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Article Dans Une Revue Physics today Année : 1999

On stickiness

Cyprien Gay
Ludwik Leibler
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Résumé

If you step on a used piece of chewing gum thrown away by some untidy folk, it will stick to the bottom of your shoe. It will also provide you with an apt example of undesirable stickiness. Conversely, in wrapping a package, you'll seek out stickiness in the form of adhesive tape, which is a result of long, truly interdisciplinary research which involved many physicists, chemists and engineers, both from industry and academe. What is stickiness and how is it measured ? The American Society for Testing and Materials (ASTM) definition is that a material is sticky - “tacky” in the more professional jargon - if an appreciable force is needed to separate from it immediately after contact. When you touch something sticky, it is an everyday reflex to try every possible movement to pull your finger away. Sticky materials are designed to resist all such attempts to separate, including normal pulling off, shearing, peeling. These requirements are often difficult to meet simultaneously, and so designing a truly sticky material is a matter of compromise. For instance, water is not considered to be sticky because, even though two wet microscope slides are difficult to pull apart, they can slide apart to easily. Polymer melts, made of long, flexible molecules, naturally provide the desired properties of sticky materials: under stress, at long timescales, they flow like very viscous liquids, whereas at short timescales, they deform like soft, elastic solids. The characteristic timescales can be tuned by chemical composition, chain length, and molecular architecture - for example, by using branched rather than linear chains. They also depend strongly on temperature, especially near the glass transition temperature, at which the polymer transforms progressively from a viscous melt to a solid, plastic state. By incorporating different types of monomers in the same chain, one can tune the interchain friction and the dissipative processes in the material. Controlling adhesion is important in many different fields besides adhesives: glass, tyres, wood, paper, metals, ceramics, paints, cosmetics industries often rely on it, as does even the food industry. A whole body of knowledge and understanding developed in each of these domains. Several contradictory descriptions, therefore, have come to coexist, each well adapted to a particular material. On the whole, the science of adhesion and adhesives has thus developed very nonlinearly. So the story we tell here is thematic rather than chronological.
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hal-00515441 , version 1 (07-09-2010)

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  • HAL Id : hal-00515441 , version 1

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Cyprien Gay, Ludwik Leibler. On stickiness. Physics today, 1999, 52, pp.48-52. ⟨hal-00515441⟩

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