This paper describes a variety of experiments that reveal the potential application of impedance spectroscopy (IS) measurements to enhance performance of ultrathin polyaniline (PANI)-based films on flexible substrate to control ammonia gas exposure in the 0–20 ppm range. Further, the device is mechanically robust for making electrical contact without lithography. We have employed the IS technique to proper adjust the optimal operation frequency of an easy-to-process, inexpensive and user-friendly PANI-based resistometric detectors in which drift current and delay problems related to electrode effects and dielectric absorption of PANI are insignificant. These requirements place emphasis upon the material and device configuration, and the range of frequencies from 10 to 100 Hz corresponds to the ideal working region to operate the device to unify sensibility inside 5%, reproducibility, linearity, stability and low response time (

/pdf/ammonia-gas-sensor-based-on-the-frequency-dependent-3mtv7v3972.pdf

Ammonia gas sensor based on the frequency-dependent impedance characteristics of ultrathin polyaniline films

In the present work, we concentrate on the study of effects of metallic electrodes, multilayer thickness and temperature in ac and dc electrical conductivity of polyaniline/poly(vinyl sulfonic acid) (PANI/PVS) ultrathin films. The polymer system was obtained from layer-by-layer (Lbl) self-assembly technique on a glass substrate with an electrode array of adhesion layer of NiCr (20 nm) covered with Au (180 nm). We observed a significant and abrupt increase in the value of dc conductivity and a change of ac conductivity behavior of NiCr/Au–PANI/PVS–NiCr/Au structure when the thickness of PANI/PVS system reaches the Au layer. These effects were ascribed to the ideal contact of Au–PANI/PVS and the relative high interfacial contact resistance between PANI/PVS and NiCr, thus reducing the parallel resistance of NiCr/Au–PANI/PVS interfacial layer in an ideal parallel plate capacitor structure. Atomic Force Microscopy images confirm this assumption. Furthermore, the ac conductivity of Au–PANI/PVS–Au structure was typical of solid disordered materials. A model based on carrier hopping in a medium with randomly varying energy barriers was presented for the ac conductivity of the polymer system, which also encompasses the high dielectric constant of PANI/PVS blended films, the neutral contact Au–PANI/PVS, and the electrical resistance of NiCr–PANI/PVS interfacial layer. The model allowed separating the interface and the bulk effects in the electrical response of NiCr/Au–PANI/PVS–NiCr/Au structure and in addition the highest activation energy (35 MeV) correlated with an optimization of hopping distance (30 nm) for carriers jumps in PANI/PVS system.

/pdf/influence-of-nicr-au-electrodes-and-multilayer-thickness-on-3gow6zam7l.pdf

Influence of NiCr/Au electrodes and multilayer thickness on the electrical properties of PANI/PVS ultrathin film grown by Lbl deposition

The application of cashew gum, in particular the one which is abundant in northeastern Brazil, remains limited to the foods and pharmaceutics industry. In attempting to obtain further potentialities of the cashew gum (CG), its electrical applicability needs to be explored. To this end, the CG is incorporated in blends based on PANI to make an innovative thin self-sustainable blend films (PACG) comprising PANI and CG. The blend films were fabricated by adding the CG in the synthesis process of the polyaniline, and they were prepared by the standard “casting” method. The film materials were blending in three different weight ratios (99:1), (95:5) and (80:20). We also fabricated the only PANI film. As PANI has its conductivity enhanced by doping process, the blends and PANI films were doped by using sulfuric acid at 0.05 and 0.1 mol L−1 concentrations. The characterization of the films was carried out by FTIR spectroscopy, thermal analyses and electrical measurements. The FTIR results exhibited the occurrence of a weak and secondary chemical interaction between PANI and CG. Once there was no appearance of new bands, the profile of the FTIR curves was maintained for the blends and no significant shifts were identified for the maximum frequency of bands. The thermal analysis measurements revealed alteration at the thermal stability temperature of blends due to the doping process and indicated that the thermal profile of the constituent materials (PANI and CG) was preserved in the blends. The electrical studies showed that the undoped blend films exhibited a low level of conductivity as the amount of gum increased. On the other hand, the doped films reached a high level of conductivity in comparison with PANI films and the more the amount of CG in the blend the more is its conductivity. For PACG with 20% of gum, σ increased by a factor of 106, whereas in PANI film, it increased by 104 at the 0.1 mol L−1 doped level. These results point to the possibility of using this sort of blend based on polyaniline and cashew gum as an innovative conductive polymer once it exhibits acceptable electrical, structural and thermal properties.

Electrical, structural and thermal properties of new conductive blends (PANICG) based on polyaniline and cashew gum for organic electronic

Ultrasensitive strain sensors have significant practical application in human-motion detection. However, there is still a challenge for developing strain sensors that are capable of detecting high strain and a high gauge factor (GF). The aim of this study was to investigate whether a semiconducting polymer and AC measurements are able to improve the GF of stretchable sensors. We employed complex impedance spectroscopy measurements to adjust the optimal operating frequency and the impedance component for improving the device performance of a polyaniline film on a flexible poly(vinyl chloride):diisononyl phthalate sub-strate. In the DC regime, the sensor revealed linearity and GF ∼18 at 46% strain. oreover, the frequency of 100 Hz corresponds to the ideal work re- gion to operate the device that unifies sensitivity and linearity, as well as to directly correlate GF and Z∗(100) data. The most surprising correlation is with GF from Z”(100), i.e. GF”(100), which is about 9 times higher than GF (DC regime) at 46% strain. The Cole-Davidson approach is developed, in which Z’(f) and Z”(f) are calculated as functions of tensile stress. This model provides the correlation between GF”(100) and the electrical resistance and capacitance of the device, as well as the charge-carrier hopping distance dependence on the tensile stress.

The use of complex impedance spectroscopy measurements for improving strain sensor performance

Polyaniline (PAni) films obtained by means of pulsed potentiostatic electropolymerization were used as hole-transporting layer in organic photovoltaic devices. PAni films were deposited onto Indium Tin Oxide (ITO) from an acid solution containing 0.1 M aniline monomer at pulsed potentials of 1 V and 1.5V. The PAni films were characterized by Atomic Force Microscopy (AFM), Cyclic voltammetry and UV-Vis absorption spectroscopy. The active layer of poly[2-methoxy-5-(3’,7’-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and phenyl-C61-butyric acid methyl ester (PCBM) was spin coated onto PAni films to obtain the ITO/PAni/MDMO-PPV_PCBM/Al photovoltaic device structures. The power conversion efficiency (η) of multilayered devices was evaluated by current density-voltage (J-V) curves. The results indicate that devices obtained with PAni films exhibit a 4-fold increase in conversion efficiency compared to devices without PAni films.

/pdf/eletropolimerizacao-pulsada-para-confeccao-de-camadas-44ow9dbe0a.pdf

Eletropolimerização pulsada para confecção de camadas transportadoras de cargas foto-geradas em dispositivos fotovoltaicos orgânicos

This paper describes a new approach to improve the analysis of surface modification of free-standing semiconducting polymer films emerged from the interfacial interaction between aluminium electrode and HCl-doped polyaniline (PANI) films. The Al–PANI–Al structure was prepared by casting PANI/N-methyl-2-pirrolidone onto a glass substrate and then being sandwiched between Al electrodes after immersion in HCl aqueous solutions and then dried. The Al–polymer interface was investigated by means of complex impedance spectroscopy in the frequency domain on HCl-doped PANI films. The dc conductivity of the interfacial layer between the Al and PANI surface exposed to air during the film processing is higher than those obtained with Al and PANI surface exposed to glass. Raman spectroscopy data confirm this evidence. Here, it is speculated that some dissociated chlorine and aluminium-salt-containing species have contributed as ionic carriers increasing the electrical conductivity of the polymer bulk, and by the formation of an Al2O3 thin layer between the Al and PANI films. An equivalent circuit model considering the influence of Al–PANI reactions on the electrical behaviour of the Al–PANI–Al structure was proposed. Additionally, it was demonstrated that the impedance spectroscopy facilitates the identification of interface modification in the Al–PANI–Al films.

Analysis of the Al-PANI interfaces by complex impedance spectroscopy

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Analysis of the Al-PANI interfaces by complex impedance spectroscopy