Nonlinear rheology of immiscible polymer blends: Step strain experiments

Relaxation experiments after simple shear flow were performed on (50/50) PB/PDMS poly(1-butene)/polydimethylsiloxane immiscible model blends and the results were compared to the predictions of the Doi–Ohta and Lee–Park models. Three situations of flow were examined: (i) first the variation of stress relaxation was followed in time at various step strain amplitudes, (ii) variation of stress relaxation as a function of the amplitude of preshear rate at a fixed strain, and (iii) at a fixed strain and preshear rate, the relaxation of the stress was studied as a function of the time elapsed between the end of the preshear and the step strain. After application of step strains of various magnitudes, the stress relaxation modulus G(t,γ) at short times was found to obey the Wagner time-strain separability [Wagner (1976)]. It was possible to separate linear effects from the nonlinear ones via a damping function h(γ) of sigmoidal form. After cessation of steady shear flow of different magnitudes, the linear stress ...