Electrical and mechanical properties of high electrical conductivity CNT/Cu-yarns with Br doping and Cu encapsulation

Carbon nanotubes (CNTs) are an ideal starting material for the development of strong, light-weight conductors. In this work, we pursued the development of high specific electrical conductivity and high specific strength CNT/metal composites. We started with CNT yarns which had an initial electrical conductivity, sigma(e), of 3.14 MS m(-1) and a density of 1.32 g cm(-3). We brominated the yarns, demonstrating increases in sigma(e), with our best samples reaching sigma(e) = 7.00 MS m(-1). To increase the stability of the bromination, we electroplated a Cu layer onto the Br-doped yarn which led to a stabilization of the conductivity improvement. This was quantified by monitoring periodically the sigma(e) of a Br-doped and metallized CNT yarn over a period of 69 days, during which time the sample was otherwise exposed to ambient conditions. Analysis gives a value 6.15 MS m(-1) for the brominated yarn after metallization which is excellent for CNT yarns. Tensile tests on these Cu/CNT composites showed tensile strengths reaching 700 MPa, Young's modulus values of 22.8 GPa, and specific tensile strength values of 146 kN*m kg(-1) (this latter is 6X that of Cu). Our best CNT-Cu composites show specific conductivity values comparable with that of Cu but with much higher specific tensile strengths.