The rheology of multiwalled carbon nanotube and carbon black suspensions

Abstract

This paper is concerned with a direct experimental and modeling comparison of the rheology of carbon black (CB) and multiwalled carbon nanotube (CNT) suspensions within a Newtonian epoxy matrix. Experimental observations of the effect of shear on CB and CNT microstructure are reported for a range of CB and CNT suspension concentrations. Steady shear, time dependent shear behavior, and oscillatory linear viscoelasticity (LVE) of the suspensions are reported and remarkably strong similarities were observed between the CB and CNT suspension rheology, for example, 4 wt. % CB and 0.4 wt. % CNT suspensions. Optical observations showed that both the CB and CNT microstructures were shear rate sensitive and a structure-dependent hybrid Maxwell-Voigt phenomenological model with a yield stress was developed that gave a reasonable fit to the rheological data. The structure model parameters for both systems were found to be of a similar order of magnitude, although the onset of rheology development for the two systems occurred with a decade difference of concentration. The experimental rheological results and model fit indicated that for both CB and CNT suspensions, the observed rheology changes were dominantly controlled by aggregate size and interaction, rather than the respective particulate and filament morphology of the CB and CNT microstructures. The critical concentration for the onset of rheology development was, however, dependant on the basic morphology of the CB and CNT suspensions. V

Characterization of carbon nanotube dispersion and filler network formation in melted polyol for nanocomposite materials

“…For a more comprehensive evaluation of the state of CNT dispersion and its relationship with filler network quality, rheological measurements can be used with the caveat that rheological properties are also dependent on CNT concentration, polymer-CNT interactions, filler aspect ratio and flow history. [20,42,43] The dependence of magnitude of complex viscosity (η*) on the oscillatory frequency (ω) is shown in Fig.6-a. The control sample shows Newtonian behavior in a wide range of frequencies due to the low molecular weight of PTMEG.…”

“…[18] However, the occurrence of different microstructures at different length scales may result in contradictory interpretation of the data for CNT-polymer nanocomposites. [20] A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 4 The objectives of this work are to evaluate the state of CNT dispersion at different length scales and to provide quantitative measures of dispersion and filler network quality. Moreover, to the best of our knowledge, this is the first comprehensive and systematic study on the direct dispersion of CNT in a melted semi-crystalline media using ultrasonication without the aid of solvents.…”

Simultaneous Rheoelectric Measurements of Strongly Conductive Complex Fluids

“…Carbon black (CB) which refers generically to colloidal soot particles produced from the incomplete combustion of fossil fuels, is utilized extensively in a wide variety of industrial applications including batteries, paints, coatings as well as filled rubbers and tires. CB serves as an additive to convey protection from ultraviolet light, increase toughness, improve processability and to enhance electrical conductivity [60,61]. Composed of permanently fused "primary" particles whose diameter is about 30 nm [62], CB particles are of typical size 200-500 nm and display short range attractive interactions of typical strength 30 k B T [63].…”

“…Recent studies have shown that the mechanical properties of weak attractive gels can be tuned by controlling their shear history [61,66,68]: abrupt flow cessation or "quenching" leads to highly elastic gels, whereas slow cessation of shear leads to weak solids characterized by a vanishingly small yield stress for decreasing flow cessation rate. In this subsection, we investigate the evolution of the electrical properties concomitantly to the elastic properties of the gel prepared by flow cessation experiments at various cessation rates.…”

Electrically conductive adhesives with a focus on adhesives that contain carbon nanotubes

“…Some researchers have studied the dynamic viscoelastic behavior of these dispersions in the linear regime and have shown that a physical network is formed, giving rise to the so‐called rheological percolation 74, 75. The nonlinear viscosity of CNT dispersions in epoxy prepolymers in continuous flows has also been scarcely treated 61, 74, 76, 77. The results indicate that under continuous shear flow, the physical network is destroyed, giving rise to a viscoplastic and shear thinning behavior, which is reflected in the viscosity data of Figure 3.…”