Optical microstructure and viscosity enhancement for an epoxy resin matrix containing multiwall carbon nanotubes

Abstract

This paper describes rheological measurements and associated optical microstructural observations of multiwall carbon nanotubes ͑MWCNTs͒ suspended in an epoxy resin matrix. The base epoxy resin was found to be essentially Newtonian, and the progressive incorporation of nanotubes enhanced the low shear rate viscosity of the suspension by nearly two decades. At higher shear rates, the suspension viscosity asymptotically thinned to the viscosity of the matrix alone. The low shear rate viscosity enhancement was correlated with the optical observations of interconnected aggregates of carbon nanotubes, which themselves were induced by the low shear conditions. Intermediate shear rates resulted in a reduction in the size of the aggregates. High shear rates appeared to cause near-complete dispersal of the aggregates. From these results it is conjectured that for this suspension, shear thinning is connected with the breaking of the interconnected networks between nanotubes and or aggregates of nanotubes, and not by nanotube alignment.

Low viscosity processing using hybrid CNT-coated silica particles to form electrically conductive epoxy resin composites

“…In contrast, the two NC suspensions containing discrete, nongrafted CNT exhibit viscosities that are between 1 and 2 orders of magnitude higher at 10 -1 s -1 and which decrease sharply as the shear rate increases. Similar large increases in viscosity at low shear rates resulting from CNT addition have been observed for suspensions in other epoxy resins [18][19][20][21] and water [22], and are attributed to the formation of a percolated network between the CNTs. As the shear rate was increased to > 200 s -1 , the viscosities of the NC suspensions decrease and approach those of the epoxy and the SG6_3 suspensions; behaviour indicative of the break-up of the CNT network [18,20].…”

“…Similar large increases in viscosity at low shear rates resulting from CNT addition have been observed for suspensions in other epoxy resins [18][19][20][21] and water [22], and are attributed to the formation of a percolated network between the CNTs. As the shear rate was increased to > 200 s -1 , the viscosities of the NC suspensions decrease and approach those of the epoxy and the SG6_3 suspensions; behaviour indicative of the break-up of the CNT network [18,20]. The shear viscosity versus shear stress flow curves in Figure 3b show the epoxy resin and the SG6_3 suspensions to display stable Newtonian behaviour over more than three decades of stress (until τ = 3 kPa).…”

A review and analysis of electrical percolation in carbon nanotube polymer composites

“…In columns 6 and 7 dispersion method and solvent in the case of solution processing are specified. Finally, electrical characteristics like percolation threshold Φ C , critical exponent t and maximum observed conductivity σ max are listed in columns [8][9][10]. All percolation thresholds and filler concentrations are given in weight% (wt%).…”

Modelling percolation in fibre and sphere mixtures: Routes to more efficient network formation

“…The simplest case of a binary mixture fibre-sphere was examined using a mixture of fibres with aspect ratio λ = l/d = 20 and spheres of diameter d. Both the fibres and spheres interact with each other by soft-core repulsive forces along with the dissipative and random forces, as described by equations (1) to (3). The initial configuration consisted of uniaxially aligned array of pure fibres which was allowed to relax to find the percolation threshold for randomly oriented fibres.…”

“…The formation of extended networks of particles dispersed in a fluid gives rise to a discontinuous change in the rheological [1][2][3][4][5] and electrical [6][7][8][9] properties of the dispersion at concentrations around the so-called percolation threshold. Historically, percolation theory was first used by Flory [10] to explain the phenomenon of gelation in thermosetting polymers.…”