The Formation Mechanism Of Flower-like Nanostructured Polyaniline In The Presence Of L-valine

Conducting polymers have widespread applications in solar cells,light-emitting diodes,gas sensors and controllable electrodes.Compared with inorganic counterparts,they have advantages in improved processability,proton dopability and environmental stability.Their chemical and physical properties can also be tunned by molecular design.However,the performance of organic devices are not as good as the inorganic ones,one of the major reasons is the lack of the understanding of the formation mechanism of these materials.In this paper,we have utilized the synthesis of flower-like nanostructured polyaniline as our model system and explored its nucleation mechanism by NMR,TEM and SEM.Some primary results obtained are presented in below.(1)The reaction conditions for the formation of flower-like polyaniline doped with L-valine via self-assembly process have been optimized.This study suggests that the synthesis of polyaniline thin films with flower-like or sheet-like morphologies strongly depends on the amount of L-valine used in the reaction.(2)To understand the nucleation mechanism of flower-like polyaniline,we have employed in situ 1H NMR to monitor the overall process,moreover TEM and SEM were applied to detect the morphology of the quenched products in the transition period when some major changes were observed in NMR measurements.A careful comparison for samples prepared under varied concentration of L-valine and aniline has revealed that the formation of flower-like nanostructure has a distinct relationship with the following characters from L-valine:1)being as amphoteric,it can be served as the buffering agent to prevent an abrupt protonation of aniline but rather to induce several aniline molecules to share the charges together so that the electron density at each reactive site on aniline can be nearly identical before the polymerization,and thus favors for the formation of phenazine-like oligomers only and a steady proton induced aggregation of these oligomers;2)locating at the outer-most layer of the aggregates upon formation of L-valine stabilized monomer micelle due to its amphiphilic feature,it can not only stabilize the monomers and the nascent produced oligomers but also allow the aggregation of the oligomers to nanosheets and further the nanosheets to nanoflowers to be taken place in the micelle or through fusion of the micelles respectively.In this way,any irregular structural arrangement induced by the disturbance from the reaction system or the surroundings might be eliminated,leading the highly thermodynamic stable product to be produced eventually.(3)Considering the stacking of sheet-like and flower-like polyaniline,they have such a large specific surface area which leads us to believe they might have high electrochemical performance.The measurement suggests that they can display only good performance,but requires to be improved in future.