Preparation Of PANI/PI/PANI Compound Films And Mechanism

As one of the most important conducting polymers, polyaniline (PANI) has many advantages, including structural diversity, unique proton doping mechanism, outstanding stability and good electrical conductivity, which has extensive application prospect in optoelectronic devices. But it also shows a number of shortcomings, such as problem of conductivity stability, problem of function to reproduce and processing difficulties. In this thesis, PANI/PI/PANI compound films with high surface quality and compact structure are prepared through an in-situ growth on polyimide (PI) film matrix in the dispersion polymerization of aniline, which provide a new method to improve the processibility of PANI. The PI matrix has excellent mechanical properties and heat resistance. The films will have potential applications in organic film capacitors.The main topics mentioned in the thesis are about the practical aspect and mechanism of PANI films. Firstly, the task discusses the method to measure conductivity of PANI films and the stability mechanism of polyvinylpyrrolidone (PVP) as stabilizer. Secondly, the ways to improve thickness and conductivity of films are explored. Finally, the mechanism of PANI films forming on PI matrix is studied, in which the film process and driving force are discussed in detail.It indicates that PANI/PI/PANI compound films with high surface quality and PANI layers exhibits a micro/nano scale thickness and high adhesion with PI matrix. It is confirmed that the film forming on PI matrix is composed of proton acid-doped PANI and is free of PVP by UV and IR spectrum analysis. PANI films have good conductivity reached 100¹0¹S·cm^-1, which is close to the conductor's conductivity.PANI films with high quality are related to the use of the polymeric surfactant PVP as the stabilizer and can be prepared with high molecular weight PVP as the stabilizer. However, low molecular weight PVP and small molecular surfactants as stabilizers can not stabilize PANI particles to form good films. The results show that the stabilization of high molecular weight PVP is related to the long-chain molecular structure and special distribution of hydrophilic groups. The mechanism needs further study.Researches show that both aniline's twice putting and extra amount methods are able to increase the thickness of compound films. Modified PI matrix disposed with ultrasonic and various reaction solutions can reduce the hydrophobic of the matrix, while increase the thickness. However, too high hydrophilic is not always conducive to increasing the thickness. Filming-twice technology can substantially increase the thickness of PANI layer on PI matrix which can reach 2000nm. The conductivity of PANI films with different thickness is almost the same order of magnitude, which indicates that the thickness has no direct relationship with conductivity.The main factors affecting the conductivity of PANI films are the oxidation and doping of PANI. The dosage of oxidant can largely affect the conductivity of PANI films. When the dosage of APS is increased, the conductivity of PANI films is firstly increased and then decreased. The conductivity of films is highest when the molar ratio of APS to An is 5:4, up to 4.6×10⁰S·cm^-1. The species of doping acid can also affect the conductivity of PANI films. Compound films with high conductivity can be obtained by adopting hydrochloric acid or p-toluenesulfonic acid.The forming process of PANI films deposited on PI surface takes on three stages. First, constitutional units containing aniline segment, such as the compound of An hydrochloride, An cation free radical, An oligomer, are adsorbed onto PI matrix and then nucleates. Second, the film quickly grows. Third, growth alleviates and film thickness comes to a saturation state. Both the adsorption and the growth happen at the induction period and get through the whole reaction process, affecting film surface quality greatly.PANI film has secondary micro/nano structure. Under the stabilization of PVP, PANI deposited on PI surface firstly generates small particles (a diameter of 20³0nm), then small particles continue to accumulate and generate larger particles (a diameter of 200⁴00nm), until covering the entire surface of PI film. The main driving force of PANI film is the hydrophilic/hydrophobic interaction.