On Pastewka & Robbins' criterion for macroscopic adhesion of rough surfaces

TL;DR

This paper critically examines Pastewka & Robbins' criterion for macroscopic adhesion of rough surfaces, revealing its relation to asperity models and discussing potential inaccuracies and implications for surface stickiness predictions.

Contribution

It clarifies the connection between Pastewka & Robbins' criterion and asperity models, highlighting potential errors and the counterintuitive implications for surface adhesion.

Findings

Criterion aligns with asperity models at small bandwidth lpha

Potential plotting errors may affect data interpretation

Results remain inconclusive on surface stickiness predictions

Abstract

Pastewka & Robbins (PNAS, 111(9), 3298-3303, 2014) recently have proposed a criterion to distinguish when two surfaces will stick together or not, and suggested it shows a large conflict with asperity theories. It is found that their criterion corresponds very closely to the Fuller and Tabor asperity model one when bandwidth {\alpha} is small, but otherwise involves a rms ampliture of roughness reduced by a factor Sqrt({\alpha}). Therefore, it implies the stickiness of any rough surface is the same as that of the surface where practically all wavelength components of roughness are removed except the very fine ones, which is perhaps counterintuitive. The results are therefore very interesting, if confirmed. Possible sources of approximations are indicated, and a significant error is found in plotting the pull-off data which may improve the fit with Fuller and Tabor. However, still they show finite pull-off values in cases where both their own criterion and an asperity based one seem to suggest non stickiness, and the results are in these respects inconclusive.