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Characterization of dispersion of carbon nanotubes in polymer matrices Laura Peña-Parás1, Hubert Phillips III, and Enrique V. Barrera2 1 Universidad de Monterrey, Ave. Morones Prieto 4500 Pte. C. P., San Pedro Garza García, N. L. 66238, México, [email protected] 2 Rice University, 6100 Main Street, Houston, TX 77098, USA. ABSTRACT Dispersions of carbon nanotube polymer composites were characterized by Raman mapping. Single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs), multi-walled nanotubes (MWNTs), and XD-grade carbon nanotubes (XD-CNTs) were dispersed in a vinyl ester (VE) resin using an ultrasonic probe at a fixed frequency. SWNTs were functionalized with succinic acid peroxide (SAP) to enhance dispersion. Increasing ultrasonication energy was found to improve the distribution of carbon nanotubes (CNTs) and decrease the size of ropes, whereas excessive amounts of energy were found to result in damage. The quality of dispersion was verified through optical microscopy and scanning electron microscopy (SEM). INTRODUCTION Since their discovery in 1991 by Iijima and coworkers [1], CNTs have been studied extensively due their exceptional mechanical, electrical and thermal properties. The full achievement of the reinforcing potential of CNTs in composite materials requires good dispersion in the matrix and efficient interfacial stress transfer. However, the dispersion is affected by van der Waals forces among CNTs and the interactions between CNTs and the dispersion medium [2], [3]. Nanotube dispersion may be achieved by a combination of mechanical and/or chemical methods. Commonly used mechanical methods are: ball milling [4], high shear mixing [5], ultrasonication [6], [7], the use of surfactants [8], [9], and functionalization [10-12]. The use of ultrasonication of CNTs in liquids is widely used to break up CNT aggregates during solution processing techniques [7-9]. This process involves the use of ultrasonic excitation of the mixtures to break up nanotube bundles through acoustic cavitation. Ultrasonication forms microscopic bubbles that expand during the negative pressure and cause energy to be released at the point of implosion, which generates a shearing action. However, this shearing can induce scission of carbon nanotubes near the imploding cavitation bubbles, as explained by Lucas et al. [13]. Therefore, there is a need to understand the factors that optimize sonication efficiency in order to maximize the enhancement of properties of carbon nanotubes in polymer composites. EXPERIMENTAL CNTs used in this study were: SWNTs (from Carbon Nanotechnologies, Inc.), DWNTs (produced by Litmus Nanotechnology; diameter: 2.33 nm; length: 3 μm; 30% SWNTs, 50% DWNTs, 20% MWNTs), MWNTs (provided by Shenzhen Nano-Technologies Port Co., Ltd; diameters: 10-30 nm), and XD CNTs (from Carbon Nanotechnologies, Inc.; lot 3365A; mixture of SWNTs, DWNTs and MWNTs). All CNTs were dispersed in vinyl ester by tip ultrasonication with varying energy rates and sonication times. A Cole-Parmer 750 Watt

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Ultrasonic Proc