Virtual Seminar"How rods give structure to fluids and how structure is distorted by flow" Pavlik Lettinga


Monday, January 18, 2021 - 16:00




Micro/Bio/Nanofluidics (Shen) Unit would like to invite you to the virtual seminar by Prof. Pavlik Lettinga on January 18 (Monday).
Date: Monday, January 18, 2021 (Monday)
Time: 16:00-17:00
**Zoom session

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Meeting ID: 935 0765 4163
Passcode: 003318


Pavlik Lettinga
Assistant Professor
Forschungszentrum Jülich GmbH


How rods give structure to fluids and how structure is distorted by flow


The most effective way to structure a fluid is by immersing slender rods, as rods have a huge excluded volume. In equilibrium, this leads to an entropy-driven cascade of phase transitions with increasing concentration of rods. When subjecting isotropic, randomly oriented, rods to flow, this leads to a strong shear thinning as volume becomes available by flow aligning the rods. While the first phenomenon is a hall mark for self-assembly, the second phenomenon is of special interest to understand industrial and biological processes industrial applications.
Both subjects will be addressed in this talk, using biological engineered rod-like viruses, with different well-defined length and stiffness. First, I will discuss video microscopy experiments on highly ordered rods, revealing very unusual dynamics that challenge fundamental notions on diffusion [1,2]. Second, I will show how  the geometry and stiffness of rods play a key role in the rheological response, using a combination of Rheology and Small Angle Neutron Scattering (Rheo-SANS), resolving the orientational ordering of rodlike viruses in all relevant directions.  Interpretation of this data for the different model rods on the basis of microscopic theory gives a full understanding of the non-linear flow behavior [3], though the understanding of extensional flow is still challenging [4].

Figure 1 Left: Guest-host system exhibiting a smectic organization as shown by the overlay of a differential interference contrast (DIC) microscopy image, evidencing smectic layers, and of a fluorescence image, displaying the dual labeling of the host and guest particles. The scale bar represents 2.0 μm.  Right: Schematic representation of the guest-host system in both smectic-A and smectic-B phases

1.    M. P. Lettinga and E. Grelet. Self-Diffusion of Rodlike Viruses through Smectic Layers. PRL 99 (2007)  197802.
2.    L. Alvarez, M. P. Lettinga, E.Grelet, Fast Diffusion of Long Guest Rods in a Lamellar Phase of Short Host Particles. PRL 118 (2017) 178002.
3.    Lang, C. et al. Microstructural Understanding of the Length- and Stiffness-Dependent Shear Thinning in Semidilute Colloidal Rods. Macromolecules 52 (2019) 9604-9612.
4.    Lang, C. et al. Effects of particle stiffness on the extensional rheology of model rod-like nanoparticle suspensions. Soft Matter 15 (2019) 833-841.


Prof. Amy Shen

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