| Transparent Conducting film is an important kind of photoelectric materials, with low resistance and high transparence. Transparent conducting films can be used in flat panel displays, low-e windows, photovoltaics, electrochromic devices and anti-static coatings. Many kinds of inorganic transparent conducting films have been investigated, such as In2O3: Sn (ITO), Sb:SnO2 (ATO) and ZnO:Al (ZAO). However, they have some disadvantages, for example, poor adhesion property on the flexible substrate, and hard to be deposited on the polymer substrate due to the high synthetic temperature, which limit their further applications. Conducting polymer is also an important kind of conducting materials. Among various conducting polymers such as polyaniline, polypyrrole and polythiophene, polyaniline is widely investigated due to its environmental stability, promising chemical, electrical and optical properties, as well as its unique redox tenability. However, poor mechanical properties and poor thermal stability have limited the applications of polyaniline. Composites incorporated by inorganic components and organic polymers can enhance the transparency, surface hardness and heat resistance of polymers.In this paper, dodecylbenzene sulfonic acid-doped polyaniline (DBSA-PANI) was synthesized via the emulsion polymerization, and inorganic acids (HC1, HNO3 or H2SO4) were added to adjust the structure of the emulsion system and improve the structure of polyaniline. Then, the hybrid sol solution was prepared by the obtained polyaniline and organoalkoxysiloxane through a sol-gel process. The transparent hybrid conducting films were deposited by dip-coating method. The organoalkoxysiloxanes used in the experiment were y-glycidoxypropyltrimethoxysilane (GPTMS) and y-(mercaptopropyl)trimethoxysilane (MPTMS), respectively. The effects of content of components of sol-gel solution on the properties and structure of the hybrid films were investigated by a combination of testing techniques.The results showed that the conductivity of DBSA-PANI was improved, when a certain concentration of inorganic acid was added into the emulsion system. Inorganic acid adjusted the acidity and structure of the emulsion solution at a lower concentration of inorganic acid. The conductivity of the hybrid films increased with an increase of concentration of inorganic acid added in the emulsion solution. However, the structure of the obtained samples was unstable, when the added concentration of inorganic acid was too high, because inorganic acid was incorporated into the polymer chains and became the main dopant for polyaniline. Furthermore, the influence of inorganic acid on the polyaniline chain was related with the bulk volumes and solvation of inorganic acid. Compared with hydrochloric acid, sulfuric acid was easier to replace the DBSA because it was more bulky. Sheet resistance of the hybrid films is lowest, when 1.0 mol/L HCl was added into the emulsion solution.The properties and structure of the hybrid films were affected by the content of components in sol-gel process. Acetic acid was used to play both the roles of reagent and catalyst during the hydrolysis-condensation reaction of organoalkoxysiloxane, which replaced the water and ethanol. When GPTMS was used as organoalkoxysiloxane, the epoxy ring of GPTMS can form a hydroxyl group in acid condition, which is beneficial to the disperseion for DBSA-PANI into the inorganic structure. When the molar ratio of HAc to organoalkoxysiloxane was higher than 0.4, the sturcure of the hybrid films was unstable, since the hydrolysis-condensation reaction of organoalkoxysiloxane increased. Moreover, the content of C impurities increased with an increase of the content of acetic acid, which blocked the transfer of electron in the polyaniline chain and decreased the conductivity of the hybrid films. On the other hand, m-cresol can adjust the acidity of solution and it was also a secondary dopant for DBSA-PANI to enhance conductivity of the hybrid films. However, m-cresol, as a kind of acid solvent, also accelerated the hydrolysis-condensation reaction of organoalkoxysiloxane and affected the stable of the obtained samples. Thus, the better properties and structure of the hybrid films can be prepared with the organoalkoxysiloxane/HAc/m-cresol molar ratio of 1/0.4/5. Furthermore, when MPTMS was used as organoalkoxysiloxane, the mercapto group of MPTMS was easier to be oxidized to sulfonic acid group. Polyaniline can be doped with sulfonic acid group. Therefore, the structure of hybrid films was more stable, when MPTMS was used.DBSA-PANI was the main conducting component of the hybrid films. The effects of content of polyaniline on the structure and properties of the hybrid films were investigated. The results showed that, the inorganic network formed more linear structure with an increase in content of DBSA-PANI, which resulted in the thermal stability decreasing. Furthermore, polyaniline was acidic. The structure of the hybrid films were unstable with an increase of the content of polyaniline, since the hydrolysis-condensation reaction of organoalkoxysiloxane increased. Sheet resistances of GPTMS-PANI and MPTMS-PANI hybrid films were 5.1 kΩ/□and 3.23 kΩ/□, respectively, when the content of polyaniline was 30 wt.%. Visible light transmittance of the hybrid films reached 80%. |
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