Fundamental Research and Applications of Conducting Polyaniline and Oligoanilines
Conjugated polyaniline, as one of the earliest developed conducting polymers, has been extensively studied during the past few decades and applied to gas sensors, mechanical actuators, energy storage devices, electrochromics, gas and water separation membranes, anti-corrosive coatings, etc. However, the long and entangled polymer chain conformations with uncertain numbers of aniline units (i.e. polydispersity) has limited its processability and also covered up some important information regarding the conjugated aniline-based system. Therefore, conjugated aniline oligomers, with defined chain lengths and a specific number of aniline units, are ideal small molecules for deciphering polyaniline. Previous studies have shown that tetraaniline is able to form distinct crystalline morphologies by introducing different acidic dopants and vertically aligned crystals with high electrical conductivities based on the nature of small molecules. These reports not only revealed the interactions between dopants and
tetraaniline molecules, but also provided some insights into self-assembly and charge transport in organic semiconductors.
The goals of this dissertation are to investigate fundamental properties of oligoanilines in order to further our understanding of the conjugated aniline system/derivatives, and to introduce tetraaniline to applications where polyaniline finds processing difficulties that are hard to deal with. Chapter 1 provides an introduction, while Chapter 2 compiles detailed performance data and separation mechanisms of conjugated polymer-based membranes for gas separation, water filtration and capacitive deionization. The advantages and evolution of using conjugated polymers for separation membranes are also explained. On the basis of polyaniline-based gas separation membranes, Chapter 3 briefly describes a project for turning carbon dioxide enriched from power plants into cement using membranes. Chapter 4 lays down the foundation for achieving high power density supercapacitors by freeze-casting as-filtered reduced graphene oxide films. In Chapter 5, aniline tetramers are combined with reduced graphene oxides in order to avoid chain scission and enhance the cycle stability of supercapacitors. In Chapter 6 tetraaniline, which can be dissolved in common organic solvents, is grafted onto different materials, creating hydrophilic and low bio-adhesion surfaces. Chapter 7 reveals the sequence of doping of the conjugated aniline system due to the defined amount of doping sites of tetraaniline and the insufficient amount of dopants added in. In the final chapter, quantified rate constants measured for oligoanilines in aniline electrochemical polymerization systems show different levels of catalytic effects depending on the chain length, capped functional groups, and redox properties of linear aniline derivatives.