Study of the Molecular Interactions between Functionalized Carbon Nanotubes and Chitosan

Molecular dynamics (MD) simulations were performed to calculate the interaction between chitosan at different degrees of deacetylation (DD) and carbon nanotubes (CNTs) functionalized with either amine (-NH2) or carboxylic ( COOH) groups. The objective was to elucidate the effect of the CNT functionalization type and the different DD of chitosan on the mechanical properties of the nanocomposite. For a certain DD, where the glucosamine and acetyl-glucosamine units are uniformly distributed along the chitosan chain, MD simulations showed that this molecule depicts a large contacting superficial area that allows the interaction with the functionalized CNT. It was also found that the attractive interaction between a 50% DD chitosan and the -NH2 functionalized CNT (CNT-NH2) was the strongest among the different deacetylated cases under study. For the 50% DD case, a wrapping effect of the CS chain around the CNT-NH2 structure was displayed which was attributed to hydrogen bonds formation between the amine groups in the CNT and the -OH and -NH2 groups in the chitosan molecule. Composite films of chitosan, reinforced with multiwall carbon nanotubes (MWCNT) functionalized with either -NH2 (MWCNT-NH2) or -COOH (MWCNT-COOH), were prepared to measure their Young's module. The experiments showed that the films reinforced with MWCNT-NH2 exhibited larger Young's modules than those functionalized with -COOH groups. The above was due, likely, to the strong interaction between the amino functionalized CNTs and the polymeric matrix. The simulation results were in agreement with the experimental data.