Preparation of carbon nanotube/PMMA nanocomposite in supercritical carbon dioxide

Nanocomposites of well dispersed single wall carbon nanotube (SWNT) in polymer matrix are expected to have improved electric, thermal, and mechanical properties. The extent of dispersion and the adhesive interactions between the nanotubes and polymer are important criteria for a successful process. A novel method to prepare SWNT/polymer nanocomposite by in-situ polymerization in supercritical carbon dioxide (scCO ₂) is presented in the study. The surfaces of SWNTs are first functionalized with amino ethyl methacrylate (AEMA) and then copolymerize with methyl methacrylate (MMA) via in-situ polymerization in supercritical CO ₂. The supercritical solvent featuring controllable liquid-like density, reduced viscosity, and enhanced diffusivity facilitates the transport of monomers into the entanglement area or interstitial space in SWNT bundles. In-situ polymerization enhances dispersion of SWNTs; tethered PMMA chains on the nanotube surface increase the chemical affinity with the polymer matrix. FTIR shows clear evidence of surface coupling of the nanotubes and tethered PMMA. Electron microscopy analysis from SEM and TEM reveal a much enhanced dispersion of nanotube bundles in polymer matrix and excellent surface coverage of PMMA on SWNTs even after several washes with organic solvents. Surface functionalization with AEMA is found to be critical to the success of fabricating the nanocomposites. The success of functionalization of SWNT followed by polymerization using this method can be generalized to other polymeric systems.