Physics – Condensed Matter – Soft Condensed Matter
Scientific paper
2008-08-29
Physics
Condensed Matter
Soft Condensed Matter
Accepted by J. Phys.: Condens. Matter, CODEF II Special Issue. 20 pages, 9 figures
Scientific paper
10.1088/0953-8984/20/40/404207
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.
Dhont Jan K. G.
Kohlbrecher Joachim
Lettinga Paul M.
Lonetti Barbara
Willner L.
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