Characterization of viscoelastic properties of composite films involving polyaniline and carbon nanotubes

The deposition and properties under electrochemical potential control of composite films of polyaniline and single walled carbon nanotubes were studied using high frequency acoustic wave measurements at quartz crystal resonators. Acoustic admittance spectra were used to provide shear moduli for the growing films as functions of thickness and dopant anion (sulfate, nitrate or perchlorate). The electrochemical and viscoelastic data were compared with those obtained in a parallel set of experiments in the absence of carbon nanotubes. The presence of carbon nanotubes in the deposition solution enhances the rate of polyaniline deposition by a factor of 3–5, according to the dopant. In all media, the shear modulus components increased with film thickness and in any given medium both the storage and the loss moduli were greater in the presence of carbon nanotubes. Since SEM images do not reveal the presence of the carbon nanotubes directly, they are deduced to interact sufficiently strongly with the polymer as to become fully encapsulated. A mean field model is adapted to provide predictive capability at a simplistic level for composite film viscoelastic properties in terms of the mechanical properties of the constituents. When applied to the experimental data, it suggests that the level of carbon nanotube incorporation is modest, despite its significant effect on film deposition and properties.