Preparation Of Conductive Composites Based On Nano-poly(3,4-ethylenedioxythiophene) And Its Application In Printed Electronics

As a traditional additive manufacturing process,printing technology has the advantages of low cost,low energy consumption,flexibility,environmental friendliness and suitability for roll-2-roll production.In recent years,there has been a surge of printed electronics in the production of electronic devices and products.In particular,the organic printed electronic devices are more and more popular because of their characteristics of lightness,flexibility,stable performance,easy processing and wide application.The organic light-emitting diodes OLEDs,organic thin film transistors(OTFTs),organic memory,organic sensors,organic photovoltaic cells(OPVs)devices,and smart wearable devices are all the hot topics.Conjugated conductive polymer poly 3,4-ethylenedioxythiophene(PEDOT)with high conductivity,good optical transparency,good thermal stability characteristics are widely used in these fields.But PEDOT material is insoluble in most solvents and is not conducive to printing process.Although PSS can form uniform and stable PEDOT:PSS dispersion in PSS,the addition of PSS leads to the decrease of conductivity of the material and poor environmental stability(Hygroscopicity).In the special functional devices and specific environments,its applicability will be greatly reduced.In order to further improve the performance of PEDOT materials and to better meet the requirements of the printing process,several methods for synthesizing PEDOT materials with nanostructures and nanocomposites are proposed in this dissertation.The corresponding properties of the materials were increased.And the preparation of the functional inks and substrates were used in printed electronics to study their printability and functionality.The specific research contents are as follows:Nano-PEDOT particles with different morphologies and different degrees of oxidation were prepared by reverse interface method via three different systems,which were respectively different temperatures,different proportions of oil and water,and the unoxidized degree.According to the corresponding characterization and testing,the morphology,molecular structure,electrical conductivity,stability and optical properties of the materials were analyzed and the impact of the three reaction conditions on them were discussed.And the application fields were also discussed.The results showed that nanoparticles with higher oxidation degree,smaller size or larger aspect ratio had better conductivity and conversely exhibited semiconducting characteristics and capacitances.These nano-topography PEDOT materials had good dispersion and processing properties.In the application a single function was controllable,affected by fewer factors,and was more stable performance.Nano-PEDOT particles with different morphologies were configured as ink-jet printing inks.PSSNa was used as a dispersant and tackifier to adjust the viscosity of the ink.Non-ionic surfactant was used to adjust its surface tension.The inkjet printability was systematic studied by the piezoelectric inkjet printhead.The printability of the ink was determined by the analysis of ink dispensability and stability,rheological properties,droplet flight speed,the volume of ink droplets ejected,appearance and deposition on different substrates.The results found that nanoparticles with higher oxidation degree,larger aspect ratio and specific surface area had better dispersion.The best surface tension of ink was 30~40 mN/m and the best viscosity was 8~15 mPa·s.The pezoelectric frequency did not exceed 10 kHz with the best printability.Good inkjet printability could effectively solve the production failures and product defects that traditional metal nano inks had been subjected to agglomeration and clogging.And the processing methods used to print with precursors were complicated.And it could give full play to the advantages of printed electronics technology and products.PEDOT:PSS/MWCNTs nanocomposites containing different multi-walled carbon nanotubes(MWCNTs)were synthesized by in-situ polymerization using MWCNTs as a template.The morphology,molecular structure,electrical conductivity,stability and optical properties of the material were measured via the corresponding characterization and testing.The electrochemical cyclic voltammetry and electrochemical impedance spectroscopy were studied for electrochemical properties of the materials.Our results were that PEDOT could be uniformly coated on the surface of MWCNTs by in-situ polymerization and could form a uniform dispersed conductive network in the composite to improve the performance of the materials.However,as the MWCNTs increased,the optical transmission declined.Therefore,the application of optoelectronic devices should not exceed 0.3wt%.A high viscosity electrochromic gelatum ink was prepared utilizing a combination of carboxymethyl cellulose(CMC)and PEDOT: PSS / MWCNTs composite in aqueous solution.The color blocks and patterns were printed by screen printing and assembled into an electrochromic display devices.The electrochromic properties and the printability of the inks were respectively evaluated by their electrochemical and optoelectronic properties measurements.These results showed that the PEDOT:PSS/ MWCNTs ink had higher cyclic stability and current change rate than the pure PEDOT:PSS.The MWCNTs could increase the charge transfer rate and improve the response speed.When the oxidation state producesd discoloration,trace MWCNTs greatly increased the optical density and color difference of electrochromic materials and their devices.Meanwhile,the electrochromic gelatum ink had good dispersibility and stability.It had good printability to print a uniform color patches,fine pattern lines and points.The static electrochromic display could be printed.And a dynamic electrochromic display could also be assembled by printing pixels.In addition,the dried porous structure of CMC played a positive role in improving the electrical properties of functional inks.This property could also be extended to other electronic devices and products.Based on the preparation of nano-cellulose(CNFs)by TEMPO-assisted oxidation,PEDOT:PSS/CNFs nanocomposites were synthesized by in-situ polymerization.Then the silver nanowires were maintained by the polyhydric alcohol reduction through one-pot process.A series of transparent and flexible films were produced by a simple filtration and layer assembly including CNFs film,CNFs-Ag film,PEDOT:PSS/CNFs film and PEDOT:PSS/CNFs-Ag film.Further the corresponding characterization performance were investigated such as the morphology,molecular structure,electrical conductivity,stability,optical properties and electrochemical properties of the material.The results indicated that the thin CNFs films had a transmittance of nearly 90% and could be used as various transparent and flexible substrates of printed electronics.The CNFs-Ag films could be applied as various flexible transparent electrodes.The PEDOT: PSS/CNFs films were very suitable for use as a flexible transparent substrate OTFT and replacement of silicon-based electronic devices due to the certain P-semiconductor and capacitor.PEDOT:PSS/CNFs-Ag film could be used as a special substrate with P-conductive and semiconducting features on both sides.