Self organizing polymer films—a route to novel electronic devices based on conjugated polymers

Polymer blends are often used in polymer light emitting diodes as a tool to increase the efficiency of the devices. In this report, we show the necessity to take the phase separation properties of such blends into account, as the miscibility of the involved polymers drastically affects the resulting film structure. By using phase separated polymer blends involving conjugated poly(thiophenes) and different non-conjugated polymers as matrices, different types of applications, such as light emitting diodes with improved voltage control of emitted colour, sub-micron size LEDs and anisotropic conductors are demonstrated.     

Self-assembled mono- and bilayers on gold electrodes to assess antioxidants—a comparative study

Oxidative stress is considered as an imbalance of reactive species over antioxidants, leading to diseases and cell death. Various methods have been developed to determine the antioxidant potential of natural or synthetic compounds based on the ability to scavenge free radicals. However, most of them lack biological relevance. Here, a gold-based self-assembled monolayer (SAM) was compared with a gold-supported lipid bilayer as models for the mammalian cell membrane to evaluate the free radical scavenging activity of different antioxidants. The oxidative damage induced by reactive species was verified by cyclic and differential pulse voltammetry and measured by the increase of electrochemical peak current of a redox probe. Trolox, caffeic acid (CA), epigallocatechin gallate (EGCG), ascorbic acid (AA), and ferulic acid (FA) were used as model antioxidants. The change in the decrease of the electrochemical signal reflecting oxidative membrane damage confirms the expected protective role. Both model systems showed similar efficacies of each antioxidant, the achieved order of radical scavenging potential is as follows: Trolox > CA > EGCG > AA > FA. The results showed that the electrochemical assay with SAM-modified electrodes is a stable and powerful tool to estimate qualitatively the antioxidative activity of a compound with respect to cell membrane protection against biologically relevant reactive species.

     

Development of flexible zinc–air battery with nanocomposite electrodes and a novel separator

In this paper, we present the development of flexible zinc–air battery. Multiwalled carbon nanotubes(MWCNTs) were added into electrodes to improve their performance. It was found that MWCNTs were effective conductive additive in anode as they bridged the zinc particles. Poly(3,4-ethylenedioxythiophene)polystyrene sulfonate(PEDOT:PSS) was applied as a co-binder to enhance both the conductivity and flexibility. A poly(acrylic acid)(PAA) and polyvinyl alcohol(PVA) coated paper separator was used to enhance the battery performance where the PVP–PAA layer facilitated electrolyte storage. The batteries remained functional under bending conditions and after bending. Multiple design optimizations were also carried out for storage and performance purposes.     

Gelatin/montmorillonite biohybrid films prepared via a novel photocrosslinking method: structure–properties investigations

Gelatin/sodium montmorillonite (Na⁺MMT) hybrid nanocomposite films were prepared by a new photocrosslinking method using 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone (Irgacure 2959) as a photoactive radical initiator and N,N′-Methylenebisacrylamide (MBA) as a crosslinking agent. The prepared samples were characterized by X-ray diffraction (XRD), differential scanning calorimetry, stress–strain measurements and UV–Vis spectrophotometry. XRD patterns showed the formation of exfoliation structure resulting in considerable improves in mechanical properties of the nanocomposite. Retaining of transparency also suggested that Na⁺MMT nanosheets were uniformly distributed in the gelatin matrix. The tensile strength and Elastic’s modulus of nanocomposites were also improved notably by enhancing amount of Na⁺MMT. Furthermore, gelatin/Na⁺MMT nanocomposites showed a second T _g at a higher temperature in presence of Na⁺MMT.     

Hydrogen evolution on Pt and polyaniline modified Pt electrodes—a comparative electrochemical impedance spectroscopy study

Kinetic of hydrogen evolution reaction, HER, at Pt and polyaniline, PANI, polymer film modified Pt electrodes in the sulphuric acid solution was investigated within the context of possible inhibition of HER by conducting polymers. Pt/PANI electrodes were prepared by electro-polymerization procedure with different quantities of PANI and electrochemically aged in the insulating state prior polarization and electrochemical impedance spectroscopy experiments. Polarization and impedance data obtained in the hydrogen (0.30 to 0.05 V_RHE) and HER (0.00 to ?0.155 V_RHE) potential regions of bare Pt-poly electrode were compared with those of Pt/PANI electrodes. Significant differences of impedance spectra in the hydrogen region of potentials pointed toward domination of hydrogen under-potential deposition, H UPD, at Pt-poly surface and domination of PANI impedance at Pt/PANI electrodes, respectively. Quite similar impedance spectra obtained in the HER region of potentials and Tafel slopes of about 30 mV decade^?1 evaluated from polarization measurements indicated that HER is proceeding by the same mechanism at Pt-poly and Pt/PANI electrodes, respectively. Analysis of respective impedance parameters showed that HER which is easily driven at Pt-poly electrode becomes inhibited to a certain extent at both Pt/PANI electrodes, but more for the one with higher quantity of PANI. These results can commonly be interpreted by HER that is taking place on the Pt substrate underlying more or less porous PANI film acting as a barrier toward electrolyte solution.     

Microbeam grazing incidence small angle X-ray scattering—a new method to investigate heterogeneous thin films and multilayers

The combination of the ID13/ESRF micrometer-sized X-ray beam with the reflection geometry allowed to establish a new scattering method for investigating laterally patterned heterogeneous multilayers and interfaces. This new method—called microbeam grazing incidence small angle X-ray scattering (μGISAXS)—has been applied to a novel gradient multilayer of self-assembled nanometer-sized noble metal clusters on top of a polymer layer, being of significant importance for many technological applications, including biorecognitive sensoring. The new feature of using a 5 μm X-ray beam allows to characterize laterally heterogeneous samples on two length scales, induced by the small beamsize and reciprocal space resolution. From the two-dimensional μGISAXS patterns the three-dimensional structure and morphology of the gradient of gold (Au) clusters was reconstructed using detailed model simulations. Though being a highly complex sample, it turned out that the gradient is characterized by a single parameter, namely the cluster height. Atomic force microscopy (AFM) and optical absorption spectra provide supplementary information and help to enlighten the structure of evaporated gold clusters on polymer layers.     

Preparation and properties of VO2 thin films by a novel sol–gel process

Vanadium dioxide (VO₂) thin films were fabricated using a simple and novel sol–gel process in which V₂O₅ was used as the vanadium source; oxalic acid was used as the reducing agent; and polyvinyl alcohol was used as the film former to control the viscosity of the VO₂ precursor solution and bond vanadium ions. The microstructure and surface morphology of VO₂ films were studied by X-ray diffraction and scanning electron microscopy, respectively. The results showed that using polyvinyl alcohol forms porous nanostructure of VO₂ films with a uniform grain size of ~25 nm. The measured optical reflectance shows well-defined phase transition as observed by an increase of reflectance upon heating above the transition temperature from ~11 to ~30 % at 1,100 nm. Upon cooling, the expected hysteresis is observed.     

Controllable synthesis of silica nanoparticle size and packing efficiency onto PVP-functionalized PMMA via a sol–gel method

This study aimed to investigate synthesis and adsorption behavior of silica nanoparticles onto polyvinylpyrrolidone (PVP)-functionalized poly(methyl methacrylate) under various conditions such as methanol/water ratio, ammonium hydroxide concentration, polymer contents, tetraethylorthosilicate contents, and total volume of solvent via sol–gel method. First, the copolymerization of methyl acrylate as a comonomer and 1-dodecanethiol as a chain transfer agent increased the thermal stability of the product; however, the uniformity of the PMMA particles decreased because of the chain transfer reaction. Second, the adsorption behavior and size of silica nanoparticles could be controlled by adjusting the silica synthesis conditions. The adsorbed silica particle size was greatly influenced by the ammonium hydroxide concentration and the addition of water further enhanced the size increase. However, increasing the water content reduced the packing efficiency of the adsorbed silica particles. Increasing the PVP-functionalized PMMA content at a fixed TEOS content linearly decreased the silica particle size. But TEOS concentration did not significantly affect the silica particle size. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 662–672     

An investigation on a novel PDLC film's fabrication and its electro-optical properties

A polymer dispersed liquid crystal (PDLC) film that has good electro-optical properties is produced by the method of polymerized-induced phase separation. Based on the application foreground, its capability parameters, such as contrast ratio, work voltage, and visual angle, are characterized for the first time by a white light but not a fixed wavelength light. The results show the PDLC film has a low work-voltage of 20 V, more than 150° visual angle, high stability, and long lifetime. The differences between plastic and glass ITO-coated substrates of PDLC films are also studied in this paper. The plastic substrate has better property and will have a wider perspective especially in the portable, tender and folded display devices. Due to adjustable properties of film by electric field, PDLC has the potential application for display device, sensor, switch, grating, and new generation analytical apparatus.     

855 — Electrochemical conversion of lactoperoxidase,ceruloplasmin and alkaline phosphatase on mercury electrodes

Reversible redox conversions of lactoperoxidase, ceruloplasmin and alkaline phosphatase disulfide bonds proceed in phosphate buffer solutions on the d.m.e. Irreversibly adsorbed and denaturated enzyme molecules take part in the process. Enzymes are also adsorbed irreversibly on the d.m.e. from potassium chloride solutions, but the redox conversion rates of disulfide bonds are considerably lower, due to the specific adsorption of chloride ions on the mercury electrode.     

Electrochemical deposition of copper in polyaniline films — number density and spatial distribution of deposited metal clusters

The electrochemical deposition of copper in reduced polyaniline (PAN) films is studied at different polymer layer thicknesses. A saturation in the number density, n₀, of active sites for metal deposition is found at 0.5 μm PAN thickness (n₀=10⁸ cm⁻²). The surface spatial distribution of the deposited copper crystals is analysed in two cases. It is found that nucleation exclusion zones play an appreciable role in the course of the deposition process in thin PAN films. In contrast, a random distribution and a larger number of deposited crystals are obtained in thicker PAN layers.     

Simultaneous formation of ferrite nanocrystals and deposition of thin films via a microwave-assisted nonaqueous sol–gel process

Combination of the surfactant-free nonaqueous sol–gel approach with the microwave technique makes it possible to synthesize Fe₃O₄, CoFe₂O₄, MnFe₂O₄, and NiFe₂O₄ nanoparticles of about 5–6 nm and with high crystallinity and good morphological uniformity. The synthesis involves the reaction of metal acetates or acetylacetonates as precursors with benzyl alcohol at 170 °C under microwave irradiation of 12 min. Immersion of glass substrates in the reaction solution results in the deposition of homogeneous metal ferrite films whose thickness can be adjusted through the precursor concentration. If preformed nickel nanoparticles are used as a type of curved substrate, the ferrite nanoparticles coat the seeds and form core–shell structures. These results extend the microwave-assisted nonaqueous sol–gel approach beyond the simple synthesis of nanoparticles to the preparation of thin films on flat or curved substrates.     

Structural and electrochemical behavior of Mn–V oxide synthesized by a novel precipitation method

Manganese–vanadium oxide had been synthesized by a novel simple precipitation technique. Scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, thermogravimetric analysis/differential scanning calorimetry, and X-ray photoelectron spectroscopy were used to characterize Mn–V binary oxide and δ-MnO₂. Electrochemical capacitive behavior of the synthesized Mn–V binary oxide and δ-MnO₂ was investigated by cyclic voltammetry, galvanostic charge–discharge curve, and electrochemical impedance spectroscope methods. The results showed that, by introducing V into δ-MnO₂, the specific surface area of the mixed oxide increased due to a formation of small grain size. The specific capacitance increased from 166 F g⁻¹ estimated for MnO₂ to 251 F g⁻¹ for Mn–V binary oxide, and the applied potential window extended to −0.2–1.0 V (vs. saturated calomel electrode). Through analysis, it is suggested that the capacitance performance of Mn–V binary oxide materials may be improved by changing the following three factors: (1) small grain and particle size and large activity surface area, (2) appropriate amount of lattice water, and (3) chemical state on the surface of MnO₂ material.     

Fe/Sr ratio and calcination temperature effects on processing of nanostructured strontium hexaferrite thin films by a sol?Cgel method

Nanostructured single-phase strontium hexaferrite, SrFe₁₂O₁₉ (SrM), thin films have been synthesized successfully for the first time on silicon substrates using a spin-coating sol?Cgel process. The precursor solution was prepared from metal nitrates, citric acid, and ethylene glycol. The thin films with various Fe/Sr molar ratios of 8?C12 were heat treated at different temperatures from 700 to 900???C. The composition, microstructure, and magnetic properties of the SrM thin films were also characterized. The results showed that the optimum molar ratio for Fe/Sr was 10, at which the lowest calcination temperature for obtaining the single-phase strontium hexaferrite thin films was 800???C. The crystallite size of the resultant thin films was below 50?nm.     

Fabrication of functional nanostructured coatings by a combined sol–gel and plasma-enhanced chemical vapour deposition method

Nanostructures have a wide range of potential applications in industry because they can impart novel mechanical or functional properties to coatings such as abrasion resistance, UV shielding, superhydrophobicity. In this work we present a method for the fabrication of nanostructured coatings with improved mechanical properties, in which sol–gel nanoparticles are deposited on a surface and embedded in a ceramic film by plasma-enhanced chemical vapour deposition. This synthetic strategy is applied to the fabrication of transparent nanostructured antiscratch coatings.     

Competition of anchoring groups in adsorption on gold electrodes—a comparative spectroelectrochemical study of 4-mercaptobenzonitrile and aromatic nitriles

The adsorption of 4-mercaptobenzonitrile (MBN) on a polycrystalline gold electrode has been studied in a spectroelectrochemical approach; results are compared with those of a similar study of the adsorption of benzonitrile and bencylcyanide. Results imply adsorption of MBN via the sulfur atom; in case of the latter, compounds adsorption via the nitrogen atom of the cyano-group is found. In case of MBN, the electron-withdrawing cyano-group causes a substantial weakening of the MBN–gold interaction.