The influence of shear on the ordering temperature of a triblock copolymer melt

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Abstract
The effect of shear on the ordering temperature of a triblock copolymer melt of polystyrene‐polybutadiene‐polystyrene (SBS) is examined by in situ small angle neutron scattering (SANS). Results obtained by SANS are compared to the rheologically determined order–disorder transition temperature, TRODT=115±5 °C. The SANS measurements from a Couette geometry shear cell are then used to construct a ‘‘dynamical phase diagram’’ based on characteristic changes in the scattering with temperature and shear rate, γ̇. A shear rate dependent ordering temperature, Tord(γ̇), is identified as the system is sheared isothermally from the disordered state. The scattering behavior is shown to be highly strain dependent. We compare our findings on the shear rate dependence of the ordering transition in triblock materials with previous observations on diblock copolymer materials and theoretical expectations for the shear rate dependence of the order–disorder transition temperature. A simple scaling argument leads to a good description of the shear rate dependence of Tord(γ̇) in both diblock and triblock copolymer measurements over the range of shear rates examined.