Preparation Of Highly Oriented Lamellar Polyaniline Films And Their Properties

Conducting polymers have been extensively studied since the discovery of polyacetylene in 1977.Polyaniline(PANI)is one of the most promising conducting polymers that has received enormous attentions because of its facile processability,unusual doping/dedoping chemistry,reversible electrochemical properties,good environmental stability.Recently,with the development of nanotechanology,many researches have focused on the synthesis of PANI materials with nanostructures in order to improve their performances and expand their applications.PANI with nano-lamellar structure is even more attractive because of its high surface area,distinctive conducting pathways.In addtition,it might be proved useful in the field of bioengineering since its lamellar structure is similar to that of the biofilm.Moreover,it has the potential to be split into two-dimensional(2D)materials.However,it is still challenging to fabricate highly oriented lamellar PANI films with lower surface roughness.Considering above research background,we adopted electrochemical polymerization method to fabricate the highly oriented lamellar PANI films and study their structures and properties.The main contents and results of our researches are summarized as following:1.We fabricated PANI membranes composed of ordered stacking layers on indium tin oxide(ITO)through controlling the concentration of aniline,types of dopant and applied potentials.The results showed that the lamellar structure was affected by the type of dopant and the applied potential.When the dopant is sulfuric acid and the applied potential is in the range of 0.7 ~ 0.85 V versus saturated calomel electrode(SCE),the lamellar amorphous PANI films can be obtained.The stacking period is only 9.0 ? 0.1 ?.2.We adopted various spectra and high resolution atomic force microscopy(HRAFM)to investigate molecular structures and stability of lamellar amorphous PANI films.The results show that the films are composed of linear chains,which are disordered in the xy-plane.However,there are some nano-sized ordered crystalline grains distributing in the amorphous matrix.Taking together,it is these crystalline grains and interchain hydrogen bonds that maintain the stability of lamellar structure.At the same time,we adopted atomic force microscopy(AFM),scanning electron microscopy(SEM)and X-ray reflection(XRR)to study the growth process of lamellar PANI films and found that the PANI adopted a 2D growth mode.3.We selected different substrates as the working electrod to electrochemically deposite PANI.The orientation and crystal structure depend strongly on the property of the substrate,which however has no effect on the configuration and lamellar structure of PANI.At the same experimental condition(aniline 0.1 M,sulfuric acid 0.5 M,potential versus SCE 0.79 V),we can fabricate highly oriented lamellar PANI crystals on polished silicon wafers.The crystals are composed of high oriented linear chains and have a simple trilinic lattice structure with lattice constants of a = 11.3 ± 0.06 ?,b = 6.3 ± 0.03 ?,c = 9.0 ± 0.03 ?.The PANI crystals also adopt a 2D growth mode.4.Besides optimizing the electrochemical polymerization condition,post-annealing treatment is another effective method to improve the oriented structure of PANI films.When the annealing temperature is increasd to 80 oC,the molecular layers in the amorphous PANI films are stacked parallel to the surface of the substrates with low mosaicity.This method gives a clear guidance for the preparation of other highly oriented lamellar materials.5.In situ XRR and rocking curve measurements were employed to investigate the lamellar structures of as-prepared PANI crystals at high temperature and the annealed crystals.Results show that the lamellar structure of PANI crystals is stable when the temperature is not higher than 70 oC.At the same time,the resistance decreased with the increase of temperature,which is the characteristic of semi-conductor.Moreover,the ultra-thin PANI sheets with the thickness of 16.4 nm could be obtained through liquid-phase exfoliating the lamellar PANI films,indicating that another novel 2D material might be exploited in the future.