Intrinsic conductive polymer for renewable energy applications
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The conjugated polymers provide us promising characteristics which make them good candidates for electronic devices such as supercapacitors and polymer solar cells.
Polyaniline is one of the most promising polymers for the unique electrochemical properties, easy preparation and environmental stability. However, polyaniline has been found to be insoluble in organic solvents, which limits its use in the electronic device applications. The molecular interaction between the polymers is the main reason that causes the poor solubility. In order to understand the effect of molecular structure modification, a series of polyaniline was synthesized modifying the polymer backbone and changing the counter anion. For the modified backbone, fluorine and sulfonic group have been introduced to the backbone of polyaniline using hydrochloric acid as a dopant which was observed to improve the solubility. Poly(2-fluoroaniline) was found to be soluble in organic solvents including tetrahydrofuran (THF), dimethylsulfoxide (DMSO), dimethylforamide (DMF) and chloroform. For the counter anion modification, a broad range of dopants were selected from small dopants to highly bulk dopants. For the small dopants, hydrochloric acid and hydrofluoric acids were used for modifying the molecular attraction between the polymer molecules. Extensive study of pH impact on the polymer solubility was conducted using a wide range of pH conditions from 1 to 13, for which alkaline solution was observed to increase the solubility.
Increasing the intermolecular space between the chains by introducing a bulky counter anion will help loosen the tight stacking between the molecules which lead to improve the solubility. p-toluene sulfonic acid and dodecyl benzene sulfonic acid have been used as a dopant to synthesize polyaniline. Dodecyl benzene sulfonic acid doped polyaniline was observed to improve not only the solubility but also the electric conductivity.
Film coating process was applied on several substrates including glass plates and flexible substrate, applying a broad coating techniques covering Doctor blade coating, drop casting and dip coating. The effect of solution secondary doping has been investigated in depth, testing dodecyl benzene sulfonic acid doped polyaniline along with several secondary dopants including m-cresol, p-toluene sulfonic acid and thymol. The doping method proved to reduce the surface resistant from 6 MΩ/□󠅔 to 1 KΩ/□󠅔 with p-toluene sulfonic acid.
A secondary film doping using m-cresol, thymol and p-toluene sulfonic acid was observed to increase the electrical conductivity dramatically and to reduce the surface resistance, for which the surface resistance was observed to be changed from 6 MΩ/□󠅔 to 650 Ω/□󠅔 when p-toluene sulfonic acid was used. In order to elucidate the properties of the polymers, several instruments have been used.