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| Home > Publications database > In situ large amplitude oscillatory shear (LAOS) experiments on rod-like viruses and colloidal platelets |
| Home > Publications database > In situ large amplitude oscillatory shear (LAOS) experiments on rod-like viruses and colloidal platelets |
| Conference Presentation (Other) | FZJ-2013-01963 |
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2012
Abstract: Highly anisotropic particles are by nature susceptible to external fields. In particular shear forces can cause a pronounced shear thinning, where a highly viscous unordered system is sheared into a low viscous ordered system. This makes shear thinning behavior both fundamentally and practically interesting. The rheological and structural responses of the system at the onset of shear thinning can be conveniently studied by large amplitude oscillatory shear (LAOS) in combination with in situ scattering techniques. Here we study two systems: 1) dispersions of rod-like (fd) viruses approaching the isotropic - nematic transition in combination with time-resolved small-angle neutron scattering; 2) dispersions of gibbsite platelets around the nematic phase in combination with time-resolved small-angle X-ray scattering. Viewing the responses as indicating a sequence of physical processes, we identify, for the rod-dispersions, a region of purely elastic response accompanied by an increase in the orientational ordering. By yielding this is followed in sequence by a region of fluid-like behavior at an almost constant ordering. The platelet dispersions display, for a broad range of frequencies, a transition from singlet feature in the scattering at small strain amplitude to a doublet at large strain amplitude. This suggests the existence of a critical strain for reorienting the platelets, which is not reflected in the bulk rheology.
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