Rheology of high-aspect-ratio nanocarbons dispersed in a low-viscosity fluid

Abstract

Printing inks typically consist of a functional component dispersed within a low-viscosity resin/solvent system where interparticle interactions would be expected to play a significant role in dispersion, especially for the high-aspect-ratio nanocarbons such as the graphite nanoplatelets (GNPs). Rheology has been suggested as a method for assessing the dispersion of carbon nanomaterials in a fluid. The effects of phase volume of ammonia plasma-functionalized GNPs on a near-Newtonian low-viscosity thermoplastic polyurethane (TPU) resin system have been studied using shear and quiescent oscillatory rheology. At low concentrations, the GNPs were well dispersed with a similar shear profile and viscoelastic behavior to the unfilled TPU resin, as viscous behavior prevailed indicating the absence of any long-range order within the fluid. Particle interactions increased rapidly as the phase volume tended toward maximum packing fraction, producing rapid increases in the relative viscosity, increased low shear rate shear thinning, and the elastic response becoming increasingly frequency independent. The nanoscale dimensions and high-aspect-ratio GNPs occupied a large volume within the flow, while small interparticle distances caused rapid increases in the particle-particle interactions to form flocculates that pack less effectively. Established rheological models were fitted to the experimental data to model the effect of high-aspect-ratio nanocarbon on the viscosity of a low-viscosity system. Using the intrinsic viscosity and the maximum packing fraction as fitting parameters, the Krieger-Dougherty (K-D) model provided the best fit with values. There was good agreement between the estimates of aspect ratio from the SEM images and the predictions of the aspect ratio from the rheological models. The fitting of the K-D model to measured viscosities at various phase volumes could be an effective method in characterizing the shape and dispersion of high-aspect-ratio nanocarbons.

The Effect of Carbon Ink Rheology on Ink Separation Mechanisms in Screen-Printing

“…This is likely due to a reduction in particle to particle interactions associated with the reductions in relative volume of carbon particles in the solvent-resin matrix, enabling particles to align more readily with the flow. As well as this, there would be less hydrodynamic disturbance in the flow field as there are fewer particles for it to be diverted around [32]. All dilutions also showed relatively little hysteresis over the shear rates assessed, when shear was reduced back down to 1 from 100 s -1 , suggesting the ink would take little time to recover to its initial viscosity after flow during printing.…”

“…Screen-printing inks have a vast range of rheological profiles, depending on the particle morphologies, interactions between particles, particle size distribution as well as solvents and resins used [9][10][11][12]29,30]. Work by Holder et al [31] and Claypole et al [32] have identified rheological methods for optimising the formulation of screen-printing inks containing high volumes of functional materials, covering a wide range of ink viscosities and viscoelastic characteristics which can be quantifiably related to the quality of the print produced. Therefore, changing the rheological profile of the ink should also create quantifiable changes in the ink separation stages which could be related to the print quality and performance.…”

“…Dilution of the ink led to reductions in elastic modulus (G') at all measured frequencies. As with viscosity, this is associated with fewer particle to polymer and particle to particle interactions which are able to elastically store energy [32,35,36]. Viscous modulus (G'') also reduced with dilution.…”

The influence of carbon morphologies and concentrations on the rheology and electrical performance of screen-printed carbon pastes

“…More carbon should lead to a more conductive ink, but excessive carbon concentrations could lead to agglomerations of particles and increased surface roughness, exceeding a certain carbon conductor mass fraction could lead to print defects (such as mesh marking) which impinge upon the electrical performance of the ink [10,22]. Different filler (carbon) concentrations also alter the rheological profile of the ink, which can be quantifiably related to the quality of the print produced [23,24]. High speed imaging techniques have been used by Xu and Willenbacher [25] and the authors [26] to identify how the rheological profiles of screen printing inks influence the inks deposition and separation mechanism during screen printing.…”

Economical conductive graphite‐filled polymer composites via adjustable segregated structures: Construction, low percolation threshold, and positive temperature coefficient effect

“…31 Igor Krupa et al reported that the elastomers (styrene-isoprene styrene block copolymer) with graphite fillers provided with the low percolation threshold of about 2.2 vol% and excellent tensile properties. 32 In this paper, in order to obtain economical highperformance PTC materials, the conductive segregated system, where UHMWPE was selected as the separation phase and thermoplastic urethane (TPU) including graphite fillers was used as the continuous phase due to the characteristics of low melting point, strong fluidity, and low fluid low fluid viscosity of TPU 33 and excellent properties of high toughness, wear resistance and low friction and the eliminating of the NTC effect of UHMWPE, 29,[34][35][36] would be constructed by the combination of mechanical crushing and melt blending method. The effect of the controlled microstructure on the electrically conductive properties and PTC effect was investigated in detail.…”