In this thesis, polyaniline nanofiber based flexible gas sensors have been developed for the detection of toxic environmental gases. Several substrates such as rigid silicon dioxide, polyimide and paper have been fabricated as sensor platforms. Gold interdigitated microelectrodes have been fabricated on silicon dioxide and polyimide substrates by photolithography and e-beam evaporation technique (lift-off process). Polyimide film with 15 micron thickness has been fabricated by spin coating. Simple filter papers have been used and silver and carbon electrodes have been fabricated on the paper by screen printing method. Electrospinning has been used as the principal method of synthesizing the sensing material (polyaniline nanofibers). Polyaniline Emeraldine Base (EB) doped by camphor-sulfonic acid (HCSA) was used as the precursor. Two types of polymeric binders were used, polystyrene (PS) and polyethylene oxide (PEO). The effect of using a secondary solvent, tetrahydrofuran, along with the primary solvent, the chloroform, has been investigated by UV-Visible spectroscopy. The sensors were fabricated by a simple and low-cost procedure. The sensor platforms were directly placed in front of the syringe needle of the electrospinning setup and high quality nanofibers were deposited directly on the interdigitated electrodes that were fabricated on the substrates beforehand. After electrospinning and post-processing, the sensors were taken to the gas sensing test chamber to test their performance in sensing the target gases. The target gases were common toxic environmental gases, hydrogen sulfide ($H_2S$), nitrogen dioxide ($NO_2$) and ace-tone. The sensors have shown good sensitivity, low detection limit and very good recovery time compared with the previously proposed sensors based on PAni. Several characterization techniques have been undertaken to analyze the morphology and properties of the synthesized nanofibers. The electrical resistance of the sensors has been measured by a semiconductor parameter analyzer. Several SEM images were taken from each sample and these images have been used to investigate the effects of processing parameters (such as binder's concentration) and environmental parameters (such as humidity) on the morphology of the nanofibers and their gas sensing performance. Energy Dispersive (EDS) and Fourier Transform Infra-Red (FT-IR) spectra of the nanofibers were taken in order to determine the elements and components existing in the nanofibers web. Several complementary tests have been done to examine the dependence of the performance of the sensor to the environmental humidity and the mechanical robustness and flexibility of the sensors. Stability of the sensor’s response over time has been tested and sensor’s detection limit was determined. Simplicity of the synthesizing method, together with the cheap and flexible substrates provide a low-cost and room temperature gas sensor that is unique in terms of sensitivity, detection limit and recovery time.
본 연구에서는 독성의 환경가스를 감지하기 위하여 폴리아닐린 나노섬유 기반의 가스센서를 개발하였다. 전기방사방식을 이용하여 나노섬유를 합성하였다. 유연한 플랫폼 및 휘어지지 않는 플랫폼을 가스센서 플랫폼으로 쓰기 위해 제작하였다. HCSA 에 의해 도핑 된 EB를 프리커서로 이용하였다. PS, PEO, 두 가지 유형의 폴리머 바인더를 이용하였다. 용매의 종류와 같은 공정 조건과 습도와 같은 환경적인 인자들의 영향이 나노섬유의 형태와 가스측정 성능에 미치는 영향을 연구하였다. 가스 센서는 간단하고 경제성 있는 방법으로 제작되었다. 유연 센서 플랫폼은 종이와 폴리이미드 기판이 이용되었다. 종이 플랫폼에는 스크린프린팅 방법이, 폴리이미드 플랫폼에는 전자빔증창법을 이용하여 각각의 플랫폼에 미소전극을 형성하였다. 센서 플랫폼을 전기방사 장비의 주사기 바늘 바로 앞에 위치시켰으며, 고품질의 나노섬유가 서로 맞물려있는 전극에 곧 바로 형성 된다. 측정하고자 하는 가스는 세 가지의 일반적인 독성 가스로 황화수소, 이산화질소, 일산화탄소이다. 제작된 센서는 과거 연구되었던 PANI 기반의 가스센서와 비교하여 좋은 감도, 낮은 측정한계 그리고 매우 좋은 반응속도를 보인다. 간편한 합성 방법과 값싸고 유연한 기판의 이용으로, 뛰어난 성능의 감도, 측정한계 그리고 빠른 반응시간을 보이는 저 비용이면서 상온에서 작동하는 가스센서를 제작할 수 있었다.
