Polypyrrole Thin Films Research Articles

Optical properties of electrochemically synthesized polypyrrole thin films: the electrolyte effect

Polypyrrole thin films are prepared by the potentiostatic mode of electrodeposition at +0:7 V versus a saturated calomel electrode (SCE). The polypyrrole films are prepared in the presence of different electrolytes such as: p-toluene sulphonic acid (PTS), oxalic acid and H2SO4. The prepared films are characterized by UV—vis absorption spectroscopy and normal reflectance measurements. The electrochemically synthesized films are semiconductor in nature. The band gap energy of polypyrrole thin films is found to be 1.95, 1.92 and 1.79 eV for H2SO4, oxalic acid and p-toluene sulphonic acid, respectively. The normal reflectance spectroscopy of polypyrrole films shows that the maximum reflectance is in the presence of p-toluene sulphonic acid; this is may be due to a more distinct microstructure than the others. The optical constants such as the extinction coefficient, refractive index, optical conductivity, etc. are calculated and studied with various electrolytes.

Changes of electrochemical properties of polypyrrole when synthesized in a room-temperature ionic liquid

The room-temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate, BMIM BF4, was employed as electrolyte in the electrosynthesis of thin polypyrrole (PPy) films on a Pt substrate, and the resulting PPy electrodes were electrochemically characterized. Electrochemical impedance spectroscopy (EIS) was used to comparatively investigate the electric behavior of PPy produced in the RTIL and the one produced in a traditional acetonitrile/lithium salt system, and charge–discharge curves in the range 2.0–4.0 V (vs. Li/Li+) were obtained in a 1.0 M LiBF4 propylene carbonate solution. Although a reduction of the specific capacity for the PPy obtained in the RTIL was observed, compared to that of the PPy film synthesized in the acetonitrilic electrolyte, its chronopotentiometric profile presented a plateau in the 2.7 V region. This is a remarkable result, considering that a linear decrease in this profile is usually observed for the majority of conducting polymer cathodes. PPy films obtained in BMIM BF4 presented globular morphology, with a special arrangement of nanoparticles constituting the globules; the EIS results indicated that this nanoscale structure may be contributing to a better definition of the redox characteristics during the PPy charge–discharge processes, as it happens for the well-organized structure of some metal oxides.

Lateral Growth of Polypyrrole Electropolymerized along Hydrophobic Insulative Substrates

Effect of hydration property of insulative surfaces on two-dimensional growth of polypyrrole thinfilm along the surfaces was studied. When a platinum rod electrode was simply placed on an insulative hydrophobicsubstrate immersed in an aqueous solution containing pyrrole as monomer, a polypyrrole thin film started to grow two-dimensionally along the surface toward the counter electrode which was a platinum ring electrode placed around the insulative substrate. Such lateral growth of polypyrrole was not observed on a hydrophilic surface. The mechanism of the lateral growth is significantly different from that proposed for metal thin films grown along air/liquid or liquid/liquid interfaces. The lateral growth of polypyrrole seems to be induced by a highly concentrated pyrrole in the vicinity of hydrophobic surfaces. Finally, we have demonstrated that the lateral growth of polypyrrole recognizes the boundary of hydration property on a glass substrate on which hydrophilic and hydrophobic regions coexist.

Gravimetric detection of theophylline on pore-structured molecularly imprinted conducting polymer

A novel molecularly imprinted conducting polymer (MICP) system with porous thin films of electropolymerized polypyrrole (Ppy) derivatives was successfully developed to detect a specific target molecule (e.g. theophylline). The porous MICP films grown on gold pore arrays through cyclic voltammetry showed increased sensing response in detecting theophylline compared to a conventional planar MICP film due to its improved sensing capacity.

Supercapacitive performance of chemically synthesized polypyrrole thin films: effect of monomer to oxidant ratio

Polypyrrole (PPY) thin films with different PPY monomer to ammonium peroxidisulphate (APS) oxidant molar ratios have been synthesized using simple and inexpensive chemical oxidative polymerization method. An interrelation between the monomer to oxidant molar ratio, morphology and supercapacitive performance of PPY thin films is studied. Initial polymerization conditions strongly affect the morphology and electrical properties of PPY thin films. Thermo-gravimetric and differential scanning calorimetric curves show the thermal stability of PPY up to 483 K. The supercapacitive performance of PPY films is studied using cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. In the present work, PPY films deposited with 0.1:0.2 monomer to oxidant molar ratio (pyrrole:APS) show maximum specific capacitance of 754 F g−1 in 1 M H2SO4 electrolyte at the scan rate 5 mV s−1 in potential window of −0.4 to +0.6 V/SCE.

Highly sensitive, reproducible, selective and stable CSA-polypyrrole NO2 sensor

Camphor sulfonic acid (CSA) doped polypyrrole (PPy) thin film sensors were prepared by spin coating method on glass substrates. Structure and morphology of the CSA doped in PPy films were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM), respectively, which proved that there is a strong synergetic interaction between the CSA and PPy. The prepared gas sensors were tested for different concentrations of nitrogen dioxide gas at room temperature conditions by sensing the changes in surface resistivity of the films with respect to time and the results compared with the data on pure PPy sensor. The CSA doped PPy sensor exhibited better sensitivity, selectivity and stability to NO2 when compared with PPy alone. It was revealed that 30% CSA doped PPy sensor operating at room temperature could detect NO2 gas at low concentration (10ppm) with high selectivity (Q=13% compared to H2S) and high sensitivity (S=52%), with better stability (73%). Plausible NO2 sensing mechanism of the CSA doped PPy sensor is discussed. Also, the synergetic interaction between CSA-PPy and NO2 is carried out using impedance spectroscopy and the results are explored.

Highly selective and sensitive room temperature NO2 gas sensor based on polypyrrole thin films

Polypyrrole (PPy) was successfully prepared via chemical oxidation polymerization technique using pyrrole as a monomer and ammonium per sulphate (APS) as oxidant. PPy sensors were fabricated on glass substrates using spin coating technique and characterized using FTIR, SEM, AFM and TEM techniques as well as gas sensing performance of prepared sensors towards various reducing and oxidizing gases were studied. Formation of polypyrrole was confirmed by FTIR spectrum. SEM analysis revealed that, polypyrrole film has highly porous granular morphology suitable for gas sensing application. The AFM analysis showed interconnected granular, porous morphology. The gas sensing studies demonstrate that, the PPy sensor showed outstanding gas sensing properties towards NO2 gas operating at room temperature with good selectivity and excellent repeatability. Furthermore, the PPy sensor is able to detect up low concentration of (10ppm) NO2 gas with reasonable sensitivity (12%) and can be reliably used to monitor the concentration of NO2 gas over the range 10–100ppm. The plausible response mechanism of PPy sensor towards NO2 gas operating at room temperature is also discussed.

Constitution of novel polyamic acid/polypyrrole composite films by in-situ electropolymerization

The preparation and characterization of polyamic acid-polypyrrole (PAA/PPy) composite films are reported in this paper. The thin films were synthesized by electrochemical method from a solution containing controlled molar ratio of chemically synthesized polyamic acid (PAA) and pyrrole monomer. Homogenous films were obtained by incorporating PAA into electropolymerized polypyrrole (PPy) thin film. The concentration of PAA (1.37×10−6M) was kept fixed throughout the composite ratio analysis, whilst the concentration of PPy was varied from 1.90×10−3M to 9.90×10−3M. The PAA/PPy thin films were electrodeposited at a glassy carbon electrode (GCE) and characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Atomic force microscopy (AFM), Scanning electron microscopy (SEM) and voltammetry. The composition that best represented the homogenous incorporation of PAA into PPy matrix was observed at a PAA/PPy ratio of 1: 4.13×10−3. This composite was observed to have two sets of coupled peaks with formal potential 99mV and 567mV respectively. The De determined from cyclic voltammetry using the anodic peak currents were found to be twice as high (5.82×10−4 cm2/s) compared to the De calculated using the cathodic peak currents (2.60×10−4 cm2/s), indicating that the composite favours anodic electron mobility. Surface morphology and spectroscopy data support the formation of a homogenous polymer blend at the synthesis ratio of 1: 4.13×10−3.

One-step synthesis of a Si/CNT–polypyrrole composite film by electrochemical deposition

A Si/CNT–polypyrrole thin film was prepared by electrochemical deposition from an aqueous solution containing Si/CNT composite colloids. The proposed co-deposition mechanism involves the rapid electropolymerization of polypyrrole nanowires and the electrophoretic deposition of Si/CNT particles. The CNT coating on the Si particles enables electrophoresis of the Si particles and promotes the incorporation of the particles into the polypyrrole film.

One-pot electrosynthesis of multi-layered magnetic metallopolymer nanocomposites

Researchers have been investigating various methodologies for fabricating well-defined, homogenous composites consisting of nanoparticles (NPs) dispersed in a matrix. The main challenges are to prevent particle agglomerations during fabrication and to obtain nanoparticles whose size distribution could be tuned on demand. One of the methods that can provide these features is electrodeposition. We report for the first time the fabrication of a thin magnetic multilayer nanocomposite film by electrodeposition from one bath containing both a monomer and metal salts. Cobalt and cobalt-nickel NPs were deposited on conductive polymer polypyrrole thin films using different electrodeposition potentials and times. Multilayer nanocomposite films were fabricated by subsequent electrodeposition of polymer and nanoparticle layers. Scanning electron microscopy analysis showed that a wide range of NPs (70-230 nm) could be synthesized by manipulating growth potentials and times. The cobalt-nickel NPs were found to contain hexagonal close-packed (hcp) and face-centered cubic (fcc) phases based on X-ray diffraction and selected area electron diffraction. Magnetic measurements proved that both the single and the multi-layered nanocomposites were magnetic at room temperature.

Fabrication of a room-temperature H2S gas sensor based on PPy/WO3 nanocomposite films by in-situ photopolymerization

An H2S gas sensor for use at room temperature was fabricated by the in-situ photopolymerization of a nanocomposite thin film of polypyrrole (PPy) and tungsten oxide (WO3) nanoparticles (PPy/WO3) on an alumina substrate. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were used to analyze the structure and morphology of the fabricated films. Comparative gas sensing results revealed that the sensor that was based on the PPy/WO3 nanocomposite film had much more response than that based on pure WO3 or PPy film in the detection of H2S gas at room temperature. Microstructural observations revealed that PPy distributed into the PPy/WO3 nanocomposite film. Therefore, a model of the potential barriers to electronic conduction in the composite material was used to determine that the high response was associated with the stretching of the depletion layers at the interface of the PPy with the WO3 film when the detected H2S gases are adsorbed at room temperature. The sensor that was based on a nanocomposite film of PPy/WO3 responded strongly to very low concentrations of H2S gas at room temperature and its use is practical because of it is easy to fabricate.

Enhancing the morphology and electrochromic stability of polypyrrole via PEG–PPG–PEG templating in vapour phase polymerisation

Despite many investigations of the conducting polymer polypyrrole, its ultimate potential for electrochromic and organic electronic applications has been hampered by a lack of electrical stability. In this study the stability of polypyrrole has been enhanced by introducing a triblock copolymer, poly(ethylene glycol) – poly(propylene glycol) – poly(ethylene glycol) (PEG–PPG–PEG), into the oxidant solution in the vapour phase polymerisation (VPP) process. The inclusion of this triblock copolymer produces polypyrrole thin films with (favorably) smooth and uniform morphology, an RMS surface roughness of ca. 4nm, combined with an increase in electrical switching stability and conductivity. When the homopolymers PEG or PPG are employed in the oxidant, the resulting films do not show the same magnitude of stability, morphological or electrical enhancement. Increasing the amount of PEG–PPG–PEG in the oxidant solution yields a decrease in the thickness of the polypyrrole films with a concomitant reduction in the measured band gap and a red shift of the absorbance peak. This enhanced polypyrrole demonstrates the expected electrochromic behaviour, but with a greater than 20-fold increase in electrical switching stability.

Electric field activated nonlinear anisotropic charge transport in doped polypyrrole

Electric field activated nonlinear transport is investigated in polypyrrole thin film in both in-plane and out-of-plane geometries down to 5 K and strong anisotropy is observed. A morphological model is suggested to explain the anisotropy through inter-chain and intra-chain transport. The deviation from the variable range hopping at low temperature is accounted by fluctuation assisted transport. From Zabrodaskii plots, it is found that electric field can tune the transport from insulating to metallic regime. Glazman–Matveev model is used to describe the nonlinear conduction. Field scaling analysis shows that conductance data at different temperature falls on to a single curve. Nonlinearity exponent, mT and characteristic length, LE are estimated to characterize the transport in both the geometries.

Morphological modulation of polypyrrole thin films through oxidizing agents and their concurrent effect on supercapacitor performance

This investigation reports the fabrication of three different morphologies such as mud-like, cauliflower and interconnected nanoparticles of polypyrrole (ppy) thin films through oxidant assisted successive ionic layer adsorption and reaction (SILAR) method. The influence of oxidants like ammonium per sulfate (APS), ferric chloride (FC) and potassium dichromate (PDC) on structural, morphological, surface areas and electrochemical properties of ppy thin films is examined. Among three different morphologies, interconnected nanoparticles shaped ppy thin films provide a unique three-dimensional (3D) network, high surface area and meso-porous structure which satisfy the requirements for better supercapacitive electrode materials. The electrochemical tests manifest the high specific capacitance of 510Fg−1 at a current density of 0.25mAcm−2 with 85% capacitive retention after 1000cycles. These studies propose that the formation of distinct nanostructures through oxidant dependent chemical polymerization route is a straightforward way for improving the electrochemical properties of ppy based supercapacitors.

Electrodeposition of Gold and Polypyrrole Thin Films for Neural Microelectrodes

A low impedance electrode/tissue interface is critically important for neural microelectrodes recording to maintain signal quality. In this study, gold/polypyrrol thin films used to decrease the interface impedance. Gold thin film was electrodeposited by cyclic voltammetry in the potential range of-0.3 to 1 volt on the stainless steel surface of microelectrodes with 127 micrometer in radius. Then polypyrrole was electrodeposited on the gold layer. Electrochemical impedance spectroscopy tests were performed for impedance measurement of microelectrode surface. The effect of morphology and thickness on the impedance of thin film was studied. The results showed that the impedance of the microelectrodes with gold/polypyrrol coatings was 38.2% lower than the electrodes without coating in the neural frequency.

Electrodeposition of Silver On Ultra Thin Polypyrrole Films. Approach to Unusual Nucleation of Metal

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The influence of monomer concentration on the optical properties of electrochemically synthesized polypyrrole thin films

Polypyrrole (PPy) thin films were deposited on stainless steel and ITO coated glass substrate at a constant deposition potential of 0.8 V versus saturated calomel electrode (SCE) by using the electrochemical polymerization method. The PPy thin films were deposited at room temperature at various monomer concentrations ranging from 0.1 M to 0.3 M pyrrole. The structural and optical properties of the polypyrrole thin films were investigated using an X-ray diffractometer (XRD), FTIR spectroscopy, scanning electron microscopy (SEM), and ultraviolet—visible (UV—vis) spectroscopy. The XRD results show that polypyrrole thin films have a semi crystalline structure. Higher monomer concentration results in a slight increase of crystallinity. The polypyrrole thin films deposited at higher monomer concentration exhibit high visible absorbance. The refractive indexes of the polypyrrole thin films are found to be in the range of 1 to 1.3 and vary with monomer concentration as well as wavelength. The extinction coefficient decreases slightly with monomer concentration. The electrochemically synthesized polypyrrole thin film shows optical band gap energy of 2.14 eV.

Electrochemical biosensing based on polypyrrole/titania nanotube hybrid

The glucose oxidase (GOD) modified polypyrrole/titania nanotube enzyme electrode is fabricated for electrochemical biosensing application. The titania nanotube array is grown directly on a titanium substrate through an anodic oxidation process. A thin film of polypyrrole is coated onto titania nanotube array to form polypyrrole/titania nanotube hybrid through a normal pulse voltammetry process. GOD-polypyrrole/titania nanotube enzyme electrode is prepared by the covalent immobilization of GOD onto polypyrrole/titania nanotube hybrid via the cross-linker of glutaraldehyde. The morphology and microstructure of nanotube electrodes are characterized by field emission scanning electron microscopy and Fourier transform infrared analysis. The biosensing properties of this nanotube enzyme electrode have been investigated by means of cyclic voltammetry and chronoamperometry. The hydrophilic polypyrrole/titania nanotube hybrid provides highly accessible nanochannels for GOD encapsulation, presenting good enzymatic affinity. As-formed GOD-polypyrrole/titania nanotube enzyme electrode well conducts bioelectrocatalytic oxidation of glucose, exhibiting a good biosensing performance with a high sensitivity, low detection limit and wide linear detection range.

The effects of electron irradiation on the optical properties of the organic semiconductor polypyrrole

The optical properties of polypyrrole (Ppy) thin films upon 2 MeV electron beam irradiation changes with different doses. The induced changes in the optical properties for Ppy thin films were studied in the visible range 300 to 800 nm at room temperature. The optical band gap of the pristine Ppy was found to be 2.19 eV and it decreases up to 1.97 eV for a 50 kGy dose of 2 MeV electron beam. The refractive index dispersion of the samples obeys the single oscillator model. The obtained results suggest that electron beam irradiation changes the optical parameters of Ppy thin films.

Improvement of adhesion and continuity of polypyrrole thin films through surface modification of hydrophobic substrates

ABSTRACTConducting polymer polypyrrole is reported to have a poor adhesion to substrate which limits its applicability as thin films. In this article, we report synthesis of well‐formed and continuous film of polypyrrole through treatment of hydrophobic substrates. However, in place of the widely used organosilanes, the substrates were simply treated with surfactant cetyl trimethylammonium bromide (CTAB) prior to vapor phase polymerization under controlled environment. Polypyrrole films formed on CTAB pretreated substrates were found to have improved adhesion and continuity compared to the films formed on untreated substrates. The improved adhesion results in better electronic properties as seen during Electron field emission studies. Based on contact angle analysis, we propose that CTAB molecules act as anchoring agents for the oxidant layer on the substrate and hence assist in the deposition of a more continuous polypyrrole film. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39771.