Preparation And Properties Of Micro/nano-structrual Polyaniline And Its Nanocomposites

As a member of conjugated conductive polymers,polyaniline(PANI) is unique since the material possesses the advantages of higher conductivity,reversible nonredox doping/dedoping process,better environmental stability and low cost.In recent years,PANI and its nanocomposites with micro/nano-structures has attracted much research interest in the field of potential applications including highly sensitive sensors,radar absorbing materials,electrorheological fluid and information storage material.Although the researchers developed a great amount of methods to fabricated micro/nano-structural PANI and its nanocomposites,all these methods are dependent on template,specific complex chemical reagent or post-synthetic treatments.For PANI nanocomposites,the fundamental research is still at the initial stage,and the synthetic condition is the key aspect to determine the morphology,properties of the product.Therefore developing syntheses that do not rely on templates,structural directing molecules,or specific dopants are important,especially for scaling up to produce large quantities of micro/nano-structural PANI.Simultaneously it is necessary to study the preparation method of PANI nanocomposites,as well as the effect of synthesis condition on morphology and properties.In this dissertation,an interfacial polymerization method is described which enables the synthesis of nano-structural PANI including nanofibers and nanorods. This synthesis is template-free and readily scalable and can be applied to several dopants doped PANI.Based on above research,the electrical behavior at extremely low temperature and thermal aging condition has been studied to reveal transport properties of PANI.Moreover,in-situ UV-Vis spectra are employed to monitor the typical synthesis process.It was found that the expanded conformation of the molecular chain appeared during the synthesis process.The formation mechanism of the PANI nanostructure was discussed.In addition,preliminary discussion has carried on the PANI colloids and PANI/poly(vinyl alcohol) nanocomposites with low electrical threshold.Finally PANI/rod-like attapulgite(AT) nanocomposites with one-dimensional(1-D) nanostructures was prepared via in-situ inverse microemulsion polymerization;a new approach in which we use starch micro-particles template in combination with in situ polymerization to prepare polyaniline/starch composite with shell/core micro-structures.The main results were presented as follows:1) A series of 1-D nano-structural PANI were prepared from interfacial polymerization.The effect of synthesis conditions such as temperature,aniline concentration and dopants on morphology and properties was focused on.The result shows that the morphology of product gradually changes from uniform nanofibers to shorter nanorods with the increasing size of dopant.Compared with PANI from the traditional polymerization,the UV-Vis spectra of nanofibers appear "long tail" phenomenon in long wavelength,which is consistent with expanded conformation of the polymer chain.2) The electrical behavior of PANI nanofibers at extremely low temperature is investigated.A complex model "VRH-CELT" is taken into account to explain transport properties.The conductivity measurement is carried out during aging.The low dimension and the higher surface area of the 1-D PANI allow the evolution of HCl,ring chlorination,chemical crosslinking occur effectively with aging process, indicating that the micromorphology plays an important role in the aging process. From the XRD and FTIR during the aging process,it is found that the aging process of HCl-doped PANI is initiated at the periphery of the crystalline grain and moves progressively towards its center,which is consumed at a much slower rate,finally transforming the material into a poorly conducting phase.3) The "expand-partly doped" stage of interfacial polymerization has been observed in our laboratory at a given reaction condition.In order to analyze the synthesis process,the interfacial polymerization was carried out in the sample cell of the UV-vis spectrometer.The height of sample cell was adjusted to ensure UV or visible radiation passing the aqueous phase where produced PANI diffused.4) By controlling the pH value,the stable colloids of PANI were formed using electrostatic repulsion.A correlation between the stability and zeta potential of PANI particles is established.Positive zeta potential values for the various suspensions of PANI showed that it acquired positive charges after the doping process.It was also observed an increase in zeta potential values as pH decreased.The characteristics of high aspect ratio of nanofibers and the stability of colloids,which allows PANI effectively forming network in matrix and reducing the percolation threshold.The uniform composite films of PANI colloids were successfully fabricated by blending with water-soluble PVA as a matrix.5) PANI/AT nanocomposites with AT as core and PANI as shell was prepared via in situ inverse microemulsion polymerization.TEM shown that PANI/AT composites appear coaxial cable-like nanostructure.Both FTIR and UV-Vis spectra indicate that sodium dodecylsulfonate(SDS) also acts as both surfactant and secondary counter-ion dopant.The final PANI partly doped with this large-size dopant formed partial extended coil conformation in macromolecule chain.Analyses of XRD demonstrated that PANI deposited on the surface of AT without destroying the crystalline structure of AT.Though PANI/AT exhibited better thermal stability compared with pure PANI, electrical conductivity of the nanocomposite was slightly lower that of pure PANI.6) The starch nanoparticles were firstly prepared from non-soluble starch via high-speed shear and ultrasonic methods.Based on the mechanism of ion bond coalescent,the aniline monomer was adsorbed on the surfaces of as-prepared starch nanoparticles.Then starch/polyaniline nanocomposites with core-shell structures were successfully prepared.It was found from UV-Vis spectra and FTIR spectra that the competing doping behavior exists in the final product.TEM and AFM images demonstrated the morphology of "core/shell" nanoparticles with partial semi-IPNs structures.The improvement of thermal stability can be attributed to s-IPN formation. Therefore,conducting channel formation throughout the materials is hampered to some extent which ultimately results in lowering the value of conductivity.Release of moisture and dopant from PANI is much more controlled in IPN,which is the reason for the observed improvement in thermal stability of the materials.