Study of Polyaniline for Use in an Organic Field Effect Transistor

Polyaniline's emeraldine base form was synthesized via chemical polymerization in HCl acidic media utilizing ammonium persulfate as the oxidant. Synthesis was done at room temperature and -30 'C and characterized for differences by X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. Methanol soxhlet extraction was done to increase number average molecular weight from 77,400 to 81,000 and decrease the poly dispersity index from 3.82 to 2.14. Films were cast using N, N'- Dimethylpropyleneurea and N-Methylpyrrolidone and showed poor mechanical properties upon acidic doping. Cyclic voltammetry was done with HC1 as the acidic media and an ITO coated slide as the working electrode. The resulting films proved difficult to handle due to the thin nature of the film and tendency to crack when left on the glass substrate. Due to difficulties associated with films formed via cyclic voltammetry and casting, an additional method was explored. An in situ polymerization was done in the presence of polyethylene terephthalate fiber to thinly coat emeraldine salt onto the surface. This thin coat was not detectable by HATR FTIR but preliminary Rutherford backscattering indicates a film thickness of 70 nm to 110 nm in some samples. Electrical conductivity was measured by a four point probe and concentric surface probe technique. Resistances of one synthesis were approximately103 Ω/sq while those samples of a different synthesis showed a much greater surface resistance approaching insulator levels. Scanning electron microscopy was used to examine the conductive surface of the coated fibers. Mechanical characteristics were compared using dynamic mechanical analysis and showed a minor (8.5% — 11%) increase in the fiber's stiffness with the added coating. The coated PET fiber in situ polymerization technique was determined to be the best approach in comparison to film casting and electro chemical polymerization for the development of organic field effect transistors. It was superior in its ease of manufacturing, application needs, and time utilized to create a smooth film on a flexible substrate. Future work was suggested for the continued improvement and development of the project.