Polyaniline/poly(ε-caprolactone) composite electrospun nanofiber-based gas sensors: optimization of sensing properties by dopants and doping concentration.

Electrospinning was utilized to synthesize a polyaniline (PANI)/poly(ε-caprolactone) (PCL) composite in the form of nanofibers to examine its gas sensing performance. Electrical conductivity of the composite nanofibers was tailored by secondary doping with protonic acids including hydrochloride (HCl) or camphorsulfonic acid (HCSA). FT-IR and diffuse reflectance UV-vis spectroscopy were utilized to examine doping-dependent changes in the chemical structure and the protonation state of the nanofibers, respectively. The oxidation and protonation state of the composite nanofibers were shown to strongly depend on the doping agent and duration, demonstrating a simple way of controlling the electrical conductivity of the composite. PANI/PCL electrospun nanofibers having various electrical conductivities via varying dopants and doping concentrations, were configured to chemiresistors for sensing various analytes, including water vapor, NH3, and NO2. Secondary doping with Cl(-) and CSA differentially affected sensing behaviors by having distinctive optimal sensitivities. Biphasic sensitivity with respect to electrical conductivity was observed, demonstrating a facile method to enhance gas sensitivity by optimizing secondary doping. A balance between Debye length of the nanofibers and overall charge conduction may play an important role for modulating such an optimal sensitivity.