Conducting Polymer Thin Films Research Articles

Effect of Hydration Property of Insulative Surfaces on Polypyrrole Thin Film Formation over the Surfaces

Two-dimensional growth of conducting films at interfaces has been paid attention as a novel process for thin film formation. We have investigated fabrication of conducting polymer thin films at an insulative substrate/liquid interface by electropolymerization. A peculiar liquid structure, where concentrations of monomers differ from those in the bulk solution, is formed near the solid surface. The high concentration of monomer is achieved by choosing an appropriate combination in the affinity among the solid surface, solvents, and solutes [1]. In other words, the concentrations of the solutes near the surface are tunable by designing the affinity. Therefore, the morphology of the conducting polymer should be influenced by the highly-concentrated region of monomers in the vicinity of the insulative surface. In the present study, electropolymerization of pyrrole on the hydrophobic or hydrophilic insulative substrates is evaluated. We mainly discuss the impact of the hydration property of the substrates on the two-dimensional growth. Pyrrole was electropolymerized in an aqueous solution containing 0.4 M pyrrole and 0.8 M LiClO4at the applied potential of 1 V vs. Ag/AgCl sat. KCl for 1 hour. The insulative substrates were immersed in the aqueous solution, and a platinum rod as the working electrode (WE) was perpendicularly contacted to the substrates (Figure 1). The counter electrode (CE) was a platinum ring. Polytrifluoroethylene and borosilicate glass were used as hydrophobic and hydrophilic insulative substrates, respectively. In some experiments, glass substrates whose surfaces were modified with dimethyldichlorosilane to make the surfaces hydrophobic were used. Two-dimensional growth of polypyrrole thin films was observed both on the polytrifluoroethylene and hydrophobic glass substrates. In contrast, the lateral growth of polypyrrole along the insulative substrate was not prominent when using the hydrophilic glass substrate. As shown in Figure 2, the fabricated thin films have the thickness on the order of micrometers. Compared with the length of the films in the growth direction, growth rate in the lateral direction was about hundreds times faster than that toward the vertical direction. Such a lateral growth on the hydrophobic substrate cannot be explained by the Marangoni convection caused by a gradient in surface tension along the interface, although the convection is often regarded as the origin of lateral growth of electrodeposited metal thin films grown at liquid/liquid interfaces [2]. The lateral growth should take place because pyrrole molecules, which are regarded as hydrophobic solute, can be preferentially concentrated near the hydrophobic surface compared with in the bulk solution, while they are excluded from the vicinity of the hydrophilic surface.[1] M. Mizukami, M. Moteki, K. Kurihara, J. Am. Chem. Soc., 124, 12889 (2002).[2] E. Tada, M. Saeki, H. Kaneko, Electrochem. Solid-State Lett., 13, D57 (2010).

An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film

Pressure sensing is an important function of electronic skin devices. The development of pressure sensors that can mimic and surpass the subtle pressure sensing properties of natural skin requires the rational design of materials and devices. Here we present an ultra-sensitive resistive pressure sensor based on an elastic, microstructured conducting polymer thin film. The elastic microstructured film is prepared from a polypyrrole hydrogel using a multiphase reaction that produced a hollow-sphere microstructure that endows polypyrrole with structure-derived elasticity and a low effective elastic modulus. The contact area between the microstructured thin film and the electrodes increases with the application of pressure, enabling the device to detect low pressures with ultra-high sensitivity. Our pressure sensor based on an elastic microstructured thin film enables the detection of pressures of less than 1Pa and exhibits a short response time, good reproducibility, excellent cycling stability and temperature-stable sensing.

Conducting polymer thin films as substrates for cell cultures

ABSTRACTIn biological applications, conjugated polymers offer many advantages compared to inorganic semiconductors, due to their favorable electrical properties and their biocompatibility. Many different parameters affect the cell-substrate interaction and in this work we focus our attention on the role played by the oxidation state and surface morphology of conducting polymer substrates. We realized cell culture substrates using a thin film of a biocompatible conducting polymer widely employed in organic electronics, poly(3,4-ethylene dioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS). The oxidation state of the samples was electrochemically modified through the application of a fixed potential, and they were subsequently characterized by atomic force microscopy and optical spectroscopy. Using these techniques we have been able to measure the oxidation state of the polymer films, and to asses that its surface roughness does not depend on its oxidation state. Furthermore, human dermal fibroblast (hDF) were grown on PEDOT:PSS films with different oxidation state, in order to test their efficacy as cell culture substrates and their biocompatibility.

Modification of Novel Conductive PEDOT:Sulfonated Polyimide Nano-Thin Films by Anionic Surfactant and Poly(vinyl alcohol) for Electronic Applications

Conductive poly(3,4-ethylenedioxythiophene):sulfonated polyimide (PEDOT: SPI) nanoscale thin films were successfully developed by addition of anionic surfactant and poly(vinyl alcohol) (PVA) for potential application in electronic devices. In this work, sodium dodecyl sulfate (SDS) surfactant was introduced into PEDOT:SPI aqueous suspensions to improve the dispersion stability of the particles in water, leading to high transparency and low contact angle of PEDOT:SPI thin films. All of the conducting polymer thin films showed high transparency of more than 85% transmission. Conductivity enhancement and good film-formation properties of PEDOT:SPI were achieved by adding various amounts of PVA to each polymer aqueous suspension because of the resulting conformational changes. The highest conductivity of 0.134 S/cm was achieved at 0.08 wt.% PVA in PEDOT:SPI2/SDS/PVA film, increased by a factor of 3.5 compared with the original material. In addition, PVA also improved the thermal stability of the conductive films, as verified by thermogravimetric analysis (TGA). The interactions between conducting polymers, PVA, and SDS surfactant affecting nano-thin film properties were revealed and investigated. Moreover, the interactions between SDS and SPI were proven to be different from those between SDS and poly(styrenesulfonate) (PSS) in conventional PEDOT:PSS solutions.

Selective deposition of gold nanoparticles on the top or inside a thin conducting polymer film, by combination of electroless deposition and electrochemical reduction

In this paper we present the procedures allowing for synthesis of the composite systems in which Au nanoparticles are located: (i) only on the surface of the polymer film, (ii) only inside the polymer matrix or (iii) both on the polymer surface and in the polymer film. Thin poly(1,8-diaminocarbazole) (PDACz) films were electrodeposited on gold or highly oriented pyrolytic graphite (HOPG) electrodes from acetonitrile solution. Then, Au nanoparticles (NPs) were formed either by electroless deposition on the polymer layer in the solution of HAuCl4 or by electrochemical reduction of AuCl4− incorporated into the polymer matrix, carried out in the solution of HClO4. The amount of deposited Au was determined from electrochemical quartz crystal microbalance measurements and from the reduction charge. The role of protonation of amino groups of the polymer in the process of AuCl4− insertion into the polymer matrix has been discussed. A distribution of Au nanoparticles on the top and inside the polymer film was studied by SEM and TEM images of the polymer cross sections prepared by focused ion beam (FIB) method.

Transparent electrodes based on conducting polymers for display applications

The materials science and engineering related to the fabrication of conducting polymer thin films and the progress in the development of devices integrated with organic transparent electrodes based on conducting polymers for display applications are reviewed. Transparent electrodes are essential components for many display modules. With the evolution of display technologies, conducting polymers are recently emerging as important alternative materials for the fabrication of transparent electrodes. Conducting polymers offer some advantages, such as light weight, low cost, mechanical flexibility and excellent compatibility with plastic substrates for the development of next-generation display technologies and, in particular, are expected to play an important role in the development of flexible display technologies.

Fabrication of a near-infrared sensor using a polyaniline conducting polymer thin film

Near infrared (NIR) photo-responsive polyaniline-based conducting thin films are developed for sensor application. Upon NIR illumination (2.43W/cm2), the electrical conductance of the polyaniline thin films was enhanced 5.9% and the response time was 20s. NIR sensing performance of polyaniline conducting polymer thin film is comparable with that of bolometric carbon nanotube (CNT) network devices with the merits of polymers over CNTs such as processability, productivity and economy.

Controlling Surface Plasmon Optical Transmission with an Electrochemical Switch Using Conducting Polymer Thin Films

AbstractSurface plasmon resonance (SPR)‐enhanced optical transmission is actively controlled by an electrochromism of conducting polymer thin films. Polyaniline and poly(3,4‐ethylenedioxythiophene) thin films are deposited on a thin gold grating surface. SPR‐enhanced optical transmission is demonstrated by irradiating white light on the conducting polymer thin film–gold grating surface and detecting the transmitted light from the back side. The transmission SPR system is combined with an electrochemical setup to manipulate the resonance. The wavelength of the sharp peak in the transmission light spectra is tuned by electrochemical doping/dedoping of the conducting polymer thin films. The present study of controllable SPR‐enhanced optical transmission should provide novel active plasmonic devices such as active bandpass filters or biosensors.

Edge Isolation of Transparent Conductive Polymer (TCP) Thin Films on Flexible Substrates using UV Laser Ablation

The purpose of this study was to directly use the writing techniques for the complex electrode edge isolation of transparent conductive polymer (TCP) thin films by a nanosecond pulsed UV laser processing system. The processing parameters including the laser pulse energy, the pulse repetition frequency, and the scan speed of galvanometers were examined to ablate the TCP films deposited on polyethylene terephtalate substrates of 188 microm thick. The thickness of TCP films was approximately 20 nm. The laser pulse repetition frequency and the scan speed of galvanometers were applied to calculate the overlapping rate of laser spots and to discuss the patterning region quality. Surface morphology, edge quality, and width and depth of edge isolated patterning structures after laser ablation process were measured by a three-dimensional confocal laser scanning microscope. In addition, the electrical conductivity of ablated TCP films was measured by a four-point probes instrument. After isolated line patterning was formed, the ablated TCP films with a better edge quality were obtained directly when the overlapping rate of laser spots, the scan speed, and the pulse repetition rate were 83.3%, 200 mm/s, and 40 kHz, respectively. The better surface morphology of electrode pattern structures was also obtained when the scan speed and the pulse repetition rate were 500 mm/s and 40 kHz, respectively.

Scanned Pipette Techniques for the Highly Localized Electrochemical Fabrication and Characterization of Conducting Polymer Thin Films, Microspots, Microribbons, and Nanowires

AbstractThe limited toolbox for conducting polymer (CP) microscale fabrication and characterization hampers the development of applications such as sensors and actuators. To address this issue, a robust and integrated methodology is presented, capable of electrochemical fabrication and characterization of CPs in a highly localized manner, allowing for CP patterning and spatial mapping of voltammetric response. This is enabled by scanning probe microscopy (SPM) tipped with a single‐barreled micropipette to electrochemically polymerize CP microspot arrays, demonstrated for 3,4‐ethylenedioxythiophene and aniline monomers. Stationary electropolymerization produces individual microspots; lateral movement produces long microribbons; retraction produces extruded microstructures. Subsequently the same SPM setup is tipped with a double‐barreled micropipette to carry out localized cyclic voltammetry. The micropipettes are filled with saline solutions in contact with Ag/AgCl electrodes, forming a thin meniscus of solution at the micropipette tip, which enable an automated approach in air and subsequent contact with the surface. The flexibility of this novel technique is demonstrated by application to 2D poly(3,4‐ethylenedioxythiophene) (PEDOT) microspots, microribbons and nanowires, plus polyaniline (PANI) microstructures and self‐assembled thin films. Finally, setting up a dynamic electrochemical cell allowed for voltammetric–amperometric imaging, simultaneously mapping the morphology and current response of CPs. Future refinements towards the nanoscale through smaller‐tipped pipettes should open up new opportunities for voltammetric response mapping of individual CP nanostructures.

Vapor phase polymerization of poly (3,4-ethylenedioxythiophene) on flexible substrates for enhanced transparent electrodes

Recently, conducting polymer thin films have been investigated as transparent electrodes in photovoltaic devices and organic light emitting diodes. Due to its relatively high conductivity and excellent transmission in the visible region, poly (3, 4-ethyelenedioxythiophene) (PEDOT) has been shown to be a viable option for such applications. Herein described is a method for the vapor phase polymerization (VPP) of transparent PEDOT thin film electrodes on flexible polyethylene naphthalate (PEN) substrates and the comparison of this VPP method with two current approaches to PEDOT deposition: solution-based in situ polymerization and spin coating a dispersion of PEDOT:PSS. Electrical conductivities and UV–vis transmittances were measured for films produced by each of these methods, with VPP PEDOT showing both the highest conductivity (approx. 600 S/cm) and transmittance (>94% at 550 nm). The surface morphologies of the films were compared using AFM and SEM imaging. The stability of these PEDOT films, stored under ambient conditions, was investigated by monitoring the conductivity and transmittance of the thin films over time.

Radically simple technique developed to grow conducting polymer thin films

Radically simple technique developed to grow conducting polymer thin films

Nonequilibrium behavior of thin polymer films

The rheological behavior of 100-nm-thick polystyrene films cast from various solvents was examined using an electric field to weakly perturb the free surface of the polymer melt. The effective viscosity and residual stresses of the as-spun films are seen to strongly depend on the properties of the casting solvent and the solvent quality. Both effects are explained in terms of the coil dimension at the solvent-polymer composition at which the film vitrifies. The more compact chains in a near-Θ-solvent are less entangled and less deformed when quenched to the dry melt compared to the more swollen chains in an athermal solution. Despite chain conformations that are further from equilibrium for the Θ-solvent cast chains, these films have reduced stored stresses compared to the chains cast in films from athermal solvents. A more detailed analysis of the data suggests that the formation of a surface-near region with more strongly deformed chains during spin coating. Since thermal equilibration of spin-cast high-molecular-weight films is unpractical, solvent vapor annealing was used to equilibrate films on timescale of a few hours.

MOBILITY OF ADSORBED POLYMER CHAINS

Abstract The behavior of thin polymer films adsorbed on a graphite surface was investigated by means of atomic force microscopy. Via force–distance curves, which were recorded for layers of polyisoprene adsorbed on graphite [highly ordered pyrolytic graphite (HOPG)], a two-layer system was found. The upper layer proved to be soft and not in the glass state. No indications supporting the supposition of an additional glasslike polyisoprene layer underneath this soft layer could be found. Thus, if such a glass layer exists on the HOPG surface, the upper limit of its thickness is set to 3 nm. On the other hand, polystyrene adsorbed on graphite is in the glass state independent of thickness.

Comparative analysis of sensor responses of thin conducting polymer films to organic solvent vapors

A comparative analysis of responses of thin films of various conducting polymers (polyaniline, polypyrrole and poly-3-methylthiophene) to the vapors of polar as well as low- and nonpolar organic solvents was performed. Conductivity measurements, infra-red and electron paramagnetic resonance spectroscopy were used to characterize responses of the polymer films doped with different dopants. Main physical and chemical factors which define the magnitude of the response to the studied analytes were determined. It was shown that the differences in response of conducting polymer films are conditioned by the influence of chemical structure of the polymer and its dopant, and also by different nature of their doping.

Possible origin of thickness‐dependent deviations from bulk properties of thin polymer films

Journal of Polymer Science Part B: Polymer PhysicsVolume 48, Issue 24 p. 2544-2547 Viewpoint Possible origin of thickness-dependent deviations from bulk properties of thin polymer films Günter Reiter, Corresponding Author Günter Reiter guenter.reiter@physik.uni-freiburg.de Physikalisches Institut, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, GermanyPhysikalisches Institut, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, GermanySearch for more papers by this authorSimone Napolitano, Simone Napolitano Laboratory for Acoustics and Thermal Physics, Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, BelgiumSearch for more papers by this author Günter Reiter, Corresponding Author Günter Reiter guenter.reiter@physik.uni-freiburg.de Physikalisches Institut, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, GermanyPhysikalisches Institut, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, GermanySearch for more papers by this authorSimone Napolitano, Simone Napolitano Laboratory for Acoustics and Thermal Physics, Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, BelgiumSearch for more papers by this author First published: 07 September 2010 https://doi.org/10.1002/polb.22134Citations: 60Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume48, Issue2415 December 2010Pages 2544-2547 RelatedInformation

Electrochemical Analysis of Conducting Polymer Thin Films

Polyelectrolyte multilayers built via the layer-by-layer (LbL) method has been one of the most promising systems in the field of materials science. Layered structures can be constructed by the adsorption of various polyelectrolyte species onto the surface of a solid or liquid material by means of electrostatic interaction. The thickness of the adsorbed layers can be tuned precisely in the nanometer range. Stable, semiconducting thin films are interesting research subjects. We use a conducting polymer, poly(p-phenylene vinylene) (PPV), in the preparation of a stable thin film via the LbL method. Cyclic voltammetry and electrochemical impedance spectroscopy have been used to characterize the ionic conductivity of the PPV multilayer films. The ionic conductivity of the films has been found to be dependent on the polymerization temperature. The film conductivity can be fitted to a modified Randle’s circuit. The circuit equivalent calculations are performed to provide the diffusion coefficient values.

Electric field induced dewetting and pattern formation in thin conducting polymer film

Electric field induced instability and two-dimensional sub-micropattern formation in thin films of polyaniline (PANi) (conducting polymer (CP)) at different levels of doping with camphor sulfonic acid (CSA) are studied experimentally. Optical microscopic and AFM analysis reveal that the application of electric field across the thin PANi-EB (emeraldine base) film–air interface between two electrodes causes instability and formation of uniformly dispersed sub-micron column/drop like elevations surrounded by annular depression. The number density and height of such pattern increase with voltage increment. Number density analysis reveals that below a threshold voltage, CP (at its base state) behaves like a dielectric polymer. On the contrary, a 50% doped PANi-ES (emeraldine salt) thin film–air interface forms stripe like on-plane pattern instead of columnar patterns while subjected to electric field. Performance study reveals faster response of columnar morphology of PANi-EB while exposed to HCl vapor compared to that of thin films of PANi-EB. The significance is in design of chemical vapor sensor of low diffusional resistance utilizing high surface to volume ratio.

A new interpretation of electrochemical impedance spectroscopy to measure accurate doping levels for conducting polymers: Separating Faradaic and capacitive currents

We report an electrochemical impedance spectroscopy (EIS) based method to measure the doping level of conducting polymers. Using EIS the Faradaic current and the capacitive charging current can be separated without relying on any unverifiable assumptions. We demonstrate the method for three types of conducting polymer thin films that are the basis for many commercial applications (poly(3,4-ethylenedioxythiophene), poly-3-hexylthiophene and polypyrrole).

Fabrication of Near-Infrared Sensor by Using Polyaniline Conducting Polymer Thin Film

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