Air stability of n-type single-walled carbon nanotube films with anionic surfactants investigated using molecular dynamics

Abstract

The semiconducting property and air-stability of n-type single-walled carbon nanotube (SWCNT) are important for manufacturing all-carbon thermoelectric generators. We fabricated n-type SWCNT films with different anionic surfactants via drop-casting followed by heat treatment. Among the surfactants used (sodium dodecyl sulfate (SDS), sodium cholate (SC), and sodium dodecylbenzene sulfonate (SDBS)), the SWCNT films with SDBS surfactants exhibited an n-type Seebeck coefficient for 35 days. Structural analyses of the films showed that the SWCNT bundles and SDBS surfactants were homogeneously mixed. To investigate the mechanism behind the air-stability of the n-type property in SWCNT films, molecular dynamics (MD) calculations were performed. The MD calculations revealed that the adsorbability of SDBS molecules to SWCNT was higher than that of the other surfactants, which was consistent with the results of structural analyses. The sodium atoms in the vicinity of the SWCNT surface were vital in imparting n-type properties to the SWCNT. The SWCNT films with SDBS surfactants exhibited n-type properties for a long period of time because the surfactant molecules homogeneously covered the SWCNT surface, which enhanced the transfer of electrons from the sodium atoms to the SWCNT. The findings will aid toward further improving the air-stability of n-type SWCNT films using new surfactants.