Rheological Properties of Nanocomposite Aqueous Dispersions Based on Poly(acrylamide-co-acrylic acid) and Carbon Nanotube

Carbon nanotubes (CNTs) are a new class of nanomaterials that have gained special attention due to their unique properties such as excellent electrical and mechanical properties. Nanocomposite hydrogels, a novel category of hydrogels, have received great attention both in industry and scientific research because of their exceptional structural and mechanical properties. A nanocomposite aqueous dispersion based on poly(acrylamide-co-acrylic acid) and modified carbon nanotube was synthesized through in situ radical polymerization. Water can be a good candidate instead of toxic organic solvents for preparation of poly(AA-co-AM)/CNT nanocomposite aqueous dispersions. The rheological properties of the nanocomposites were significantly improved compared to those of pure copolymer samples. Modification of carbon nanotubes by acid was conducted to introduce hydroxyl and carboxyl groups on their surface in order to achieve a better dispersion behavior and suitable interactions between the nanoparticles and polymer matrix. Once the oxidation step was finished, amide functional groups were inserted into the CNT particles through amidation reaction. The surface modification reactions of CNT were tracked by FTIR and Raman spectroscopy techniques. FTIR and Raman spectra were utilized in order to investigate the dispersion behavior of nanoparticles and to confirm the formation of linkages between the nanoparticles and polymer matrix, respectively. In addition, the rheological features including viscoelastic behavior of samples, the sol-gel transition phenomenon, dynamic oscillatory frequency sweep and steady shear measurements were studied. Finally, the relationship between the improved rheological properties (modulus and viscosity) and the dispersion microstructures caused by dispersion of nanoparticles, formation of networks and interfacial interactions between Poly(AA-co-AM) macromolecular chains and CNT nanoparticles were determined.