Preparation And Properties Of Assembled Micro/Nano-Structures Based On Polyaniline And Aniline Oligomers

In recent years, constructing self-assembled micro/nanostructures based on weak interactions among molecules has become a hotspot in the area of materials and chemistry. In this paper, based on the chemical oxidation polymerization of aniline in near neutral aqueous medium, we prepared several sorts of aniline oligomer and polyaniline assembly structures with novel morphologies conveniently and mildly. Through experimental design, the uniformity, controllability, and dispersity of product are obviously improved as compared with previously reported literatures. After carefully investigating the influences of various parameters on the assembly behavior of aniline oligomers and polyaniline, some novel mechanisms are proposed. We also explored structural properties and applications of certain products with unique morphologies. Research details are listed below:(1) Coassembly of aniline oligomers and polyaniline into nail/spindle shaped morphologies and related mechanism analysis.In near neutral aqueous medium, chemical oxidation polymerization product of aniline can be guaranteed with good dispersity by PVP to produce nail/spindle shaped assemblies. Hydrogen bond interactions between carbonyl groups of PVP and amino groups of aniline oligomer are likely responsible for the effective dispersity. Various parameters such as type of dispersing agent, concentration of monomer, and the relative amount between oxidant and monomer jointly determine the morphology of product. To avoid aggregation, the oxidation rate of aniline and the dispersity of product should be effectively controlled. The nail/spindle shaped assembly structures are composed of both aniline oligomers and polyaniline. Formation process is stepwise:preformed round plates composed of aniline oligomers acted as temlates, and subsequently formed polyaniline grew along the spiral patterns of gradient surface and finally evolved into nail/spindle shaped structures. (2) Assembly of aniline oligomers into cross/needle shaped morphologies and related mechanism analysis.In near neutral aqueous medium, using SDS as surfactant, aniline oligomers were assembled into cross/needle shaped morphology when KPS/APS was conducted as oxidant. The products show good uniformity and water dispersity, and can be further deposited onto substrate in large area. Two rates compete with each other to determine the morphology of final product:(1) the generation rate of aniline oligomers;(2) the diffusion and assembly rate between aniline oligomers and SDS. Micelles formed by SDS can enhance the orientation of assembly. The reacting system containing merely aniline, surfactant, oxidant, and water is very simple to act as a model for research in self assembly. In our system, weak interactions such as hydrophilicity-hydrophobicity interactions, electrostatic interactions, and π-π interactions jointly manipulate the formation of assemblies. There are also other uncertain ingredients to affect the assembly process, such as solubility and crystallinity of oxidant.(3) Assembly of aniline oligomers into water dispersible organic nanowires.A novel kind of organic nanowire was obtained through self-assembly of aniline oligomers. Inside nanowires, aniline oligomers were piled up through weak interactions. PVP enhanced the dispersity of nanowires in water, but didn’t direct the growth of nanowires. The obtained nanowires show several advantages:(1) low cost, scalable, and facile in manipulation;(2) well dispersed in water with negative surface charge, thus can act as templates to be covered by inorganic shells;(3) stable in acidic, alkaline, or even boiling water, but can be easily removed by either organic solvent dissolution or calcination;(4) favorable to fabricate open-ended and unbundled nanotubes, laying foundation for production of single tubular nanodevices. Using these organic nanowires as templates, we successfully prepared SiCO2, MnO2, and NiO nanotubes. Not limited, other sorts of organic/inorganic nanotubes may also be produced in aqueous medium by using these templates, such as metal sulfides, metals, and polymers. (4) Wettability response of polyaniline micro-nanometer composite structures according to alkaline/reduction reactions.SDS can act as surfactant and dopant at the same time to control surface morphology and wettability of polyaniline. When the amount of SDS in restricted within the range of0.03g～0.05g (molar ratio of SDS against aniline in the range of0.02-0.04), polyaniline micro-nanometer composite structures with hydrophobic surface can be obtained. On the contrary, insufficient or excess amount of SDS can only lead to hydrophilic surface. SDS doped at polyaniline surface is oriented:the sulfate group of SDS can interact with positively charged nitrogen atom of polyaniline through electrostatic force, and long-chained alkyl groups can face outside to expose hydrophobic end. The wettability of SDS doped polyaniline micro-nanometer composite structures is responsive to either alkaline or reducing agents from hydrophobic to hydrophilic. Alkaline/Reducing agent induced dedoping of SDS is the main cause for this hydrophobic-hydrophilic transformation. Due to difference in reactivity, response speed and time required to reach balance both vary. Specifically, the value of water contact angle at polyaniline surface is quasi-linear to the concentration of sodium hydroxide within the range of10-3～10-1M. As a result, it is possible to estimate the concentration of sodium hydroxide by simply measuring the value of water contact angle.