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Room temperature sensing characteristics of the polypyrrole (PPy) films modified with different weight percentages of ZnO nanowires (ZnO-NWs) have been studied for various oxidizing (NO2 and Cl2) as well as reducing (H2S, NH3, CH4, and CO) gases. We demonstrate that ZnO-NW (50 wt %):PPy composite films are highly selective to Cl2 along with high-sensitivity (40 at 10 ppm), fast-response (55 s), and highly reproducible response curves. It has been shown that negatively charged O2− surfaces of ZnO-NW transfer electrons to PPy, making it in a highly reduced form. A strong localization of charge carriers in the reduced PPy makes composite film highly resistive (>1010 Ω cm) as well insensitive to interaction with most of the gases except Cl2. Cl2 being highly oxidizing gas interacts with composite films and causes a sharp reduction in its resistivity.

A study was conducted to ascertain the effect of variation in spin speed and baking temperature on β-phase content in the spin-coated poly(vinylidene fluoride) (PVDF) thick films (∼4−25 μm). Development of β-phase is dependent on film stretching and crystallization temperature. Therefore, to study the development of β-phase in films, stretching is achieved by spinning and crystallization temperature is adjusted by means of baking. PVDF films are characterized using Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy. It is observed that crystallization temperature lower than 60 • C and increase in spin speed increases the β-phase content in PVDF films. Crystallization temperature above 60 • C reduces β-phase content and increases α-phase content. It was also observed that viscosity of the PVDF solution affects the β-phase development in films at a particular spin speed.

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