Tensile strain dependent donductivity of flexible single-wall carbon nanotube network

Abstract

Deformation of the lattice structure of single-wall carbon nanotubes (SWCNT) has been known to change its conductivity by changing the band structure. Especially, external strain induced 1% elongation of a semiconducting carbon nanotube lattice has been shown to increase the band gap as much as 10 %. Here, we investigate the external strain dependent conductivity of a SWCNT network formed on a stretchable silicone elastomer surface for possible mechanical deformation sensor application. The SWCNTs were dispersed in 0.1% sodium dodecylbenzene sulfonate (NaDDBS) solution under ultrasonic agitation. SWCNT network thin-film was initially formed, using vacuum filtration, on ~20 nm pore alumina membrane filter. To transfer the SWCNT bundle thin-film onto a flexible substrate, poly-dimethylsiloxane (PDMS) was cured directly on the filter. After filter removal, a highly flexible SWCNT thin-film was formed on the PDMS surface. We measured the change in SWCNT network conductivity depending on the sample elongation. For 50 % strain applied to the PDMS, a conductivity change of ~10 % was observed. Since the vacuum filtration process produces nanotube networks with random orientation the net strain applied to the nanotubes reduces from the local strain on the PDMS by a factor of cos2θ, where θ is the orientation of the nanotube relative to the strain direction . Also, since the surface of the nanotubes have been functionalized to become hydrophilic, the hydrophobic PDMS surface strain will not all be translated to the nanotube strain. We will also present strain dependent conductivity results on samples with different nanotube densities. The mechanical coupling strengths of different layers of nanotubes on the PDMS surface will result in a graded response to applied external strain.