Investigation On The Protonation And Charge Transportation Mechanism Of Polyaniline

Ever since electrical conductivity of doped polyacetylene was found by scientists.conducting polymers as a new kind of functional polymer materials have been widely concerned.As a member,due to available raw materials,simple and diversity preparation methods,excellent physical and chemical performance,unique doping mechanism,etc.polyaniline has been widely used in electronics,electromagnetic shielding,energy storage,metal protection,sensor,etc,and has become an extremely useful conducting polymer.The regulated conductivity of polyaniline is the most important characteristic.At present,relevant experimental investigations have been carried out to study the influencing factors on its conductivity.However,there is still a lack of theoretical calculations on the conductive mechanism of polyaniline.In this thesis,according to the experiment,the charge transport property of polyaniline was investigated from the micro level using theoretical calculation methods.This study has potential value in improving the performance of polyaniline in electronic devices.In this thesis,the electrical properties of polyaniline were studied through experimental and theoretical methods.Firstly,the doped,dedoped,redoped polyaniline and polyaniline with different doping levels were prepared,and the conductive and dielectric properties of the as prepared polyaniline were experimentally investigated.Secondly,the protonation mechanism of polyaniline was studied through theoretical calculations.Thirdly,a theoretical calculation method was used to study the effect mechanism of polyaniline hydrogen bond on the structure and charge transport properties of polyaniline.Finally,the carrier transport properties of polyaniline and its derivatives were investigated through theoretical calculations.The main conclusions of this thesis are as follows:(1)Chemical oxidation polymerization method was used to prepare doped.dedoped and redoped polyaniline,at the same time,polyaniline samples with different doing degree were also synthesized using the similar method.The micro morphology and structure were characterized using scanning electron microscope,X-ray diffraction and fourier transform infrared spectroscopy.The four-probe meter was used to measure the electrical conductivity,and the vector network analyzer was used to evaluate the electromagnetic parameter of polyaniline.The hydrochloric acid doped and redoped polyaniline have partially degree of crystallinity,showing a certain degree of conductivity and dielectric loss properties.The dedoped polyaniline is amorphous,and its electrical conductivity and complex permittivity are approximately zero.The polyaniline with different doping levels are all worm-like micro-structure,and the micro-structure showed a tendency of becoming longer and thinner as the concentration of hydrochloric acid increased.All the obtained samples showed obvious dielectric relaxation phenomenon.When the concentration of hydrochloric acid was 1.Omol/L,the real part and the imaginary part of the complex permittivity were the largest.At the same time,the highest conductivity value was 1.04S/cm.The reduced particle size of polyaniline the particles and the increased dendritic structures in particle surface facilitate the charge delocalization and thus increase the electrical conductivity.(2)It can be observed from the theoretical study on the protonation mechanism of polyaniline that in the structure aspect,from the emeraldine base to the conductive emeraldine salt,the coplanarity of polyaniline chain is enhanced,which will contribute to the electron transport along the polyaniline.In the process of polaron separation,there is charge transfer from quinoid ring to the benzene ring,which contributes to the improvement of polyaniline conductivity.The theoretical study on the structure and property of polyaniline with different doping degree shows that the intercept of density of states(DOS)at Fermi level increases with the increase of doping degree,and the conductivity of polyaniline shows the similar increasing tendency.(3)Theoretical study on polyaniline hydrogen bonding effect shows that stable hydrogen bonding can be formed between polyaniline and camphorsulfonic acid(CSA)or water molecules.It can be seen from the vibrational spectrum that the formation of hydrogen bond has little effect on the main chain structure of polyaniline.The PANI-H2O hydrogen bond complexes show obvious vibration characteristics of O-H and N-H bonds,and this vibration characteristics are consistent with the corresponding bonds elongation trend.The H2O molecules attracted to the chain structure by hydrogen bond between the polyaniline chains facilitate charge transfer with the polyaniline backbone to change the charge distribution on the chain.(4)Theoretical study on the electronic transport properties of phenyl-terminated polyaniline tetramer(ANIH)and its halogenated derivatives shows that ANIH has relatively preferable coplanarity and conjugation,and the reorganization energy is relatively lower.The orbital electron delocalization of ANIH is more uniform and extensive.There is more extended?-conjugated system and greater electron coupling between adjacent ANHI molecules,which will facilitate the migration of carriers.The electron carrier mobility of ANIH is higher than that of hole carrier mobility,and its maximum carrier migration is 1.3893cm2V-1s-1.