Effect of amino acid-functionalized multi-walled carbon nanotubes on the properties of dopamine-based poly(amide-imide) composites: An experimental study

In a single-step, rapid microwave-assisted process, multi-walled carbon nanotubes were functionalized by S-valine amino acid. Formation of amino acid on nanotube surface was confirmed by Fourier transform-infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, field emission scanning and transmission electron microscopy techniques. The surface-modified nanotubes showed better chemical stability in common solvents such as N,N-dimethylacetamide. The effects of amino acid functionalization of multiwalled carbon nanotubes on the properties of nanotube/poly(amide-imide) nanocomposites were investigated. The functionalized carbon nanotubes (5–15 wt%) were dispersed homogeneously in the poly(amide-imide) matrix, while the structure of the polymer and the nanotubes structure were stable in the preparation process as revealed by microscopic observations. The properties of nanocomposites were characterized extensively using the aforementioned techniques. The composite films have been prepared by casting a solution of precursor polymer containing S-valine-functionalized carbon nanotubes into a thin film and its tensile properties were examined. The Young’s modulus (elastic modulus) and tensile strength of the composite films were greatly improved by the incorporation of modified nanotubes.