The Connection between Biaxial Orientation and Shear Thinning for Quasi-Ideal Rods

Abstract

Abstract:The complete orientational ordering tensor of quasi-ideal colloidal rods is obtained as a function of shear rate by performing rheo-SANS (rheology with small angle neutron scattering) measurements on isotropic fd-virus suspensions in the two relevant scattering planes, the flow-gradient (1-2) and the flow-vorticity (1-3) plane. Microscopic ordering can be identified as the origin of the observed shear thinning. A qualitative description of the rheological response by Smoluchowski, as well as Doi-Edwards-Kuzuu theory is possible, as we obtain a master curve for different concentrations, scaling the shear rate with the apparent collective rotational diffusion coefficient. However, the observation suggests that the interdependence of ordering and shear thinning at small shear rates is stronger than predicted. The extracted zero-shear viscosity matches the concentration dependence of the self-diffusion of rods in semi-dilute solutions, while the director tilts close towards the flow direction already at very low shear rates. In contrast, we observe a smaller dependence on the shear rate in the overall ordering at high shear rates, as well as an ever-increasing biaxiality.

A quest for shear banding in ideal and non ideal colloidal rods

“…The slope of the curves in this low shear rate regime corresponds to the low shear viscosity. Note that this low shear viscosity should not be confused with the zero shear viscosity despite the fact that it shows a similar trend, because the zero shear viscosity is not measurable for the given systems, as has been shown in a previous paper (Lang et al 2016). Figure 3 shows that the shear thinning coefficient in this region decreases with increasing length of the particles.…”

Effects of particle stiffness on the extensional rheology of model rod-like nanoparticle suspensions

“…For suspensions of virus particles, only limited rheological data is available. Steady shear rheology was reported by Lang et al, 42 while other studies focus on the scaling of the material functions with particle concentration, 43,44 salt concentration, 45 and the detection of the suspension to gel transition. 10,11 Close to the I-N transition, these systems were also interesting model systems to investigate shear banding phenomena.…”

Microstructural Understanding of the Length- and Stiffness-Dependent Shear Thinning in Semidilute Colloidal Rods

“…and all other elements of the rotation tensor are zero. 26 Finally, we obtain the actual order parameter < P 2 > from the largest eigenvalue of the full tensor S.…”

“…23 These systems have proven to be ideally suited to study the flow behavior of rods. 18,[24][25][26][27][28] It is equally important to perform experiments that can relate the flow induced orientational ordering with the rheological behaviour of the different systems. In-situ small angle neutron scattering in combination with rheology (rheo-SANS) is particularly suited to obtain this relation 26,27,29 because of the high contrast of this technique.…”