They can complement the disadvantages of pure inorganic and organic materials. It is also observed that hybrid materials have smaller grain size and better gas-sensing stability in air [19,20]. Geng  reported that the polyaniline/SnO2 hybrids exhibited good sensitivity to volatile organic compounds. Ram et al.  synthesized poly(ethylenedioxythiophene) (PEDOT)/SnO2 composite thin films, and studied their gas sensitivity to NO2. These hybrid materials-based gas sensors exhibited much higher sensitivity than that of the pure inorganic and organic materials-based gas sensors.However, the adherence between the sensing layer and the substrate is then of outmost importance. The ceramic substrate-based sensors usually need to use an inorganic binder to promote the adhesion between the components .
For flexible organic substrates, elevated temperatures should be avoided and generally polymeric sensitive materials with intrinsic binding properties are necessary.PDDAC is frequently used as a binder in the electrodeposition of iron oxide films, which enables the formation of thick metal oxide films, preventing cracking of the film and increasing the adhesion between the sensitive film and the substrates . It can also be used to adjust the electrostatic force between flexible fibers and inorganic filler particles, thus facilitating the retention of fillers . Moreover, considering that PDDAC is a charged polyelectrolyte, the electrostatic interaction between PDDAC and metal oxide may modify the sensing properties of the mental oxide at room temperature.
In this paper, we have investigated a novel flexible ethanol sensor based on SnO2 doped polydiallyldimethylammonium chloride (PDDAC), in which PDDAC acted as both the binder and the dopant. The sensor has a detection limit of 10 ppm and shows good selectivity to ethanol. Furthermore, the sensing mechanism is also discussed in detail.2.?Experimental2.1. Materials PreparationSnO2 (AR, purity �� 99%) and PDDAC (M.W. = 100,000?200,000 g/mol) were purchased from Tianjin Wind Ship Co. Inc., Tianjin, China. They were used as received without any treatment. All de-ionized water (DIW) used had a resistance above 18 M��/cm. The PI substrate (Upilex-125S, UBE, Japan) was washed with acetone, ethanol, and DIW, respectively.2.2. Carfilzomib Fabrication of Gas SensorInterdigitated gold electrodes were formed on the flexible PI substrate (10 mm �� 11 mm) by E-beam evaporation of a thin (5 nm) layer of Cr, serving as the adhesion layer and then a 50 nm Au layer. The electrodes have four pairs of interdigital fingers, each of 4,950 ��m length and 50 ��m width and the gap between the electrodes is also 50 ��m. The solution of PDDAC was formed by dissolving 2.5 g PDDAC in 25 mL DIW at 298 K. Then 2.