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


Suspensions and Colloids

Transient behavior of carbon nanotube suspensions in an epoxy

October 20, 2009 (Tuesday) 4:25

Track 1 / Lecture Hall

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  1. Khalkhal, Fatemeh (École Polytechnique de Montréal, Chemical Engineering Department)
  2. Carreau, Pierre J. (Ecole Polytechnique, CREPEC, Chem. Eng. Dept.)

(in printed abstract book)
Fatemeh Khalkhal and Pierre J. Carreau
CREPEC, Chem. Eng. Dept., Ecole Polytechnique, Montreal, Quebec H3C3A7, Canada

Khalkhal, Fatemeh

Carbon nanotubes (CNTs) have found a lot of applications in different industries recently. They are mainly used to enhance the electrical, mechanical and thermal properties of polymers. The rheology of CNT suspensions has been the subject of interest by many researchers recently, but very little can be found on the transient behavior of these suspensions. To better understand the evolution of the microstructure of CNT suspensions under flow the transient behavior of CNT suspensions in an epoxy was studied in the semi-dilute and concentrated regimes. The effect of rest time between two consecutive start-up tests in clockwise and counter clockwise directions was analyzed in order to monitor the structure recovery of the suspensions. Similar to other filled polymeric systems, stress overshoots were observed in the forward flow. If no rest time was given between two consecutive experiments, no overshoot was observed in reverse flow; however by increasing the rest time between two consecutive start-ups, stress overshoots appeared in reverse flow and their extent increased by the rest time. It was observed that most of the structure recovery occurs shortly after cessation of flow in time scales expected from the Brownian time scales. In the semi-dilute regime, the suspension structure was recovered at small applied shear rates in the reverse direction after sufficient rest time. However, at higher shear rates, the structure recovery was limited even after long rest times. In concentrated regime, the structure was totally recovered after cessation of flow after 1 h rest time. The complete structure recovery at high concentrations could be due to the tight arrangement of CNTs in the suspensions and formation of entangled nanotube networks that stores the stress work and reforms a similar structure to the initial one after cessation of flow.