Monodisperse SiC/vinyl ester nanocomposites: Dispersant formulation, synthesis, and characterization
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H. Thomas Hahna) Department of Materials Science and Engineering, University of California—Los Angeles, Los Angeles, California 90095; and Department of Mechanical and Aerospace Engineering, University of California—Los Angeles, Los Angeles, California 90095 (Received 30 November 2008; accepted 6 January 2009)
A novel dispersant “mono-2-(methacryloyloxy)ethyl succinate” was formulated for dispersing 30-nm SiC nanoparticles in vinyl ester resin. The eight carbon rule was used as the guideline to achieve a particle–particle separation of 20 to 60 nm for colloid stability. Fourier transform infrared spectroscopy was performed to characterize the SiC particle surfaces. Only a negligible amount of oxidized layer was observed; which illustrates that the SiC surface is basic. Thus, the Lewis base-Lewis acid reactions make the functional group –COOH an effective adsorbate to the SiC nanoparticle surface. The organofunctional group “methacrylates,” which exhibits the best wet strength with polyester copolymerizes with styrene monomers in the vinyl ester during cure. Hence, this novel dispersant also acts as an efficient coupling agent that reacts with both SiC and vinyl ester. The monolayer coverage dosage of 62 fractional wt% of the dispersant was used to attain the minimum filled resin viscosity. The multicomponent compositional imaging using atomic force microscopy confirmed the monodisperse SiC nanoparticles in vinyl ester. The 3 vol% SiC reinforced vinyl ester achieved a 75% increase in modulus, 42% increase in strength, and 75% increase in toughness as compared with the neat resin without nanofiller reinforcement. I. INTRODUCTION
Polymer nanocomposites are hybrid structures where one phase has at least one dimension in the nano-size range (usually defined as 1–100 nm). Compared to particles with sizes in the micrometer range, nanoparticles have a large surface area, and consequently, a nanocomposite may exhibit special properties arising from phase interactions at interfaces.1 However, the degree of enhancement of a particular property is highly dependent on the filler/matrix material system used, the filler/ matrix interfacial bonding, and the state of dispersion of the filler throughout the matrix.2,3 A good dispersion of nanofiller in the polymer matrix coupling with a strong interface between the two phases is essential to achieve enhanced mechanical properties.4,5 Covalent ceramic materials like silicon carbide (SiC) have been recognized as potential candidates for structural applications because of their superior mechanical properties (strength, stiffness, and hardness), chemical a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0176 J. Mater. Res., Vol. 24, No. 4, Apr 2009
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inertness (oxidation and corrosion resistance), and thermal stability at high temperatures. The low viscosity, coupled with rapid curing rate at room temperature and the relatively low cost of vinyl ester resins, has led to their extensive u
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