Effect of viscosity and surface tension on dynamic percolation in liquid media

Abstract

ABSTRACTPercolation of carbon nanotubes in liquid media has been studied as a function of their surface tension and intrinsic viscosity. Carbon nanotubes were dispersed in different liquids by means of ultrasound, and the suspensions were gradually further diluted to obtain a large number of well‐defined filler contents. Percolation was probed with a remarkable accuracy thanks to a specific test procedure combining dilutions and electrical testing. Percolation threshold values were found to be lower (close to 0.01 vol %) than the ones obtained in molten polymers, due to the ease of particles aggregating in liquid media. The aggregation over time of carbon nanotubes from a dispersed and distributed state into particle networks was also monitored. Best known as dynamic percolation, this resulted in a percolation threshold eventually reduced by a factor of two. We then show that decreasing the matrix viscosity increases the dynamic component of the percolation process, yielding decreased critical filler fraction and percolation time (0.002 vol %). Finally, the effect of the difference in surface tension between the filler and matrix was also quantified. Large differences favor the aggregation mechanisms and thereby reduce the percolation threshold. An analytical model is finally proposed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46313.