A resistive-type sensor based on flexible multi-walled carbon nanotubes and polyacrylic acid composite films

•We developed a sensitive humidity sensor using multi-wall carbon nanotubes.•The 33 wt% multi-wall carbon nanotube film was highly flexible.•The sensor was sensitive over a wide humidity range.

A humidity sensor film was fabricated by loading high numbers of multi-wall carbon nanotubes (MWCNTs) in a poly(acrylic acid) (PAA) polymer matrix containing poly(4-styrenesulfonic acid) (PSS) to enhance the MWCNT dispersion. Cross-section images demonstrate that the MWCNTs distribute evenly throughout the matrix. The fabrication processes and sensing mechanisms of the film are explained to investigate the flexible properties and humidity-sensing characteristics of the film. The film loaded with 33 wt% MWCNTs is much more flexible than an overhead projector (OHP) film and shows similar electrical resistance to pure CNT Bucky paper. The sensor film composed of 1:2 MWCNTs:PAA is highly sensitive to humidity (0.069/%RH) and displays good linearity (0.99).