Chin. Phys. B Vol. 19, No. 8 (2010) 088105 Electrical resistance response of polyaniline films to water, ethanol, and nitric acid solution * Yin Hong-Xing(尹红星), Li Meng-Meng(李蒙蒙), Yang He(杨 贺), Long Yun-Ze(龙云泽) † , and Sun Xin(孙 欣) ‡ College of Physics Science, Qingdao University, Qingdao 266071, China (Received 3 November 2009; revised manuscript received 22 January 2010) This paper reports on electrical resistance vs. aging time for the response of polyaniline films under exposure to water, ethanol and nitric acid (HNO 3 ) solution. Camphor sulfonic acid-doped polyaniline films were prepared by a “doping-dedoping-redoping” method, the morphology and microstructures of the films were characterized by a scanning electron microscope and an x-ray diffractometer, the electrical resistance was measured by a four-probe method. It was found that a lower amount of water molecules infiltrating the film can decrease the film’s resistance possibly due to an enhancement of charge carrier transfer between polyaniline chains, whereas excessive water molecules can swell inter-chain distances and result in a quick increase of resistance. The resistance of the film under exposure to ethanol increases and becomes much larger than the original value. However, HNO 3 solution can decrease the film’s resistance sharply possibly owing to doping effect of protonic acid. These results can help to understand the conduction mechanism in polyaniline films, and also indicate that the films have potential application in chemical sensors. Keywords: polyaniline films, conducting polymers, conductivity PACC: 8120S, 7280L 1. Introduction Conducting polymers such as doped polyacety- lene, polyaniline (PANI), polypyrrole and polythio- phene have drawn much attention due to their ex- cellent physical and chemical properties and have been studied extensively in fundamental and ap- plied researches. [1−10] Among these conducting poly- mers, PANI has caught much attention by its diversi- form configuration, [11] good stability, [12] unique mech- anism of doping and extensive prospect of technical applications. [13−15] By now, the electrical resistance response of PANI to different vapours such as moisture, methanol vapour and ethanol vapour has been studied. [16−24] Kahol et al. [21] reported that the existence of water molecules in PANI can reduce the boundary region between the “metallic islands” (where polymer chains are much ordered), thereby enhancing the conductiv- ity of PANI. Tan et al. [17−19] found that methanol or water vapour can result in an increase in conductivity of emeraldine salt and the interaction between vapour and PANI was completely reversible. According to Pinto et al., [22] the resistivity of metallic PANI film was shown to depend very sensitively on the pres- ence of moisture. Tarachiwin et al. [23] also found that the specific conductivity of PANI films responded with positive increments upon exposure to water and ethanol, and the similar result was obtained by Zhou et al. [24] who explored the interaction between PANI nanotube pellets and water/ethanol molecules. Due to the sensibility to vapours and reversibility of inter- actions with vapours, PANI films, pellets, nanostruc- tures and composites have been studied as promis- ing candidates for gas/chemical sensors in recent years. [25−30] However, the concentration of vapour or moisture in most published papers is usually not very high. In order to explore the influence of excessive liquid or solution on the conductivity of PANI films, in this paper, we studied the resistance changes of camphor sulfonic acid (CSA)-doped PANI films under expo- sure to excessive water, ethanol and nitric acid so- lution. Compared with PANI films doped with other protonic acids such as HCl, PANI–CSA film shows a relatively high electrical conductivity at room tem- perature (∼ 200 S/cm), and its temperature depen- dence of conductivity has been reported in previous publications. [22,31,32] * Project supported by the Program for New Century Excellent Talents in University of China (Grant No. NCET-07-0472) and the National Natural Science Foundation of China (Grant Nos. 10604038 and 10910101081). † Corresponding author. E-mail: yunze.long@163.com ‡ E-mail: qdwlxsx@163.com c ⃝ 2010 Chinese Physical Society and IOP Publishing Ltd http://www.iop.org/journals/cpb http://cpb.iphy.ac.cn 088105-1