The Adhesion Paradox

INTRODUCTION TO MOLECULAR ADHESION AND FRACTURE THE ADHESION PARADOX... 

Solving the problem of the adhesion paradox during the last century has brought a new understanding to the field of adhesion. We now appreciate that... 

With amine hydrochlorate, the problem is still more paradoxical. The adhesion tensions are negative and their absolute values may, in a high dope concentration, be equal to the value of the interfacial tension, but of opposite sign. The solid is, therefore, perfectly wetted by water. 

Jung H, Toth PT, White PA, Miller RJ (2008) Monocyte chemoattractant protein-1 functions as a neuromodulator in dorsal root ganglia neurons. J Neurochem 104 254-263 Kahn L, Alonso G, Normand E, Manzoni OJ (2005) Repeated morphine treatment alters polysia-lylated neural cell adhesion molecule, glutamate decarboxylase-67 expression and ceU proliferation in the adult rat hippocampus. Em J Nemosci 21 493-500 Kaul M, Ma Q, Medders KE, Desai MK, Lipton SA (2007) HIV-1 coreceptors CCR5 and CXCR4 both mediate neuronal cell death but CCR5 paradoxically can also contribute to protection. Cell Death Differ (2) 296-305... 

Therefore we have to decide what is the most fundamental nature of matter. Does it stick or not We can short-cut to the answer given in ChaptCT 3. The first Law of Adhesion is that All atoms adhere with considerable force. This is as strange and surprising as the law of motion enunciated by Newton. How could our world operate if all the atoms were stuck fast and immobilized Cars would not work because the tires would stick to the road. Indeed, the car engine parts would all seize together and stop moving. The paradox is that the car is made up of thousands of parts, most of which do stick together rather well. But some do not. This book sets out to explain this paradox. 

Thus the paradox of adhesion being unpredictably large or small can be explained by these two complexities of contact at the molecular level contamination and toughness. 

The question of what happens when a bunch of particles comes together was asked by Newton, who found the process diffieult. Yet if aU particles adhere strongly as described above, they should leap into contact, then deform and squash closer to each other as a result of molecular adhesion. It is a paradox that particles which adhere sttongly do not do this. Instead they form weak, loose treelike structures because each particle sticks where it touches, as shown in Fig. 9.19(a). This instant adhesion therefore prevents good compaction, which can only be achieved if the particles do not adhere strongly but can wander around to find dense close-packing positions. Fig. 9.19(b). 

These results also show a paradoxical behavior of chemical modification to adhesion. Crosslinking the polymer improves the molecular weight effect at the... 

Nearly a century after Fairbaim, in 1938, two ideas emerged from the new engineering of airframes which were to focus on the paradoxical notion embodied in Equations (15.1) and (15.2). Volkersen derived a stress analysis for the deformation of a lap joint, showing that infinite stresses could arise at the ends of a lap joint, and Chadwick measured the peel strength of soldered joints, raising the conundrum that a joint is much weaker in peeling than it is when overlapped. How can strength be different when the same adhesive is employed ... 

It is the authors opinion that these physical responses arc best controlled by providing a stable environment through the careful monitoring of temperature and humidity. Therefore one may say that the final constraint (paradoxical as it may seem) is to use an adhesive that does not alter the paintings previous response to climatic variations, though act as a structural support. In order to understand just exactly what these responses are requires not only an understanding of the chemical and physical properties of artist s materials but how their chemical and physical aging effects these properties over time. 

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