390373 Preparation of Conductive Polymer Nanofibers with a Coaxial Nozzle Electrospinning Method
Conductive polymer is a polymeric compound which shows electrical conductivity, and is applied to various fields because of its high electrical conductivity, high flexibility, and lightweight characteristics. Further, nonwoven microfabrics of the conductive polymers are expected to be utilized for the highly sensitive sensors in medical and environmental fields. However, because of their infusible and insoluble nature, process of the conductive polymer nonwoven microfabrics must become a multistep. In recent years, the electrospinning of microfibers has been employed due to its simplicity, versatility, and scale-up opportunities. In the electrospinning, coaxial nozzles are often used as the discharge port for the formation of the fine structured materials. In this study, we developed a single step processing method for the formation of nonwoven conductive polymer fabrics which uses electrospinning method with a coaxial two fluid nozzle of a monomer and an oxidant solution.
3,4-ethylenedioxythiophene (EDOT) was chosen as a monomer due to the facts that poly-EDOT (PEDOT) has a good conductivity, environmental stability, and harmless to the human body. Iron(Ⅲ) p-toluenesulfonatehexahydrate (FeTS), one of the most efficient oxidants for EDOT polymerization and known to produce intrinsically doped and electrically conductive PEDOT, was chosen as a oxidant. Before the electrospinning experiments, appropriate solvent for the synthesizing the PEDOT was examined with a bulk polymerization of EDOT, and acetonitrile was chosen for the solvent. Cellulose acetate (CA) and Poly(methyl methacrylate) (PMMA) were used as matrices for the conductive polymer microfibers. Effects of spinning conditions on the properties of conductive polymer were examined.
The monomer solution was prepared by dissolving the CA powder and the liquid EDOT into acetone or acetonitrile. The oxidant solution was prepared by dissolving the PMMA powder and the FeTS powder into acetone or acetonitrile. Both solutions were filled into grass syringes, and placed in automatic syringe pumps. The grass syringe filled with the monomer solution was connected to the outer tube of the coaxial nozzle, while that of the oxidant solution was connected to the inner tube. Both solutions were fed simultaneously to the coaxial nozzle, and electrospunned to the aluminum foil counter electrode to obtain the PEDOT nonwoven microfabrics. The PEDOT microfibers were characterized with scanning electron microscopy (SEM), mass spectrometric analysis (MALDI-TOF-MS) and four-point probes conductivity measurements.
With the coaxial nozzle electrospinning, nonwoven microfabrics were successfully obtained. Average diameter of PEDOT microfibers were varied from 490.6 nm (PMMA 15 wt%, CA 1 wt%) to 800 nm (PMMA 15wt%, CA 10 wt%) with the change in the CA concentration. This fact indicates that the fiber diameter could be controlled by the concentration of the matrix solution. Conductivity of thus formed microfabrics was the order of 10-3 S/cm, which is the same with the PEDOTS obtained by the bulk polymerization. We are now working on the improvement of the conductivity.