Studies On The Synthesis And Magnetoresistance Effect Of Conducting Polyaniline Microfiber

Nano-materials can be divided into zero-,one-,and two-dimension.Materials will show different performance with their block materials as their scale enters the nanometer size range.With the development of organic electronics,low dimension of conductive polymers,with its special physical and chemical features such as electrical,optical,mechanical and magnetism properties imply that they play an important role in the areas of photoelectric devices,sensors,displays,storage devices,wearable devices.One-dimensional materials play an important role in making the device flexible because of its unique structural characteristics.One-dimensional organic conductive polymer plays an important role in the field of organic flexible devices due to its unique doping mechanism and easy synthesis characteristics.Especially,due to their own flexible characteristics.In many properties of one-dimensional conducting polymer structure,the organic magnetoresistance effect is a very interesting point.This can promote its practical application in the fields such as magnetic memory and magnetic sensor.In recent years,studies have shown that the nanostructure of conductive polymer has a great influence on its properties,as well as magnetic properties: organic magnetoresistance effect in one-dimensional organic fibers can only be found in 2D structures which consist of 1D fibers,but cannot be found in only-1D fibers.There is a scientific problem that why the organic magnetoresistance effect cannot be observed in the single one-dimensional fibers must be solved in the development process of one-dimensional materials.And the intrinsic reasons can be analyzed quantitatively using the model.In this paper,we rationally designed the chemical synthesis method of onedimensional organic conductive polymer to control its structural morphology.Self-assembly method was used to induce the synthesis of the helical polyaniline(PANI)microfibers.Scanning electron microscopy(SEM)and absorption spectra are used to studied the structure characterization of PANI microfibers.Importantly,the charge transport mechanism and magnetoresistance properties of PANI microfibers are studied.1.The PANI molecules were induced by camphorsulfonic acid in the organic phase and the state of PANI was regulated by adding oxidant.Subsequently,the poor solvent was added to obtain the PANI microfibers.The proportion of good solvent and bad solvent is controlled reasonably.We can obtain the PANI microfibers with regular structured and more than 20 μm length when the proportion of good solvent reaches 35%.UV-vis-NIR image shows PANI microfibers with the doped level of 65%.2.By analyzing the different testing methods,the methods of evaporation and two-electrode with conductive silver paste are compared.The method of electrode with conductive silver paste is considered as the best method to preparation of the device finally.Single helical PANI microfiber are prepared by assembly method.Aniline molecules are arranged in an orderly arrangement along the microfiber growth direction and PANI microfibers have good crystallization characteristics.Current-voltage characteristic shows that the charge transport model in single PANI microfiber has a typical bias dependent characteristic.This is because of the coupling effect between adjacent "metal island" of PANI chain.In this microfiber,both positive and negative magnetoresistance were observed.An apparent positive magnetoresistance(>1%)was found at 50 K,which is much higher than that previous report.As temperature is enhanced,the positive magnetoresistance was converted to the negative magnetoresistance where the transition happened at ca.90 K.Moreover,the magnetoresistance is also sensitive to the applied bias.These observations can be explained by using the combination or competition of electron wavefunction shrinkage effect,quantum decoherence effect,as well as localized states coupling effects.According to the results in this study,we found that single PANI microfiber can provide free network necessary reason for hopping is the necessary condition for organic magnetoresistance effect compared with the two-dimensional structure composed of one-dimensional PANI fibers.