Surface modification of multi-walled carbon nanotubes by a sol–gel reaction to increase their compatibility with PMMA resin

The dispersion and the thermal characteristics of surface-modified MWNTs introduced into PMMA resin were investigated. The surface was modified by the chemical syntheses of a series of siloxane-containing compounds using acid-treated MWNTs through a sol–gel reaction. The acid-treatment was performed by ultrasonicating the pristine MWNTs in an HNO3/H2SO4 solution. These new materials were characterized by FTIR, zeta potential measurement and SEM. The sol–gel products were negatively charged and could be easily dispersed in toluene and THF solvent. The surface-modified MWNT/PMMA composites were generated by ultrasonicating and the mechanical stirring of the sol–gel products with the PMMA resin. The dispersion effect was maximized by incorporating octyltriethoxysilane to acid-treated MWNT in the PMMA resin. The thermal stabilities of the MWNT-containing PMMA resins were determined by DSC and TGA. The Tg values decreased as the content of the surface-modified MWNT increased, but the Td values were rose drastically from 207.7 to 271.7 °C. The marked improvements in thermal properties were attributed to the well dispersion of MWNTs that were bonded with organosilane chains on the surface.