Paper Number
SC27 

Session
Suspensions, Colloids, and Granular Materials

Title
Quantitative understanding of sheared colloidal rods and the effect of particle size and flexibility

Presentation Date and Time
October 22, 2019 (Tuesday) 5:00

Track / Room
Track 2 / Room 304

Authors (Click on name to view author profile)

  1. Lettinga, M. Pavlik (KU Leuven, Physics and Astronomy)
  2. Lang, Christian (KU Leuven, Physics and Astronomy)
  3. Clasen, Christian (KU Leuven, Department of Chemical Engineering)
  4. Dhont, Jan k. (Forschungszentrum Jülich, ICS3)
  5. Hendricks, Jan (KU Leuven, Department of Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
M. Pavlik Lettinga1, Christian Lang1, Christian Clasen2, Jan k. Dhont3, and Jan Hendricks2
1Physics and Astronomy, KU Leuven, Leuven, Flanders, Belgium; 2Department of Chemical Engineering, KU Leuven, Leuven, Belgium; 3ICS3, Forschungszentrum Jülich, Jülich, Germany

Speaker / Presenter 
Lettinga, M. Pavlik

Text of Abstract
High-aspect-ratio colloidal rods are becoming increasingly important in a wide range of technological applications and products. In biology they constitute the frame of the cytoskeleton, in the form of F-actin and micro-tubular networks, while amyloids are responsible for e.g. Alzheimer disease. The mechanical response of complex fluids containing rod-like colloids is hugely affected by the particle dimensions and flexibility, though a direct relation has not been identified so far. The key to a bottom up understanding is to identify the role of rod morphology on the microscopic structural response to flow, underlying the macroscopic mechanical response. Here, we use a library of monodisperse bio-engineered viruses with variable length and stiffness, for which we determine the exact relation between structural and mechanical response by a combination of rheology and Small Angle Neutron Scattering, resolving the orientational ordering of rod-like viruses in the flow-gradient and the flow-vorticity plane [1]. This approach allowed us to quantitatively determine the length dependence of the zero-shear viscosity and shear thinning behavior, using a revised version of the theory developed by Doi, Edwards, and Kuzuu to rationalize the flow behavior. Furthermore, we identified the effect of flexibility, which diminishes viscosity at low shear rates and enhances it at high shear rates. The elongational viscosity of stiff rods obeys theoretical predictions, while it diminishes with flexibility [2]. Thus, this work establishes a fundament for understanding the non-linear flow behavior of more complex rod-like systems. This is demonstrated for mixtures of rods with different length, representing ideal bi-disperse systems, for which we can predict the zero shear viscosity and shear thinning for varying the stoichiometry of the mixture.