Why pens have rubbery grips

The process by which human fingers gives rise to stable contacts with smooth, hard objects is surprisingly slow. Using high-resolution imaging, we found that, when pressed against glass, the actual contact made by finger pad ridges evolved over time following a first-order kinetics relationship. Thi...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS Vol. 114; no. 41; p. 10864
Main Authors: Dzidek, Brygida, Bochereau, Séréna, Johnson, Simon A, Hayward, Vincent, Adams, Michael J
Format: Journal Article
Language:English
Published: United States 10.10.2017
Subjects:
Adult
Elastomers - chemistry
Female
Fingers - physiology
Friction
Glass - chemistry
Hand Strength - physiology
Humans
Skin - chemistry
Surface Properties
Sweat Glands
Touch - physiology
biotribology
finger friction
true contact area kinetics
fingerprints
ISSN:1091-6490, 1091-6490
Online Access:Get more information
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Summary:The process by which human fingers gives rise to stable contacts with smooth, hard objects is surprisingly slow. Using high-resolution imaging, we found that, when pressed against glass, the actual contact made by finger pad ridges evolved over time following a first-order kinetics relationship. This evolution was the result of a two-stage coalescence process of microscopic junctions made between the keratin of the stratum corneum of the skin and the glass surface. This process was driven by the secretion of moisture from the sweat glands, since increased hydration in stratum corneum causes it to become softer. Saturation was typically reached within 20 s of loading the contact, regardless of the initial moisture state of the finger and of the normal force applied. Hence, the gross contact area, frequently used as a benchmark quantity in grip and perceptual studies, is a poor reflection of the actual contact mechanics that take place between human fingers and smooth, impermeable surfaces. In contrast, the formation of a steady-state contact area is almost instantaneous if the counter surface is soft relative to keratin in a dry state. It is for this reason that elastomers are commonly used to coat grip surfaces.
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ISSN:1091-6490
1091-6490
DOI:10.1073/pnas.1706233114