Study of optical and electrical properties of thin films of the conducting comb-like graft copolymer of polymethylsiloxane with poly(3-hexyltiophene) and poly(ethylene) glycol side chains for low temperature NO₂ sensing

This work presents an investigation on graft comb copolymer of polymethylsiloxane (PMS) with poly(3-hexyltiophene) (P3HT) and poly(ethylene) glycol as functional side groups. This segmented copolymer was investigated as a NO₂ gas sensing material. Gas sensing, optical and electrical properties of thin films of graft polymers and clean P3HTs (regioregular and regiorandom) are tested and compared. The thin films of investigated materials obtained by spin coating method on interdigital transducers and surface plasmon resonance (SPR) sensor structure are characterized by using atomic force microscopy method and Raman spectroscopy. High changes of resistance and SPR signal caused by action of NO₂ in the concentration of ppm range were observed. It showed that such graft polymers are promising materials for resistance and optical gas sensors operating at low temperatures. Obtained results showed that resistance and sensitivity of graft polymers depend on the content of P3HT and PMS backbone chain length. An optical SPR NO₂ gas sensor and resistance NO₂ sensor based on graft polymer thin films display a very fast response time and a fast regeneration time at low temperature (50 °C) in a dry gaseous environment. Resistance sensor investigation showed that the sensitivity of graft polymers to 5 ppm of NO₂ can be about 20 times higher than in the case of clean P3HTs.