Li-Ming Huang

Synthesis and characterization of soluble conducting poly(aniline-co-2, 5-dimethoxyaniline)

Abstract Copolymers of 2,5-dimethoxyaniline (DMA) with aniline (ANI), poly(DMA-co-ANI), were prepared for different molar feed compositions of DMA/ANI ( f DMA / f ANI ) by chemical oxidative polymerization using ammonium persulfate as oxidant. The copolymers were characterized by elemental analysis (EA), cyclic voltammetry (CV), Fourier transfer infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). EA results show that molar composition of DMA units ( F DMA ) increased with increasing f DMA up to 0.60. A compositional drift in F DMA was noticed when the feed ratio of DMA was increased beyond 0.60. The redox characteristics of the copolymers with different F DMA were found to show variations than PDMA and PANI. UV–Visible spectroelectrochemical studies, TGA and FTIR spectroscopic analysis were used to identify the differences in the optical, thermal properties and structure between the copolymers and PDMA or PANI. The conductivity of the copolymer was found to decrease with increasing F DMA . The copolymers were soluble in N -methylpyrroldione, dimethylformamide, tetrehydrofuran and acetone. The solubility of the copolymers increased with increasing F DMA . The presence of –OCH 3 groups in the phenyl ring of DMA units induced easy oxidation and better solubility for the copolymers in comparison with PANI.

Electrochemical Synthesis of a Polyaniline-Based Conducting Copolymer with —S—S—Links

Electrochemical synthesis of the copolymer of aniline with dithiodianiline, an aniline derivative containing-S-S-links in it, was carried out in 2 M by cyclic voltammetry (CV). In addition, CV was used to evaluate the differences between the electrochemical characteristics associated with growth of the copolymer and polyaniline (PANI). The deposition of copolymeric film was evident from the observed changes in growth rate, redox potentials, and transport mechanisms of deposited films in contrast to PANI. Plausible reaction schemes are proposed on the basis of CV results for the copolymerization. This involves the possible branched structure for the copolymer and corroborated with other characterizations. X-ray photoelectron spectroscopy and scanning electron microscopy were used to determine the nitrogen and sulfur content and the morphological behavior of the copolymer, respectively. The results show that the copolymer possesses a different charge transport mechanism in films and a branched structure as a consequence of incorporation of DTDA units resulting in -S-S- links in the polyaniline structure.

Structural influence on the electronic properties of methoxy substituted polyaniline/aluminum Schottky barrier diodes

Poly(o-methoxyaniline) (POMA) and poly(2,5-dimethoxyaniline) (PDMA) were used for fabricating Schottky diode devices with sandwich structure, as Al/POMA/indium tin oxide (ITO) coated glass and ITO/PDMA/Al. These devices exhibit rectifying behavior with differences in performance parameters like turn on voltage of the device, barrier height and saturation current density. A close comparison of the current (I)–voltage (V) characteristics reveals such differences. Cyclicvoltammetry and UV-Vis spectroscopy of POMA and PDMA films were used to obtain electrochemical and optical properties of the polymers and discussed in support of the observed differences in the electronic properties of the devices fabricated with POMA/PDMA.

An in situ spectroelectrochemical investigation of the copolymerization of diaminobenzenesulfonic acid with aniline and its derivatives

In situ UV-Visible spectroelectrochemical studies on the copolymerization of diaminobenzenesulfonic acid (DABSA) with aniline (ANI), o-toluidine (OT) and N-methyl aniline (NMA) were carried out potentiostatically in aqueous 1.0 M H2SO4 solutions containing the mixture of monomers (DABSA and ANI/OT/NMA) at an optically transparent electrode. Copolymerization studies were performed for different feed ratios of the comonomers. Polymerization of DABSA was also carried out to bring out the differences in the spectral characteristics between homopolymerization and copolymerization. UV-Visible spectra were recorded at various timer intervals during copolymerization and homopolymerization of DABSA. Four absorption bands were noticed for the copolymerization in contrast to the three bands for homopolymerization. The appearance of bands at 672, 633 and 668 nm for copolymerization of DABSA with ANI, OT and NMA, respectively, are attributed to the exitonic transitions associated with these monomer units in the copolymer. The exitonic band of PANI/PANI derivative units that appeared during copolymerization was markedly influenced by the presence of sulfonic acid groups in the copolymer. This was demonstrated by observing its influence in the absence of applied potential and also by following the changes in the band positions through spectroelectrochemical studies on the copolymerization of DABSA with ANI or OT or NMA. The dependences of absorbances on time at the wavelengths corresponding to polaronic and exitonic transitions of the polymers were deduced. The decrease in absorbances of the exitonic band arising from the dedoping caused by sulfonic acid groups in the polymer showed variations in the copolymerization of DABSA with ANI, OT and NMA. The following trend was noticed ANI>NMA>OT.

Improvement of transparent organic thin film transistor performance by inserting a lithium fluoride buffer layer

Pentacene-based highly transparent thin-film transistors which are fabricated by inserting a thin insulating lithium fluoride layer between pentacene and transparent source/drain electrodes are presented. Through this method, device performance can be enhanced dramatically with an average transmittance of as high as 69.72% in the visible region, indicating that the LiF layer is not responsible for optical transmission. For example, there is a significant improvement of a few times with the introduction of the 1-nm-thick LiF layer, the maximum saturation drain current and the field-effect mobility. These improvements are attributed to the energy band realignment and the tunneling process.

Ion-modulated electrical conduction in polyaniline-based field-effect transistors

The electrical characteristics of a field-effect transistor (FET) using bilayer water-soluble polymer electrolytes/conjugated polymer, that is, poly(ethyleneimine) (PEI)/polyaniline (PANI) doped with camphor sulfonic acid (CSA) structure, are discussed. The NH3+ cations from PEI were stuffed into the PANI-CSA to dedope nitrogen (imine) by applying gate voltage, and this results in the achievement of transistor behavior in drain current modulation. The PANI-CSA/PEI-based organic FETs working in depletion mode with a high field-effect mobility of ∼2.48cm2∕Vs at atmosphere conditions are demonstrated.

Organic thin film transistor by using polymer electrolyte to modulate the conductivity of conjugated polymer

This work presents an organic thin film transistor using double polymer layers, polymer electrolyte/conjugated polymer, i.e., poly(diallyldimethylammonium chloride) (PDDA)/poly(diphenylamine) (PDPA) structure. The single mobile anions (Cl−) pending on the PDDA are stuffed into the conjugated polymer to dope the nitrogen atoms (imine) by applying the gate bias, resulting a higher drain current under the same source-drain voltage. The PDDA/PDPA polymer structure working in the enhancement mode which operates under atmospheric conditions as a typical p-channel transistor is demonstrated.

Blending of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) with poly(ethyleneimine) as an active layer in depletion-mode organic thin film transistors

The conjugated polymer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT-PSS) is usually applied in fabricating electrodes of devices. In this work, the applications to organic a thin film transistor with the introduction of poly(ethyleneimine) (PEI) into the PEDOT-PSS are investigated. The conductivity of PEDOT-PSS can be reduced by incorporating PEI into PEDOT-PSS, which can be applied as an active layer instead of electrodes for devices application. Based on the PEDOT-PSS blended with PEI, the fabricated devices posses a depletion-mode transistor behavior with the on/off ratio of about 103 is used. Meanwhile, the role of PEI in PEDOT-PSS to modulate the channel conductivity is discussed.

Plasma treatment on plastic substrates for liquid-phase-deposited SiO2

The liquid-phase deposition method for growing silicon dioxide interlayers on O2∕Ar plasma pretreatment plastic substrates is investigated. The authors found that the ratio of COO (288.9eV) to CH2(284.5eV) increases with the O2∕Ar plasma pretreatment as indicated by x-ray photoelectron spectroscopy. Upon treatment, the interlayer on the plastic substrate is grown, and the quality of the film on the substrate with or without plasma pretreatment is examined by using scanning electron microscopy, etching rate of the oxide layer by dilute HF solution, and surface leakage current measurement. Pentacene-based organic thin-film transistors on dielectric layers are demonstrated. Finally, they also found that this coating can enhance optical transmittance, as demonstrated by ultraviolet-visible spectroscopy measurement.