A Comparative Study on Humidity Sensing Performances of Polyaniline and Polypyrrole Nanostructures

Abstract

This paper addresses the preparation of polyaniline (PAni) and polypyrrole (PPy) nanostructures as humidity sensor elements. The semicrystalline microstructure and chemical structure of synthesized PAni and PPy were studied by X-ray diffraction and Fourier transform infrared spectroscopy, respectively. The morphology of these polymers was studied by scanning electron microscopy and transmission electron microscopy, indicating fibrillar and tubular nanostructures for PAni and PPy, respectively. The humidity sensing performances of sensors based on the prepared nanostructural PAni and PPy were investigated, and the sensing mechanisms of both systems have been discussed. The interesting reverse behaviors during humidity exposure of PAni-and PPy-based sensors in different water vapor concentrations have been comprehensively justified. The temperature dependency of the electrical conductivity for PAni and PPy samples was investigated. The UV-vis spectroscopy was used to study the effect of moisture on the electronic transport properties of PAni and PPy nanostructures. C Experimental MATERIALSThe aniline and pyrrole monomers, hydrochloric acid (HCl), ethanol, ammonium persulphate (APS, (NH 4 ) 2 S 2 O 8 ), and anhydrous iron (III) chloride (FeCl 3 ) were all purchased

Nanostructured Polypyrrole-Based Ammonia and Volatile Organic Compound Sensors

“…The researchers usually distinguish among three different template methods, namely hard-template synthesis, soft-template synthesis [53,63,64], and reactive template synthesis [65]. One of the most used hard templates is nanoporous anodic alumina oxide (AAO) which provided uniform dimension of pores, high density, high aspect ratio and controllable diameter of nanostructures.…”

“…Some works focused on the relative humidity sensing are briefly presented in the following paragraphs. Joulazadeh et al studied the humidity sensing performances for the previously described PPy nanostructures synthesized via anhydrous FeCl 3 and methyl orange [64]. The tubular morphology of PPy nanostructures showed positive changes of the resistance (R > R 0 ) for a low humidity concentration (25 ppm of water vapour), and negative changes (R < R 0 ) for higher concentrations (56 ppm of water vapour).…”

Designing polymeric sensing materials: what are we doing wrong?

“…Polymer swelling can affect the response in different ways. For example, when water absorbs into PANI, swelling increases the resistance (reduces the conductivity); however, when water absorbs into polypyrrole (PPy), swelling reduces the resistance (increases the conductivity) …”

“…However, when too much water is absorbed, the water molecules push the polymer chains further apart, resulting in the polymer swelling, and reducing the amount of conjugation between polymer chains. This means that it is more difficult for a charge to be carried across multiple polymer chains, thus resulting in a decrease in PANI's conductivity …”

Coaxial conducting polymer nanotubes: polypyrrole nanotubes coated with polyaniline or poly(p-phenylenediamine) and products of their carbonisation

“…There was no obvious point to blending the two polymers. Accordingly, virtually all papers on PANI or PPy have dealt with these polymers separately; even a comparison of the properties of the polymers has only rarely been reported Blinova et al, 2007;Omastová et al, 2010;Joulazadeh et al, 2014;Liu et al, 2014). One-dimensional objects, such as nanotubes or nanofibres, are of particular interest because the charge transport in such materials might be enhanced compared with the globular morphology.…”