Non-newtonian behavior of polymers with log-normal molecular weight distribution

By choosing suitable approximations to Bueche's function, it is possible to calculate the viscosity versus shear stress for log-normal molecularly distributed linear polymers. For bulk polymers the mixing rules M?_w, M?_w, M?_z are considered. For values of η/η0 > 0.1 and heterogeneities with M?_w/M?_n > 1.5 the result obtained with any mixing rule is η/η0 = erfc (1/delta;) log (M₀Q^h/aK)], where a = π²/6_pRT and where the δ and K values are dependent on the heterogeneity ratio Q = M?_w/M?_n and on the type of mixing rule; on the other hand, the h value is independent of the heterogeneity, but depends on the mixing rule. Most experimental data should fit the M?_w mixing rule as one would expect from the zero shear stress mixing rule. Experimental data are compared with the theoretical results.