Preparation And Characterization Of Thiophene, Poly 3 - Based Composite Thin Film Gas Sensors

Polythiophenes are an important representative class of conjugated polymers that form some of the most environmentally and thermally stable materials being used as electrical conductors,nonlinear optical devices,polymer LEDs,sensors,solar cells and etc. They have attracted a lot of selling academia and industries'attention because of their wide applications future in modern optoelectronics and micro-electronics field, and they had become a hot topic of materials research in recent years.Polythiophene and its derivatives can be used as gas-sensing materials. Comparing with the inorganic oxides gas-sensing materials, they have significant merits, such as low cost, simple preparation method, working at room temperature and etc. However, researches show that pure polymers have problems that sensitivity and selectivity couldn't meet the needs in our daily life. The appearance of nanocomposites helped us to solve this question. As the nano-dispersed phase has a large surface area and strong interface interactions, nanocomposites have different performance in mechanical, thermal, electrical, magnetic and optical characteristic from the general macro-composite materials. Especially, conducting polymer/inorganic oxides nanocomposites can make up for the shortcomings of signal material, the selectivity, sensitivity and stability can be improved.In this thesis, we contained 2 sections as follows:Firstly,Poly (3-hexylthiophene)-indium dioxide (P3HT/In₂O₃) and P3HT/SnO₂ hybrid materials were prepared by mechanical mixing. Their films were coated On QCMs (Quartz Crystal Microbalances) substrate separately by spin coating by method. The films were characterized by UV-Vis and SEM. UV-Vis Spectrum analyses indicated that polymer and inorganic oxide materials were just physics mixed, the characteristic peaks at about 519nm which are consistent with a reported work. SEM analysis showed that the films were coated very evenly on the substrate without cracks. But the films have some darker particles and the polymer was agglomerated in some places. The sensors were exposed to NO₂ and chlorine-substituted methane (CHmCl4-m, m=1, 2). The result showed that these sensors had an approximate line response. P3HT/ SnO₂ film's performance is much better than P3HT/ In₂O₃ and pure P3HT films. When exposed to NO₂, these films showed a slow response and recovery, the frequency of QCM could not return to its origin frequency.Secondly, P3HT/In₂O₃ and P3HT/SnO₂ were coated on two-port surface acoustic wave (SAW) devices with the same method. According to the character of SAW devices, the films on them were much thinner than that on QCMs, films on SAW devices were coated with dilute solution just once. The parameters of SAW devices were tested by network analyzer. Then, these sensors were exposed to these three gases. As the same with QCM sensors. Response to chloroform was much better than that to dichloromethane. P3HT/SnO₂ films had better performances than P3HT/In₂O₃ films. Compared with the responses to chlorine-substituted methane, responses to alcohols were small. These sensors also showed good responses. However, the restorability was not very good.