The ultrasonic dispersion of multiwalled carbon nanotube (MWCNT) suspensions was assessed by studying the differential sedimentation of the particles in an acid anhydride often employed as a curing agent for epoxy resins. The particle size distributions were characterized by the means of a disc centrifuge, and the effect of dispersion time, power density, and total energy input, for both bath and circulation probe ultrasonic dispersing equipment was investigated. The mass of freely suspended MWCNTs relative to agglomerated MWCNTs was estimated as a measure of the quality of the dispersions, and the results showed that this ratio followed a power law scaling with the energy dissipated in the sonication treatment. If the sonication power level was too high, sonochemical degradation of the curing agent could occur. The mean agglomerate MWCNT size distribution was estimated, and the fragmentation of the agglomerates was modeled by means of fragmentation theory. Indications of both rupture and erosion fragmentation processes for the MWCNT agglomerates were observed. 1. Introduction Carbon nanotubes (CNTs) have been studied extensively since the landmark paper by Iijima in 1991 [1]. The exceptional mechanical, thermal, and electrical properties combined with the high aspect ratio and large surface area have made CNTs a promising material for a wide range of applications. However, there are major challenges to overcome in order to utilize these properties. There are several different production methods for CNTs, such as laser ablation, electrolysis, electric arc discharge, sonochemistry, chemical vapour deposition, and catalyst arrays [2]. These methods produce different CNTs with different chemical structure, length, diameter, defects, and varying types and degrees of contamination [3]. This will affect physical properties, such as differences in nanotube curvature, reactivity, failure mechanisms, mechanical properties, and surface interactions. Although the mechanical properties of carbon nanotubes are superior to, for example, continuous and short carbon fibres, problems with dispersion, load transfer, and alignment in a polymer matrix have, so far, not led to CNT composites being a competitive alternative to these more traditional materials. Carbon-fibre-reinforced polymers (CFRPs) are more suitable for use in structural composites. The primary role of a polymer matrix is to hold the fibres in plane and transfer load, but there are modes of deformation where an increase in the mechanical properties of the polymer matrix is of importance. In this context,
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