VISCOELASTIC PROPERTIES OF IMMISCIBLE POLYMER BLENDS UNDER STEADY ANDTRANSIENT SHEAR FLOWS

Viscoelastic properties of binary blends of immiscible polymers with a lmost the same viscosity were studied under steady and transient shear flows in the light of the scaling relations in the constitutive equat ion of textured materials presented by Doi and Ohta. Samples used were blends of polydimethylsiloxane (PDMS) and polybutadiene (PB) with the composition ratios of 3:7, 1:1, 7:3, and 9:1 for PDMS:PB by weight. I t was found that both shear stress sigma12 and primary normal stress d ifference N1 at steady state are proportional to shear rate gamma exce pt N1 of 9:1 blend, and the rescaled transient stresses after stepwise increase of shear rate compose a single line in terms of strains if t he step ratios of shear rates are constant, in accordance with the sca ling relations. For the 9:1 blend, in which the contribution of N1 of component polymers cannot be neglected because the interface is small, however, the extra primary normal stress difference at steady state a fter subtracting N1 of component polymers from the measured one was fo und to be proportional to gamma in accordance with the scaling relatio ns.