SoR logo The Society of Rheology 81st Annual Meeting
October 18-22, 2009 - Madison, Wisconsin
View Paper Info and Abstract


Suspensions and Colloids

Rheo-microscopy of semi-flexible fiber suspensions in shear flow

October 22, 2009 (Thursday) 10:35

Track 1 / Lecture Hall

(Click on name to view author profile)

  1. Keshtkar, Mehdi (École Polytechnique, CREPEC - Chemical Eng.)
  2. Heuzey, Marie-Claude (École Polytechnique, CREPEC - Chemical Eng.)
  3. Carreau, Pierre J. (Ecole Polytechnique, CREPEC, Chem. Eng. Dept.)
  4. Rajabian, Mahmoud (École Polytechnique, CREPEC - Chemical Eng.)
  5. Dubois, Charles (École Polytechnique, CREPEC - Chemical Eng.)

(in printed abstract book)
Mehdi Keshtkar, Marie-Claude Heuzey, Pierre J. Carreau, Mahmoud Rajabian, and Charles Dubois
CREPEC - Chemical Eng., École Polytechnique, Montreal, QC, Canada

Heuzey, Marie-Claude

The rheological behavior of fibers with different flexibilities suspended in a silicone oil in the semi-concentrated regime has been investigated by rotational rheometry and flow visualization. The microstructure evolution of the suspensions has been observed at different shear rates using two techniques: a Linkam Optical Shearing System (CSS450) and using a continuously-focusable InfiniVar® microscope placed under the lower plate of a rheometer, which has been replaced by a glass plate. Results from these two techniques show how the size of the visualization window and the number of fibers visualized influence the calculation of the second-order orientation tensor that is used to quantify the orientation state of the fibers. As expected it was observed that applying shear forces aligned fibers in the flow direction. However the extent of alignment was a function of shear rate, applied strain and fiber flexibility. The results showed that by increasing fiber flexibility, the orientation in the flow direction decreased. Rigid fibers oriented themselves more rapidly in the flow direction and the degree of orientation was higher than for flexible fibers. The second-order orientation tensor was represented graphically by ellipses to facilitate the observation of its evolution. Finally, a GENERIC model (General Equation for Non-equilibrium Reversible-Irreversible Coupling) has been used to predict the rheological behavior of the semi-flexible fiber suspensions as well as their microstructure. The model takes into account fiber-fiber interactions and also the semi-flexible nature of the fibers. The graphical representation of the second-order orientation tensor was confronted with model predictions and it was in good qualitative agreement.