neglect the range of adhesion and do not include asperity interactions.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1320846111