In Situ Polymerized Polyaniline Films Under High Pressure

In the past years, the research of polyaniline (PANI) has been a hot special topic. This is because of many benefits of PANI, such as low cost, easier preparation, excellent environmental stability, and higher conductivity etc. Many systemic studies results indicate that the molecular structure, physical and chemical properties of PANI depend on the synthesis method and reaction conditions, intensively.The aim of this work is to explore a new synthesis of PANI, in which a high pressure is applied, and to investigate the effect of high pressure on the properties of PANI. The new method is "In-situ polymerization under high pressure", abbreviated to ISPHP, that created by us firstly. Our experimental results show that the new method is suitable for PANI film. Comparing to those PANI films obtained at ambient pressure, our samples exhibit many interesting characterizations, including nano-network of micro-morphology, lower rough surface, higher conductivity, and higher conjugate degree.In this thesis, we firstly investigate the main properties of PANI films prepared under different high pressure. Between 150 MPa and 600 MPa high-pressure ranges, it is easy to synthesize PANI film with nano-network. In addition, an obvious Red-shift of polaron band in UV-Vis spectra is observed. The Red-shift indicates that the conjugate degree of our samples is increased. The thickness of the films by ISPHP is strongly related to applied pressure. The thickness of PANI films obtained at atmosphere is the lowest (about 45 run), while it increases to -100 nm in the pressure range of 150 - 450 MPa and drops to about 70 nm as applied pressure at 600 MPa. SEM shows that the surface of the films obtained by ISPHP is slicker than those synthesized at ambient pressure.From ambient pressure to 600 MPa, the conductivity of films increases as increasing the pressure. At 600 MPa, the conductivity of film by ISPHP is as high as 16.9 S/cm. One hand, the volume of "Metallic Island" in PANI nano-network is larger than those in granular films according to the metallic island model. On the other hand,high pressure improves the contact between the metallic islands, which is benefit to the hopping of carry charges. Both effects result in a distinct increase in conductivity.We also study the thermal kinetics for ISPHP. In the case of high pressure, the induction period and polymerization of growth of film are largely contracted. Base on the absorption law and chemical thermal kinetics, we conclude that applied high pressure improves the rate of absorption of cation radicals and the reaction rate constant K.Also, a growth model of PANI film for ISPHP is established. Under high pressure, the chains grow easily alone the surface of the substrate than perpendicular direction. This is the main reason why the nano-netwok is formed in ISPHP.In the case of high pressure, there is a relationship between conjugate degree and reaction time. In initial progress, the increase of reaction time results in the overlap of conjugate it bond in the chains of PANI. In later period in synthesis, the interaction between quinone ring and N atom in the PANI chains decreases as reaction time increases further.Finally, we investigate the influence of proton acid as dopant in ISPHP to PANI films. The effect of proton acids on the properties of PANI obtained by both ISPHP and normal method is similar.