Electrochemical Synthesis Of Conducting Polymer In Hydrophobic Ionic Liquid Based Microemulsions Stabilized By Anionic Surfactant

Conducting polymers are widely used in fields of anticorrosive coatings,supercapacitors,sensors and so on because of their unique photoelectric properties.Chemical oxidation and electrochemical oxidation are conventional methods for preparing conducting polymers.Generally speaking,the electrochemical method has some advantages over the chemical one in view of no additional oxidant,easy film formation and high product purity.The electrolyte for the electropolymerization of conducting polymer has been demonstrated to be a crucial effect on the properties of the resulting polymer.Compared with traditional water or organic solvents,ionic liquids have the characteristics of wide electrochemical window,low saturated vapor pressure and good ability to dissolve organic polymer monomers.In recent years,they are often used as media for the electrochemical synthesis of conducting polymers.Considering the facts that the conductivity of a microemulsion stabilized by ionic surfactant is usually higher than that by nonionic surfactant,and that anionic surfactant aggregate has a catalytic effect on the electropolymerization,it is anticipated that the hydrophobic-ionic-liquid-based microemulsion stabilized by anionic surfactant is better suited to the electropolymerization.For the demonstration,two attempts have been made in this thesis:1.Electropolymerization of[HNPD][NTf₂]in anionic surfactant stabilized hydrophobic ionic liquid based microemulsionFirst the hydrophobic functionalized monomer N-phenyl-p-phenylenediamine bis（trifluoromethanesulfonyl）imide（[HNPD][NTf₂]）was synthesized by acid-base neutralization method,and the resulting monomer was characterized by ESI/MS,NMR and FTIR spectroscopies.The monomer was then electropolymerized in an anionic surfactant[AOT]-（bis-（2-ethylhexyl）sulfosuccinate）stabilized[Bmim][NTf₂]（1-butyl-3-methylimidazolium bis（trifluoromethanesulfonyl）imide）based microemulsion,which was formulated based on the phase triangle of the pseudoternary system at 25℃.The physicochemical properties of the HIL-based microemulsion such as the conductivity,the solubilization capacity toward the[HNPD][NTf₂],and the electrochemical window were determined,and the results show that the ionic liquid based microemulsion is suitable for the electropolymerization of[HNPD][NTf₂].The electropolymerization behavior of[HNPD][NTf₂]in H₂O/[Bmim][NTf₂]/[C2mim][AOT]/n-C4H9OH（δ=0.245）microemulsion system indicate that the water content（i.e.,microstructure）of the system has a significant effect on the initial oxidation potential of[HNPD][NTf₂],the deposition rate of polyaniline,and the morphology and electrical activity of the resulting polyaniline films.The higher the water content in the microemulsion,the lower the initial oxidation potential of the monomer,the faster the deposition rate of the polymer,and the higher the electrochemical activity of the resulting polymer.FTIR and XPS spectra show that the PANI electrosynthesized in the microemulsion is co-doped by both[AOT]-and[NTf₂]-.Compared with the neat ionic liquid,the ionic liquid microemulsion can not only significantly reduce the initial oxidation potential of[HNPD][NTF2]and improve its electropolymerization rate,but also help to greatly reduce the amount of expensive ionic liquid and control the morphology of the polymer synthesized.This study provides a new strategy for the development of green and controllable preparation of conducting polymers.2.Electropolymerization of EDOT in anionic surfactant stabilized hydrophobic ionic liquid based microemulsionHere,an anionic surfactant[AOT]-stabilized H₂O/[Omim][PF₆]（1-octyl-3-methylimidazolium hexafluorophosphate）microemulsion has been tried for the first time as medium for the electropolymerization of 3,4-ethylenedioxythiophene（EDOT）.To formulate AOT-stabilized[Omim][PF₆]-based microemulsions of different water contents,the phase triangle was determined at 35℃.Measurements of the conductivities of the microemulsions,their electrochemical window and their solubilization capacities toward EDOT show that the present[AOT]-stabilized ionic liquid microemulsion is a good medium for the EDOT electropolymerization.Studies on the process of the electropolymerization of EDOT in this[Omin][PF₆]based microemulsion indicate that the water content（i.e.,microstructure）of the microemulsion medium is an important factor affecting the onset potential and the deposition rate of the PEDOT.The morphology and the doping level of the as-prepared PEDOT are also found to be correlated with the water content of the ionic liquid microemulsion.The microemulsion with higher water content results in a PEDOT with better electroactivity and higher doping levels.FTIR spectra and XPS analysis show that the PEDOT electrosynthesized in the microemulsion is co-doped by both[AOT]-and[PF₆]-.Compared with the neat[Omim][PF₆],the use of the ionic liquid microemulsions can reduce not only the consumption of the expensive ionic liquid,but also the onset potential for the electrooxidation of EDOT.Moreover,by tuning the water content of the medium,the electrochemical performance of PEDOT could be regulated accordingly.Under the identical deposited charge,the PEDOT originated from the high water content microemulsion（50%H₂O μE）has higher specific capacitance（124 F g-1）than that from neat[Omim][PF₆]（117 F g-1）.It follows that the present ionic liquid microemulsion is a good medium for EDOT electropolymerization.The present study lays a foundation for the green and low-cost preparation of high-performance conducting polymers.