Nonlinear Melt Rheology of Lamellae Forming Polystyrene‐b‐Poly‐2‐Vinylpyridine Diblock Copolymers

Abstract

AbstractLamellae forming polystyrene‐b‐poly‐2‐vinylpyridine diblock copolymer melts are investigated with linear shear rheology and Fourier transformation rheology (FT rheology) to quantify their nonlinear behavior under oscillatory shear via mechanical higher harmonic contributions such as I3/1(ω1, γ0). The determination of the zero‐shear nonlinearity () by a variation of γ0 is hindered by the increasing domain alignment at increasing γ0. Thus, an approach for determining 3Q0(T) by a variation of the temperature is developed and used. This approach allows obtaining insights on the nonlinear behavior directly at temperature‐dependent phase transitions, such as at the order‐disorder transition temperature TODT of block copolymers. The maximum of 3Q0 is found to be close to TODT. The nonlinearity originating from the connection of the unequal polymer blocks is shown to dominate the overall nonlinearity, and the maximum of 3Q0(T) correlates to  domain alignment for T < TODT.