Influence of the pH on the Surface and Optical Properties of the Thin Film of Polyaniline / Polyethylene Terephthalate C
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Influence of the pH on the Surface and Optical Properties of the Thin Film of Polyaniline / Polyethylene Terephthalate Composite. The AFM and Spectroscopies Studies. Rafaella T. Paschoalin1,2 ,Clarice Steffens1,2, Alexandra Manzoli1, Mhbuti R. Hlophe3, Paulo S. P. Herrmann1,2 1 National Nanotechnology Laboratory for Agribusiness (LNNA), Embrapa Agricultural Instrumentation, P. O. Box 741, 13560-970, São Carlos, SP, Brazil 2 Biotechnology Graduate Program-UFSCar, São Paulo, Brazil 3 North West University, Mafikeng Campus, South Africa ABSTRACT The effect of pH was investigated on the morphological and spectroscopic properties of PANI thin films on PET. PANI/PET strips were prepared by a patternprinting technique and coated with a thin film of polyaniline in situ emeraldine oxidation state, doped with HCl (PANI-HCl), obtained by in situ polymerization. AFM, UV-VIS-NIR and FTIR/ATR spectroscopic results showed that pH has a great influence on the polymer layer morphology of the coating layers, while the intensity of vibrational bands decreases with rising pH, increase due to changes in the H-bonded structure in the polymer chain. Keywords: Polyaniline, in situ polymerization, roughness, and conductivity. 1. INTRODUCTION In the last few years, the interest in the development of new sensors for use in industry, agriculture, environment, medicine and other areas, has increased significantly. Among conducting polymers, polyaniline (PANI) has been studied more than any other, owing to its easy chemical synthesis and high environmental stability. PANI has electrical and optical properties suitable for use in optical sensors for monitoring pH [1], since its electronic absorption band sensitive to changes in pH is very broad, and optical sensors using PANI as the active layer are suitable for pH measurements in the range of 2 to 12 [2]. Given the advantages of low cost and short response time, pH optical sensors based on PANI thin film as the sensitive layer represent an interesting alternative to other sensors [3]. This paper reports the characterization of a low-cost optical sensor material assessing the influence of pH on a PANI film coated on PET. A printing technique was used to manufacture the coated
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pattern. PET (polyethylene terephthalate) and PANI thin film in the emeraldine oxidation state, deposited by in situ polymerization, were used as substrate and sensitive layer, respectively [4]. The morphology and roughness of the films were analyzed by atomic force microscopy (AFM). The degree of doping of the PANI was investigated by UV-VIS-NIR and FTIR/ATR spectrophotometry. 2. EXPERIMENTAL 2.1. Materials Aniline (Aldrich) was purified by distillation. Ammonium persulfate ((NH4)2S2O8), Sodium hydroxide (NaOH) and hydrochloric acid (HCl) were used as received (Merck). Water was purified to18 M:*cm-1 resistivity by the Milli-Q system (Millipore Inc.). The substrate PET (polyethylene terephthalate) was purchased from Nashua (XF-20, Nashua-USA). 2.2. Stripes The stripes were developed by a pattern-printing technique [4,
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