Читать книгу The Rheology Handbook - Thomas Mezger - Страница 71

For a polymer solution in the low-shear range, the η0 value is attained only under the condition that the polymer concentration c [g/l] is high enough. Only in this case the molecule chains are able to get in contact with one another to form entanglements. For polymers having a constant molar mass and using the value of the critical concentration ccrit, the following applies (see Figure 3.11):

For c < ccrit: η/c = c1 = const

Low-concentrated, diluted polymer solutions having no effective entanglements between the individual molecule chains display ideal-viscous flow behavior, and this counts also for the low-shear range. In this case, the viscosity value is directly proportional to the concentration (with the

material-specific proportionality factor c1).

For c > ccrit applies:

For concentrated solutions and melts of uncrosslinked polymers showing effective entanglements between the individual molecule chains each of them indicates a zero-shear viscosity value in the low-shear range. With increasing concentration, there is a stronger increase of the η0-value as can be seen by the higher slope of the η(c)-function in this concentration range (see Figure 3.11).