Preparation And Characterization Of Conducting Polymer Nanomaterials

In recent years,conducting polymer nanostructure has been attracted more attentions due to their excellent optic,electric and gas sensitivity performances.Based on a new type of conducting polymer poly(3,4-ethylenedioxythiophene)(PEDOT),this paper focused on the preparation and characterization of PEDOT nanostructure with different method.The deep and detailed investigation on optical,electrical and gas sensitivity of PEDOT nanostructure was carried out.Furthermore,the application of PEDOT nanostructure to improve orangic electric device performance was also included.The main results are as follows:1.Based on reversed micelle method,small-sized PEDOT nanoparticles was prepared and different methods were utilized to characterize this nanoparticles,such as ultraviolet/visible(UV-Vis) spectroscopy,Fourier-transform infrared(FT-IR) spectrum,X-ray photoelectron spectroscopy(XPS),scanning electron microscopy (SEM) and so on.The results showed that the amount of oxidizer,ultrasonic treatment,polymerizing temperature and doping degree has different influence on morphology,electrical ability and gas sensitivity of PEDOT nanoparticles.The bragg peak of nanoparticles at 6.7°,12.7°,25°was observed by XRD and this well orientation of molecular chain was due to the effective doping of toluene-p-sulfonic acid,which also resulted in an enhancement of thermal stability of nanoparticles than conventional PEDOT.A firstly investigation of gas sensitivity of PEDOT nanoparticles to HCl gas was carried out,and it has been found that the response time of PEDOT nanoparticles deposited QCM to 20 ppm HCl gas was about 20 S and well reproducible sensitivity of QCM device was achieved.Furthermore,the nanoparticles exhibited well detecting ability to lower gas concentration(5 ppm) than conventional one and we ascribed this phenomenon to a larger surface area of nanoparticles,which provid good condition for the adsorption and desorption of analyte gas.2.PEDOT nanotube was fabricated by a template synthesis method.The diameter of this nanotube was about 400～500 nm,which was accordance to the size of porous AAO template,which indicated that size and shape of the obtained PEDOT nanotube can be adjusted by the template.It was presumed that two processes happen successively during the formation of nanotube.The first step was the soaking of polymerizing solution into porous template,and the second step was the adsorption of free charged cationic group and doped PEDOT onto the negative charged template surface.A XRD investigation showed well orientation of PEDOT chain in tube was formed during the synthesis process and it was also found that different arranging of molecular chain reduce the ordered structure of PEDOT nanotube.The single nanotube exhibited a conductivity about 5.5～17.6 S/cm,which was higher than a nanotube pellet due to the high contact resistance between adjacent nanotube.This nanotube showed different sensitivity to varied volatilization gas,and especially showed fast response to the methanol and ethanol than conventional bulk material.The response time of PEDOT nanotube to 1000 ppm methanol was 10～20 S and the reproducing time of tests was more than 15, which due to the larger surface area and better orientation of PEDOT molecular chain in nanotube.3.A Langmuir-Blodgett(LB) inducing method was firstly used to prepare single layer and multilayer conducting composite PEDOT-PSS film.The film-forming ability of ionization ODA and ODA-SA monolayer spread on PEDOT-PSS nanoparticles subphase and the behavior of ODA/PEDOT-PSS assembly particles on pure water were firstly investigated.The results indicate that nanoparaticles in suphase pack the ionization monolayer and stable complex Langmuir film was formed at air/water interface.It has been found that the best film-forming conditions for composite film were as follows:molar ration of ODA to SA was 2:1,suphase temperature was 23 centigrade,concentration of PEDOT-PSS in subphse was about 1×10^-3 M, compressing speed and deposition speed were 5 mm/min and 1 mm/min respectively. The SIMS and XRR investigation showed that this film exhibited well ordered layer structure.Distinct interface was formed between ODA and PEDOT-PSS layer and single layer thickness of PEDOT-PSS was about 23 nm,which was well accordance to the size of PEDOT-PSS nanoparticles.Different structures were designed to test the conductive ability of these composite films and a varible range hopping(VRH) model was used to explain the film conductive mechanism.The results indicated that a 3D-VRH model explained well of transferring of charge carrier in multilayer film.Furthermore,these conducting polymeric LB film were utilized to as the hole transfer layer in OLED device,and an efficiency enhancement of carrier injection was observed,which was ascribe to the ordered structure of these film.However,a further investigation showed that this PEDOT-PSS film had inferior structure ability.4.An arachidic acid(AA)/PEDOT multilayer LB film was firstly prepared through a modified LB film method.UV-Vis,FT-IR,XPS,XRR and SIMS investigation indicated that polymerization of EDOT monomer occurred in nanospace between hydrophilic groups of AA molecular and well ordered PEDOT multilayer film is formed.The reduced ordered structure happened during polymerization of EDOT, which may be caused by a deformation of ordered AA LB film.A four-probe method and semiconductor testing system were used to investigate conductive performance of LB film.Abrupt change of conductivity during the polymerization of EDOT in LB film was observed and this phenomenon may result from an instant connection of conducting channel.It also has been found that AA/PEDOT film exhitbited better conductive ability than ODA-SA/PEDOT-PSS film and spin-coating PEDOT/PSS film,which due to the higherπstructure of PEDOT structure and ordered film structure.The gas sensitivity of PEDOT LB film deposited interdigital electrode to HCl was tested.The results showed that film thickness,treating temperature,deposition speed had different influence on film gas sensitivity.The AA/PEDOT film deposited device exhibited nonlinear behavior to HCl gas at lower concentration(20～60 ppm) and linear response behavior at higher gas concentration was observed.The gas sensitivity mechanism of PEDOT multilayer film can be explained by the charge transfer betweenπsystem of PEDOT and oxidization HCl system,A pervasion theory and energy band theory were utilized to explain the process of adsorption and desorption between HCl molecule and LB film.