SHEAR RHEOMETRY OF POLYDIMETHYLSILOXANES - MASTER CURVES AND TESTING OF GLEISSLE AND YAMAMOTO RELATIONS

This study concerns the shear rheometry of a series of nine silicone f luids, all linear or branched polydimethylsiloxanes (PDMS), with varyi ng mass distributions. The use of a rotative rheometer enabled charact erization of these products in a dynamic regime for about five decades of pulsation omega. In addition, because of the use of rotative rheom eters together with a capillary rheometer with controlled piston speed , the behavior of these products could be determined for about six ord ers of magnitude of shear rate lambda, notably for the permanent regim e viscosity coefficient eta. On the other hand, to obtain the variatio ns of the first normal stress difference coefficient psi1, over a sign ificant range of shear rate gamma, it was necessary to complete the ex perimental measurements by using empirical relations. Particularly, af ter having defined the application conditions, the Gleissle and Yamamo to relations were tested for these products. Finally, all the results obtained in dynamic and in transitory regimes by using the rheometers and empirical relations mentioned above were combined in dimensionless form. Indeed, the existence of master curves for the linear and branc hed PDMS was demonstrated. Our study therefore enables the validity of the master curve method, initially established for a series of linear monodisperse polystyrenes, to be extended to the case of a family of linear or branched PDMS of wide mass distribution.