ON THE VISCOSITY-CONCENTRATION DEPENDENCE OF IMMISCIBLE POLYMER BLENDS

Upon addition of small quantities of a second phase the mixture shows a droplet/matrix structure, changing into a co-continuous one at the percolation threshold, phi-c approximately equal to 0.16. The level of phase co-continuity reaches a maximum at the phase inversion concentration, phi-2I, where the viscosities of a system in which polymer-1 is dispersed in polymer-2 and the other where polymer-2 is dispersed in polymer-1 are equal. Thus phi-1I can be expressed as function of viscosity ratio, lambda = eta-1/eta-2, with intrinsic viscosity and maximum packing volume fraction as parameters. Next, it was postulated that in immiscible polymer blends the viscosity-concentration dependence is determined by two mechanisms: an interlayer slip and the emulsionlike viscosity increase culminating at the inversion concentration, eta-2I. The derived two-parameter equation was found to describe the observed eta-versus phi-dependence quite well. The parameters, calculated from the least-squares regression fit of experimental data to the two-parameter equation, were found to provide insight into the flow mechanism.