Smooth rubber sphere

A useful exercise is to compare the situation in which a liquid drop sits on a polymer surface with that of a smooth rubber sphere adhering to a glass plate, as in Fig. 7.6. 

The other source of adhesion with polymers arises from van der Waals forces and, if there are certain polar atoms present, from hydrogen bonding. We shall deal in what follows only with the former. Consider for example the contact between a smooth rubber sphere and a hard smooth flat surface. If the spheres and flat are brought... 

The first truly reversible adhesion cracking experiments were carried out by Obreimoff in 1930 on mica and by Johnson et al in 1971 using smooth elastic rubber spheres. The diameter of the black contact zone was measured in reflected light, and plotted against the applied force to compare with the thermodynamic cracking theory. The results were reasonably reversible and fitted the thermodynamic work of adhesion theory. These experiments are described more fully in Chapters 4 and 9. 

The results in Figure 4 yield a 50 50 ratio by mass when a smoothed approximation of P is used where the smoothing is performed in an attempt to remove particle refractive index as a necessary parameter. However, a better calculation, using the correct refractive index (1.545) of this particular rubber and the full Mie theory for spheres, yields a mass concentration ratio of 69 31 for the 1010nm 270nm sizes which is quite close to the 70 30 ratio of this blended sample. 

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