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arXiv · 0808.4054

Dynamic Response of Block Copolymer Wormlike Micelles to Shear Flow

B. Lonetti·J. Kohlbrecher·L. Willner·J. K. G. Dhont·M. P. Lettinga
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Abstract

The linear and non-linear dynamic response to an oscillatory shear flow of giant wormlike micelles consisting of Pb-Peo block copolymers is studied by means of Fourier transform rheology. Experiments are performed in the vicinity of the isotropic-nematic phase transition concentration, where the location of isotropic-nematic phase transition lines is determined independently. Strong shear-thinning behaviour is observed due to critical slowing down of orientational diffusion as a result of the vicinity of the isotropic- nematic spinodal. This severe shear-thinning behaviour is shown to result in gradient shear banding. Time-resolved Small angle neutron scattering experiments are used to obtain insight in the microscopic phenomena that underly the observed rheological response. An equation of motion for the order-parameter tensor and an expression of the stress tensor in terms of the order-parameter tensor are used to interpret the experimental data, both in the linear and non-linear regime. Scaling of the dynamic behaviour of the orientational order parameter and the stress is found when critical slowing down due to the vicinity of the isotropic-nematic spinodal is accounted for.

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B. Lonetti, J. Kohlbrecher, L. Willner, J. K. G. Dhont, M. P. Lettinga. 2008-08-29. Dynamic Response of Block Copolymer Wormlike Micelles to Shear Flow. https://doi.org/10.1088/0953-8984%2F20%2F40%2F404207

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