Structural Stability of Transparent Conducting Films Assembled From Single-Wall Carbon Nanotubes Purified by Electronic Type

Strain-induced structural changes in thin polymer-supported membranes of purified single-wall carbon nanotubes (SWCNTs) are evaluated through the wrinkling instabilities that develop under uniaxial and isotropic compression. Nanotubes that have been separated by electronic type using density-gradient ultracentrifugation are assembled as surfactant-free films on prestrained polydimethylsiloxane (PDMS) substrates, and the strain response is measured using a broad range of techniques. The small-strain behavior is inferred from kinetic changes in the wrinkling topography during the slow drying of pre-swelled polymer supports. Our measurements reveal a remarkable degree of strain softening that couples strongly to the sheet resistance of the membranes through microscale anisotropy. By depositing comparable films on quartz, we use optical (UV-Vis-NIR) absorption spectroscopy to compute the London dispersion spectra of the purified materials, and from these we compute the attractive part of the van der Waals potential between nanotubes of identical electronic type. We find significant differences in the strength of the contact potential between metallic vs. semiconducting nanotubes, which in turn are evident in the modulus and yield strain of the films. Supported by the NSF through CMMI-0969155.