Wireless sensor network based wearable smart shirt for ubiquitous health and activity monitoring

Nanofibers of a composite of a silicon-containing polyelectrolyte, polyethylene oxide and polyaniline (PANI) were obtained by electrospinning and heat treatment. The morphologies of the composite nanofibers were characterized by scanning electron microscopy, which showed that the nanofibers with a diameter of 250–500 nm formed a non-woven mat with highly porous structure. It was found that the polymer composite nanofibers showed impedance change from 6.3 × 10⁶ to 2.5 × 10⁴ Ω with the increment of relative humidity (RH) from 22 to 97% at room temperature, exhibiting high sensitivity and good linearity on a semi-logarithmic scale. In addition, they exhibited fast and highly reversible response characterized by very small hysteresis of 2% RH and short response time (t_90%: 7 s and 19 s for adsorption and desorption between 33 and 97%RH, respectively). The modification of the electrode with poly(diallyldimethylammonium chloride) prior to the deposition of nanofibers improved their humidity response, which may be related to the enhanced contact between the nanofibers and underlying substrate. The effect of PANI on the humidity response of the composite nanofibers was also investigated, and it was found that PANI effectively decreased the impedance of the nanofibers. The electrospun polymer composite nanofibers may find applications in the preparation of high performance humidity sensors.