The Viscosity and Structure Viscosity of Rubber Solutions and Emulsions

Abstract

Abstract It is well known that the increase of viscosity of a colloidal solution over that of the pure solvent is produced by the frictional resistance to flow of the dispersed particles. The amount of this viscosity increase depends to a great extent on the shape of the particles. If these are spheres, only the ratio of the volume of the solute to the solvent is involved (Einstein's law), while in the other extreme case, namely with fiber molecules, the particle size plays such an important role, as is known, that one can calculate the particle weight of the dispersed phase from the viscosity (Staudinger's law, Mark-Houwink equation). But not only is the viscosity of a colloidal solution influenced by the particle form, but also its structural viscosity depends on it to a great degree. It is easy to understand this. For if the structure viscosity and, consequently, the decrease of viscosity with increasing velocity gradient, result from the fact that the hydrodynamic forces in the flowing solution, on the one hand, orient and distort the dispersed particles in the moving stream, and, on the other hand, oppose an eventual intermolecular mutual effect or aggregate formation of the particles, it is easily seen that the flow forces will be able to manifest these effects all the more readily and markedly the more extended and the stiffer the dispersed particles are. Thus it can be expected that, in general, in spherical particle suspensions no structural viscosity will appear, but that this will manifest itself the more strongly the more asymmetric the particles. With rubber it is easily possible to realize two extremely different dispersion forms. Rubber emulsions, as they exist in the various latexes, are typical definite spherical suspensions, with rather large particles of very uniform size. In rubber solutions, on the other hand, say in toluene or benzene, there is a macromolecular distribution. The dispersed particles are the individual kinky fiber molecules of the rubber, which are known to have a more or less elongated form. In fact these two types of rubber dispersions behave so differently that each of them can be called a typical representative of its class.