Viscoelastic properties of low molecular weight symmetric poly(styrene-b-2-vinylpyridine)s in the ordered and disordered states under steady shear flow

Viscoelastic properties of symmetric poly(styrene-block-2-vinylpyridine)s in the ordered and disordered states under steady shear flow are examined for relatively low molecular weight samples at melt based on the temperature dependence of interaction parameter x. Since both components have almost the same viscoelastic properties, data for block copolymers and components are directly compared. In the disordered state near the ODT, two constant values for shear viscosity η, η°₁ and η°₂ at lower and higher shear rates, γ, respectively are obtained for diblock samples and η°₁ coincided with the value obtained by dynamic flow measurements, which are higher than the values for components. The constant values of J_e are obtained at γ range where η°₂ are obtained, which are also higher than those of components. It was concluded that higher η°₁ and lower η°₂ values are due to the fluctuation effects and their suppression by the flow with higher γ, respectively. It was also concluded that fluctuation effects on viscoelastic properties completely disappear at around xN< 2 - 3 for SPs. In the ordered state, well aligned state was only attained for the sample having lowest molecular weight. The values of η° and J_e obtained in well aligned state are consistent with those in disordered state, denoting that there is no discontinuity of data due to ODT.