Effect of water release on thermal properties of polyaniline
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Conducting polyaniline (PANI) was studied by thermal expansion measurement, thermogravimetric analysis and by electrical conductivity measurement. Relative elongation and coefficient of thermal expansion (CTE) were determined from room temperature to 60 °C. Various temperature profiles were used. During heating, the treatment of samples at a constant temperature higher than the room temperature, or evacuation, water was released from the samples. Water release was detected by mass and thermogravimetric analysis. Water release was connected with shrinkage of the PANI samples and apparent negative CTE in the first thermal cycle. In the following thermal cycles, it increased and reached a positive value. CTE of PANI attained values in the range of −30 × 10−6 K−1 up to 20 × 10−6 K−1 in dependence on water content in the sample before measurement and on experimental conditions of measurement. Irreversible shrinkage of the polymer was the largest in the first thermal cycle. Water release exhibited a strong time and temperature dependence, and it was only partially reversible. The electrical conductivity was measured by a four-point van der Pauw method. Relative electrical conductivity decreased with amounts of water release. Relative decrease of electrical conductivity reached as far as 20% after evacuation 7 h at the room temperature.
KeywordsPolyaniline Water-born polymer Thermal expansion Electrical conduction TG analysis
Experiments have been performed in the Magnetism and Low Temperature Laboratories (http://mltl.eu/) within the program of the Czech Research Infrastructures (LM 2011025). The financial support of the Czech Science Foundation (13-00270S, P108/11/1298) is also gratefully acknowledged.
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