The Gas Sensing Behavior Of Uniaxially Aligned Nanofiber Yarns By Electrospinning

A gas sensor is a device which can detect the presence of different gases in an area, especially those gases which might be harmful to humans or animals. It is well-known that the sensitivity of chemical gas sensors is strongly affected by the specific surface of sensing materials. A higher specific surface of the sensing material can lead to the higher sensor sensitivity. With the development of science and technology, nanotechnology has attracted a great deal of attention in the past few decades.Therefore many nanotechniques have been employed to manufacture the sensing materials, taking advantage of the large specific surface of nanostructured materials.Electrospinning has been recognized as an efficient and simple technique for the fabrication of nano-sized fibers from a polymer solution or melt in terms of its versatility, flexibility and ease of fiber production. However, most of these nanofibers have been manufactured in randomly oriented and isotropic nonwoven mats. Although this random configuration is acceptable for sensors, it’s desirable to obtain oriented and assembled structure including well-aligned nanofiber sheets, bundles or yarns for sensors. In this study, we investigate a processing method for effectively fabricating uniaxially aligned fiber yarns consisting of thousands of coaxial conducting polymers(PPy or PANI) and polyacrylonitrile(PAN) or Polyacrylonitrile/Single-Walled Carbon Nanotube(PAN/SWCNTs) composite nanofibers using a modified electrospinning method and in situ solution polymerization process. These uniaxially aligned composite nanofiber yarns were transferred to an interdigitated electrode to construct a gas sensor. To pursue its potential applications, its electrical responses towards ammonia(NH3) vapor were measured at room temperature, which also has leading importance to study and application of nanoyarns on gas sensors.First of all, we make uniaxially aligned polyacrylonitrile(PAN) nanofibers yarns by a modified electrospinning method.Then we synthesis polypyrrole(PPy) or polyaniline(PANI) on the surface of PAN nanoyarns to form uniaxially aligned and coaxial PAN/PPy and PAN/PANI nanoyarns. The morphology、structure and composition of composite nanoyarns were were tested by SEM、FETEM、TEM and FTIR, and electrical conductivity and mechanical properties were also tested. We successfully synthesized uniaxially aligned PAN/PPy and PAN/PANI with coaxia structure(PAN nanofibers yarns as the core layer and PPy or PANI as core layer) and th mechanical and electrical properties of PAN nanoyarns were significantly improved.Secondly, we made the gas sensor by fixing the coaxial PAN/PPy nanoyarn on the interdigita electrode and then tested its sensor performance. The coaxial PAN/PPy nanoyarn sensor responsed and recovered quickly, had good reversibility,repeatability as well as high selectivity with th concentration of 250-2000 ppm of ammonia. And we tested the sensitivity of coaxial PAN/PP nanoyarn sensor with different concentrations of doped acid(TSA), and it showed that when th mole of the TSA was 0.2 mmol, the composite nanoyarn sensor performed the highest sensitivit of 2.5 with the concentration of 2000 ppm.Thirdly, we made the PAN/PANI composite nanoyarn sensor by fixing the PAN/PAN composite nanoyarn on the interdigital electrode,and tested its sensor performance with th concentration from 20-2000 ppm of ammonia.It shows that the PAN/PANI composite nanoyar sensor responsed and recovered quickly,had repeatability by testing its sensitivity with the sam50 ppm for five times,and showed good selectivity by testing its sensitivity in different gases o ammonia,dichloromethane, ethanol as well as acetone,respectively.At last,we tested its sensivit of PAN/PANI composite nanoyarn with different doped acids,it showed that the sulfosalicylic aci(SSA) doped PAN/PANI- SSA performed the highest sensitivity.Finally, we added different SWCNTs into the solution of PAN in order to modify the propert of PAN nanoyarn and make PAN/SWCNTs composite nanoyarns with 5wt%(SWCNTs), 10wt%15wt%, respectively. The morphology, molecular structure and crystal structure of SWCNTs /PAN composite nanofiber yarns were tested by SEM、TEM、FTIR and XRD.The effects of SWCNT with different concentrations on mechanical properties of SWCNTs /PAN composite nanofibe yarns were also investigated. It was found that SWCNTs /PAN composite nanofiber yarns showe great morphology and were uniaxially aligned. The tensile strength of the PAN/SWCNT composite nanofiber yarn reached 24. 25 Mpa, when the concentration of the SWCNTs was 5 wt%Then we made the PAN/SWCNTs/PANI-SSA gas sensor by synthetizing PANI doped with SSA o the surface of 5wt% PAN/SWCNTs nanoyarn, and it showed that the PAN/SWCNTs/PANI-SSA gas sensor showed higher sensitivity than PAN/PANI-SSA with the same condition.