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| Home > Publications database > Quantitative understanding of sheared colloidal rods and the effect of length and stiffness |
| Talk (non-conference) (Invited) | FZJ-2019-06117 |
2019
Abstract: Soft matter materials are classically characterized by rheological experiments, which probe the mechanical response to shear flow. Knowledge of the microscopic structure in flow is crucial to understand, predict, and tune flow behaviour and therefore the macroscopic rheological response of complex fluids. A simple example of such fluids are dispersions of stiff particles, as alignment of the particles will cause a huge drop in the viscosity of the fluid. This ‘shear thinning’ can cause flow to be unstable, causing gradient shear banding. It is yet unclear, however, how this highly non-linear behaviour is linked to microscopic features such as the stiffness and dimensions of the particles. In this talk I will first show how we gained full understanding of the shear thinning process of rods by performing in situ rheology and Small-angle neutron scattering experiments1 on a library of monodisperse viruses with varying length2. The shear and length dependent orientational order could be linked to the rheological response, by extending the Doi, Edwards, Kuzuu theory. I will also show, however, that even a length of 2 𝜇m for the longest viruses is not sufficiently shear thinning to yield the system unstable3. On the other hand, we could tune dispersions of Xanthan4 and pnipam-grafted DNA dispersions such that shear bands do form, using the ionic strength and temperature, respectively. Finally, in situ microscopy experiments on F-actin5 will be discussed to show how systems where the persistence length is smaller than the contour length relax in shear flow.
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