Soft Matter Seminar: How rods give structure to fluids and how structure is distorted by flow

Pavlik Lettinga, Forschungszentrum Jülich GmbH, Institute of Complex Systems

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]. Finally, I will show how long semi-flexible F-actin filaments order in shear flow, using in situ confocal microscopy. Here, theoretical input is still missing to explain this extreme non-linear response [4].

1. M. P. Lettinga and E. Grelet. Self-Diffusion of Rodlike Viruses through Smectic Layers. Phy. Rev. Lett. (2007) Vol. 99, 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) 17800
3.  C. Lang, L. Porcar, J. Kohlbrecher, M.P. Lettinga, The Connection between Biaxial Orientation and Shear Thinning for Quasi-Ideal Rods. Polymers, 8 (2016) 291.
Kirchenbuechler, I., D. Guu, N. A. Kurniawan, G. H. Koenderink, M. P. Lettinga. Direct visualization of flow-induced conformational transitions of single actin filaments in entangled solutions. Nature Communications, (2014) Vol. 5, 5060.


Monday, September 17, 2018 at 11:00am to 12:00pm

Regents Hall, 351
3700 O St. NW

Event Type

Academic Events


Students, Faculty/Staff


Georgetown College, Institute for Soft Matter Synthesis and Metrology, Physics




Pavlik Lettinga, Forschungszentrum Jülich GmbH, Institute of Complex Systems

Event Contact Name

Peter Olmsted

Event Contact Email

Google Calendar iCal Outlook