Mechanical and swelling properties of polyacrylamide/polyacrylic acid composite hydrogels: The effects of network structure and carbon nanotube reinforcement

The tensile elastic modulus and swelling ratio of polyacrylamide/polyacrylic acid hydrogels were investigated to evaluate the effects of gel structure (random copolymer and interpenetrating network) and reinforcement with multi-walled carbon nanotubes (MWCNT) on their mechanical properties. The tensile modulus of the interpenetrating network gels was significantly higher than those of the random copolymer gels when compared under the same swelling ratio. This difference can be explained by the difference in stiffness between their respective component crosslinked polymers. The tensile modulus of both hydrogels increased by reinforcement with MWCNT, while the maximum swelling ratios decreased. Alteration of the mechanical and swelling properties by reinforcement with MWCNT could be explained by spatial distribution of hydrogen bonds among MWCNT, acrylamide, and acrylic acid moieties.