Pacific Institute for the Mathematical Sciences - PIMS

Fibers and fibrils in extension and shear: from fundamental fluid physics to material properties.

The structure (orientation and spatial distribution) of elongated particles is critical in order to control the mechanical properties of biomaterials consisting of elongated particles such as cellulose nanofibrils or fibers.The orientation is often controlled by flow and the first part of the talk describe how extensional flow can be used to prepare filaments from cellulose nanofibrils; our filaments seem to be the world’s strongest biomaterial. However, the fibril alignment is limited by rotational diffusion and the details of the competition between extensional driven alignment and rotational diffusion is investigated utilising Small Angle X-ray Scattering (SAXS) at the synchrotron PETRAIII in Hamburg, Germany.

In the second part of the talk, the behaviour of prolate ellipsoids in shear will be discussed. The rotational behaviour in the complete Reynolds/Stokes state space has been obtained from simulations. It will be shown that the dynamics is dominated by the stability of the so-called log-rolling motion where the ellipsoid is aligned with the vorticity.

Bio: Dr. Fredrik Lundell is an Associate Professor of the Department of Mechanics at KTH Royal Institute of Technology in Stockholm, Sweden. He is also the Director of the Odqvist Laboratory. After the completion of his PhD (2003) in Fluid Mechanics, KTH, and serving as a Postdoctoral associate (2003-04) at Commisariat l’Energie Atomique, Grenoble, France, Lundell joined KTH as Researcher in 2004 before moving up in the ranks to Associate Professor. He works primarily on suspension flows, often related to processing of biomaterials. Fredrik’s work is primarily experimental using methods such as PIV, MRI, synchrotron X-ray radiation and POM. Fredrik is the recipient of many awards, including 2011’s award as ”Teacher of the Year” at KTH.

Location: ESB 2012