Pressure Dependent Conductivity of Strained Carbon Nanotube Networks on Elastomer Substrates

Abstract

Recently, there has been growing interest in utilizing the strain dependent conducting properties of highly transparent and mechanically flexible carbon nanotube networks (NTNs) for various mechanical strain sensor applications. All of the reported devices utilize the strain dependent collective reduction in the electrical conductivity of the carbon nanotube network, which results mainly from the reduction of inter-nanotube conduction paths and partly from individual nanotube lattice deformation. Here, we report on the tactile pressure dependent conductivity of compressively strained single-walled NTNs fabricated on poly-dimethylsilaxane (PDMS) substrates, which showed an increase in conduction with pressure. The compressively strained NTNs were fabricated by releasing the pressure built in the pre-stretched PDMS substrates, as they come in contact with the NTNs for contact transfer to the PDMS surface. The nanotubes behaved collectively to the applied local compressive strain and resulted in the buckling of the NTN creating locally periodic undulations. The variation in undulation period and amplitude through out the NTN surface depended on the local nanotube density and contact area with the PDMS substrate surface. The change in NTN conductivity depended on the strength of the applied vertical pressure and with 0.2 Mpa applied vertical pressure, the NTN sheet conductance increased rapidly by 10 %. We applied cyclic pressures (0.2 MPa) at 15 second intervals and found that the tactile pressure dependence was reproducible for several hundred cycles. The tactile pressure sensitive conductivity may be due to the buckled undulations in the NTN being planerized and the nanotube interconnections within the NTN increasing resulting in an increase in conduction. We will report on the detailed fabrication process of the strained NTN on PDMS and their nanoscale deformation induced tactile pressure sensing operation. This work was supported by the Korea Science and Engineering Foundation(KOSEF) grant funded by the Korean government(MOST) (No.R01-2007-000-10898-0)