Novel Gas Sensing Nanocomposites And Devices

Gas sensing materials and devices are important to industry security, manufacture monitoring, domestic safety, medical aid and military detection. The current gas sensing materials and devices are not able to satisfy the need of people and the appearance of new materials and the advance in technology provides new choice and possibility. It is essential to fabricate gas sensing materials and devices which can realize room temperature measurement and have long usage period. In this dissertation, the intrinsic gas sensing mechanism and recent research hot-spots have been combined and transparent, hierarchical network structure gas sensing film and self-healing gas sensing film have been developed. The following is the content in detail and the achieved results:Silver nanowire network structure has been used as template to in situ polymerize polyaniline, with ammonium persulfate oxidizing aniline to polymerize in the process. The balance of etching effect and the polymerization of aniline makes it possible to obtain transparent, hierarchical polyaniline network. As silver nanowires have functioned as template on the PET, the structure of template-synthesized polyaniline differs significantly from the polyaniline synthesized by non-template method. The polyaniline synthesized by silver nanowire template is hierarchical network structure and the polyaniline synthesized by non-template method is particle-like structure. The gas sensing performance of the two kind of films also have a lot differences, with the hierarchical network structured polyaniline exhibiting higher gas sensing sensitivity and better selectivity than non-template polyaniline. The gas sensing sensitivity of the hierarchical network structured polyaniline film to 50 ppm ammonia is 11.5 times of the particle-like polyaniline film and the detection limit of the hierarchical network structured transparent polyaniline film to ammonia can be as low as 5 ppm. The hierarchical network structured polyaniline film can be developed to gas sensors by silver paint attachment, making the process of fabricating gas sensors more easy. The hierarchical network structured polyaniline film has shown better gas sensing performance than the polyaniline device fabricated by ceramic tube method and has generally maintained the resistance after 100 flat-bending cycles. This work provides some insight into wearable equipment and transparent electronic devices.Multiwalled carbon nanotubes have assembled on the top surface micrometer-thick PAA/PEI film. The polyelectrolyte has stacked one layer by another through electrostatic interaction and the difference of the optical property and the flexibility is investigated for the polyelectrolyte films of different stacking cycles. Three different coating methods have been adopted to prepare carbon nanotube films, including drop coating by dropper pipette, spray coating by spray bottle and Meyer-rod coating. The homogeneity and transparency of the CNT films fabricated by different method have been investigated. The multiwalled carbon nanotubes coated micrometer-thick PAA/PEI film have shown outstanding homogeneity and transparency. The multiwalled carbon nanotubes coated micrometer-thick PAA/PEI film prepared by 2.5 mg/mL of MWCNT dispersion exhibited 74% transparency at 550 nm. Furthermore, the self-healing property of the micrometer-thick PAA/PEI films and the multiwalled carbon nanotubes coated micrometer-thick PAA /PEI films has been investigated. The gas sensing performance of the multiwalled carbon nanotubes coated micrometer-thick PAA/PEI films has been tested. This work provides some insight into self-healing electronic devices.