Binary Miscible Blends of Poly(Methyl Methacrylate)/Poly(α-Methyl Styrene-co-Acrylonitrile). IV. Relationship between Shear Flow and Viscoelastic Properties

The effect of simple shear flow on the phase behavior of poly(methyle methacrylate), PMMA, and poly(α-methyl styrene-co-acrylonitrile), PαMSAN, exhibiting an LCST-type phase diagram, has been analyzed on the basis of a generalized Gibbs free energy of mixing, G_γ̇, modified by a stored energy term, E_s. The value of the E _s, (the energy stored by the polymeric molecules during shear flow) was experimentally determined as a function of composition and shear rate from the viscoelastic material functions of the blend by using two different methods proposed by Marrucci and Wolf. The evaluated E_s (proposed by Marrucci) from the entanglement plateau modulus, G_N⁰, and dynamic shear viscosity at a given shear rate,η(γ̇), were found to well describe the behavior of shear-induced mixing for the present system; i.e., a negative deviation of E_s from the linear-mixing rule has been detected, which is a necessary condition for the elevation of the cloud points to higher values under shear flow. However, on the other hand, the calculated E_s from the viscoelastic relaxation time, τ ₀ and zero shear viscosity, η₀ (Wolf model), predicted both shear-induced mixing and shear-induced demixing for the large and small concentration range of PαMSAN, respectively; i.e., negative and positive deviation of E_s from the linear-mixing rule was observed dependent on the concentration of PαMSAN. It is concluded that the viscoelastic material functions of the blend are very helpful for qualitatively anticipating the phase behavior of the blend under the effect of shear flow.