Emulsion models and rheology of filled polymers

The rheological behavior of narrow polybutadiene samples filled with rigid silica spheres has been investigated. Generally the rheological behavior of biphasic blends of polymers can be interpretated in terms of emulsion models when the concentration of the dispersed phase is low enough so as to avoid interparticle interactions. The main feature is the presence of a relaxation domain which appears in the low frequency zone of the complex shear modulus. The most general emulsion model proposed by Palierne [Palierne, J. F., Rheologica Acta, 1991, 30, 497.] explains that occurrence by the shape relaxation of the viscoelastic dispersed phase. But the model fails when the dispersed phase is very little deformable or non deformable (mineral fillers). Nevertheless a slow relaxation process is also seen experimentally in that case which can not be assumed due to shape relaxation. Those slow relaxation processes were measured and analyzed asa function of polybutadiene molecular weight and size and volume concentration of the silica spheres. They have been interpretated by an adsorption of polybutadiene chains on the silica surface that creates a monomolecular layer whose thickness is comparable to the bulk radius of gyration of the chains and whose relaxation time scales in the same way as branches of star polymers. (C) 1998 Elsevier Science Ltd. All rights reserved.