Preparation and characterization of silver particulate films on softened polystyrene and poly(4-vinylpyridine) blends

Results of the investigations carried out on the optical properties of silver particulate films deposited at a rate of 0.4 nm/s on softened polystyrene and poly(4-vinylpyridine) (P4VP) blends held at 455 K are reported. Under the conditions of deposition, a sub-surface particulate structure is expected. It had been shown earlier that the morphology of the sub-surface particulate structure is dependent on polymer-metal interaction. In the present studies, an inert polymer like polystyrene (PS) is blended with an interacting polymer P4VP. The optical studies on the silver particulate films deposited on softened blends of PS/P4VP have been carried out. The results show a shift in plasmon resonance to higher wavelength with increasing P4VP concentration of the blends in comparison to that of the films deposited on pure PS. An X-ray photoelectron spectroscopy study at two different electron take off angles indicates the formation of subsurface particulate structures for films deposited on blends.     

Electrical behaviour of discontinuous silver films deposited on softened polystyrene and poly (4-vinylpyridine) blends

Results of the studies carried out on the electrical behaviour of silver island films deposited on the blends of polystyrene (PS) and poly (4-vinylpyridine) (P4VP) are presented here. The substrates were held at 457 K, much above the glass transition temperature of both the polymers to ensure sufficient polymer fluidity during deposition, to obtain a sub-surface particulate film. A constant deposition rate of 0.4 nm/s was used throughout the study. Films on softened PS gives rise to a very high room temperature resistance approaching that of the substrate resistance due to the formation of a highly agglomerated structure. On the other hand, films on softened P4VP gives rise to a room temperature resistance in the range of a few tens to a few hundred MΩ/, which is desirable for device applications. The blends of PS and P4VP show room temperature resistances in the desirable range even at a PS/P4VP ratio of 75:25. The films show an increase in resistance when they are exposed to atmosphere. This is attributed to the oxidation of silver islands. The film resistances in the desired range could be obtained even after exposure to atmosphere up to a PS concentration of 50%.     

Preparation and characterisation of silver particulate films on softened polystyrene substrates

The preparation of silver particulate films on softened polystyrene (PS) substrates and their characterisation using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and optical absorption spectroscopy is reported in this paper. Silver films of 150 nm thickness were vacuum deposited onto PS coated glass substrates held at temperatures in the range 415–475 K at different deposition rates of 4 to 12 Å/s. SEM studies indicate that films deposited at 415 K are close to a semicontinuous structure and the structure is discontinuous at higher temperatures. The film morphology is strongly dependent on the deposition rate at any given substrate temperature. The film agglomeration increases with increasing rate of deposition. In the XPS studies, considerable attenuation of the signal corresponding to silver is observed at lower electron take of angles (ETOAs). This indicates that Ag is formed beneath the PS surface. Optical absorption studies showed an interesting red shift of the plasmon resonance wavelength for lower deposition rates again indicating that a sub-surface particulate structure is formed at lower deposition rates. These results are consistent with reported observations.     

Electrical behavior of silver particulate films deposited on 8 MeV electron beam irradiated softened polystyrene substrates

Results of the investigations carried out on the electrical behavior of silver particulate films deposited on electron beam irradiated polystyrene (PS) coated substrates held at a temperature of 455 K in a vacuum of 8 × 10⁻⁶ torr at a constant deposition rate of 0.4 nm/s are reported. It is known that when metals are evaporated on to softened polymer substrates, subsurface particulate structures are formed whose morphology is dependent on deposition parameters. Further, it was shown that the morphology is dependent on polymer-metal interaction. The present work demonstrates that the polymer-metal interaction can be brought about in inert polymers like PS by electron irradiation. The results indicate that the films deposited on PS irradiated to a dose of 20 and 25 kGy gives rise to smaller clusters with smaller inter-cluster separation, better suited for sensor applications. The induced polymer-metal interaction is attributed to the creation of free radicals due to the 8 MeV electron irradiation.     

Epoxy resin cured with poly(4-vinyl pyridine)

Poly(4-vinylpyridine) (P4VP) was used as the macromolecular curing agent to prepare epoxy networks. The crosslinking structures were investigated by means of Fourier transform infrared spectroscopy (FTIR). It is identified that depending on the ratios of DGEBA to P4VP, different reactions dominated the formation of the crosslinking networks, which were involved the formation of pyridone (or cyclic amide) resulting from epoxide groups of DGEBA and pyridine rings of P4VP, the Diels-Alder reaction of in situ formed conjugated 3,5-diene in a 6-member ring and the homopolymerization of DGEBA initiated by pyridine moiety of P4VP. Differential scanning calorimetry (DSC) showed that all the DGEBA-P4VP co-crosslinked thermosets displayed single glass transition temperature (T_g), suggesting that the crosslinked networks are homogenous. In addition, it is noted that the T_g's of the DGEBA-rich network are greatly dependent on the molecular weight of P4VP used.     

Sorption of phenolics onto cross-linked poly(4-vinyl pyridine)

In order to explore the possibility of using cross-linked polymer of 4-vinyl pyridine as sorbent for removal, separation and recovery of phenolic species, the sorption behaviour of a number of model phenolic compounds, differing from each other in acidity and molecular size, has been studied, using the vinyl pyridine polymer both in the free-base form and in salt form. The phenolic compounds used include phenol, p-cresol, p-chlorophenol, p-nitrophenol, m-aminophenol, polyphenol and lignin. The sorption of phenolic compounds with the free-base resin affords significantly greater sorption capacity than that with the same resin used in the salt form. The level of pH of the aqueous medium has a marked influence on the sorption of phenols by free-base PVP, the maximum sorption taking place at lower pH for more acidic phenols, which is in accord with the hydrogen bonding mechanism of phenolics sorption. The Freundlich isotherm equation provides an adequate fit to the sorption data, while the coefficient of the isotherm equation bears a distinct relationship to the acidity of the phenolic sorbate. A simplified rate equation based on the concept of linear driving force fitted the initial sorption rate data well, yielding a value for the particle-diffusion control rate coefficient for each phenolic species. Substituted phenols have lower intraparticle diffusivities than phenol, with the diffusivity decreasing as the size of the substituent group increases. Lignin undergoes much stronger interaction with the resin than do the other phenols. Consequently, while the sorbed phenols are all easily eluted by dilute alkali, lignin sorbed onto the resin is however removed only with considerable difficulty.     

Electrical behaviour of discontinuous silver films deposited on compatible Polystyrene/Poly (2-vinylpyridine) composite

Polystyrene (PS) and Poly (2-vinylpyridine) (P2VP) was melt blended. The compatibility of PS/P2VP was investigated by differential scanning calorimetry (DSC), Fourier transmission Infrared (FTIR) and scanning electron microscopy (SEM). The results indicated the single glass transition temperature for the blend. Results of the studies carried out on the electrical behaviour of silver island films deposited on the composite of PS and P2VP are presented here. The substrates were held at 457 K, much above the glass transition temperature of the polymers to ensure sufficient polymer fluidity during deposition, to obtain a sub-surface particulate film. A constant deposition rate of 0.4 nm/s was used through out the study. Silver films deposited on softened PS give rise to a very high room temperature resistance approaching that of the substrate resistance due to the formation of a highly agglomerated structure. On the other hand, films on softened P2VP gives rise to a room temperature resistance in the range of tens to a few hundred MΩ/□ which is desirable for device applications. The composite of PS and P2VP show resistances at room temperature. The films show an increase in resistance, when they are exposed to atmosphere. This is attributed to the oxidation of silver islands. The film resistances in the desired range could be obtained even, after exposure to atmosphere with PS concentration of 50%.     

Structural and electrical properties of Al doped ZnO thin films deposited at room temperature on poly(vinilidene fluoride) substrates

Transparent, conducting, Al-doped ZnO films have been deposited, by dc and pulsed dc magnetron sputtering, on glass and electroactive polymer (poly(vinylidene fluoride)–PVDF) substrates. Samples have been prepared at room temperature varying the argon sputtering pressure, after optimizing other processing conditions. All ZnO:Al films are polycrystalline and preferentially oriented along the [002] axis. Electrical resistivity around 3.3 × 10^− 3 Ω cm and optical transmittance of ~ 85% at 550 nm have been obtained for AZOY films deposited on glass, while a resistivity of 1.7 × 10^− 2 Ω cm and transmittance of ~ 70% at 550 nm have been attained in similar coatings on PVDF. One of the main parameters affecting film resistivity seems to be the roughness of the substrate.     

Encapsulation of magnetic nanoparticles in a pH-sensitive poly(4-vinyl pyridine) polymer: a step forward to a multi-responsive system

A multiresponsive system that consists on pH-responsive polymer microspheres with encapsulated iron oxide magnetic nanoparticles that rendered the core magnetic to enable externally controlled actuation under magnetic induction has been developed. The inorganic nanoparticles were first prepared and, then, further encapsulated in a pH-sensitive poly(4-vinylpyridine). These spheres have been obtained by a modification of the simple, rapid and high-reproducible nanoprecipitation method. Magnetic measurements showed that the iron oxide nanoparticles are superparamagnetic and, therefore, able to undergo a local increase of the temperature when an oscillating magnetic field is applied. Magnetically triggered heating and pH sensitivity can be useful for biomedical applications.     

Structural and electrical properties of pyrolytically deposited carmet films

Electron micrographs of Ni-C films (carmet films) prepared by thermal decomposition of nickel acetylacetonate have been used to investigate the relationship between the structure of the films and experimental parameters (e.g. carrier gas, pressure, substrate temperature). The most significant result was that the carbon content of the films could be influenced over a wide range by the substrate temperature. It was therefore possible to produce films with a temperature coefficient of resistivity between +5000 and -2000 ppm/°C.     

Structural and optical properties of layer-by-layer solution deposited Cu2SnS3 films

Cu₂SnS₃ (CTS) is a simple and potential material for low-cost thin film solar cells. The present work incorporates the study of changes in structural and optical properties of layer-by-layer solution deposited CTS films with annealing. Raman spectroscopy is used to ascertain structural modification upon annealing. Increase in annealing temperature leads to a structural transition from tetragonal to cubic phase. Effect of annealing on optical properties of the films is evaluated in the wavelength range of 400–2,400 nm. It is proposed that layer-by-layer growth method fundamentally defines the optical behaviour of these films. Optical constants and parameters such as refractive indices, dielectric constants and electron energy loss function are calculated from transmittance and reflectance data. The refractive indices, n and k are determined to be in ranges of 1.8–2.2 and 0.18–1.2, respectively. The real and imaginary dielectric constants vary from 1.5 to 4.6 and 0.7 to 5, respectively. Dispersion of refractive index is analyzed using two different theoretical models of Wemple–diDomenico and Spitzer–Fan.     

Structural studies of poly(p-phenylene benzbisthiazole) films

Poly(p-phenylene benzbisthiazole) (PBT) is one member of a new class of highly-rigid, linear, thermally-stable aromatic heterocyclic polymers. The role of heat-treatment in the improvement of the perfection of crystallinity and mechanical properties of oriented films is discussed. Part of the heat-treatment process seems to be to increase the conjugation length of the polymer chain by increasing the planarity of the molecule, as revealed by visual colour changes and by differential scanning calorimetry. This may in turn account for the improved quality of crystallinity. Considerable detail can be seen in the electron diffraction patterns of heat-treated films. With the exception of the equatorial diffraction peaks this scatter can be accounted for by the detailed molecular transform of the PBT polymer, suitably cylindrically averaged, indicating that the crystal structure is essentially two-dimensional, that is the chains while closely and regularly packed lack longitudinal register. A two-dimensional unit cell with the corresponding molecular packing is proposed which can satisfactorily account for the observed density and for the equatorial diffraction peaks.     

Synthesis and properties of epitaxial SnO2 films deposited on MgO (100) by MOCVD

Epitaxial tin oxide (SnO₂) thin films have been prepared on MgO (100) substrates at 500-600 °C by metalorganic chemical vapor deposition method. Structural and optical properties of the films have been investigated in detail. The obtained films were pure SnO₂ with the tetragonal rutile structure. An in-plane orientation relationship of SnO₂ (110) [010]//MgO (200) [110] between the film and substrate was determined. Two variant structure of SnO₂ were analyzed. The structure of the film deposited at 600 °C was investigated by high-resolution transmission electron microscopy, and an epitaxial structure was observed. The absolute average transmittance of the SnO₂ film at 600 °C in the visible range exceeded 90%. The optical band gap of the film was about 3.93 eV.     

Structural properties of electrophoretically deposited europium oxide nanocrystalline thin films

The structural properties of nanocrystalline europium oxide (Eu₂O₃) thin films, produced via electrophoretic deposition (EPD), were investigated. We found that EPD from our Eu₂O₃ nanocrystal solutions yielded both translucent films, with uniform size and distribution of the microstructure, and opaque films, with marked anisotropy to the size and distribution of the constituents of the microstructure. The disparity in the film morphology arose from the initial temperature conditions of the nanocrystal solution. The translucent films, produced from pre-chilled (−25 °C) EPD solutions, were bimodal films, comprised of homogeneous, tightly packed, glassy nanocrystalline films interspersed with micron-sized nanocrystal aggregates. In contrast, the opaque films, produced from room temperature solutions, consisted of an irregularly distributed and shaped microstructure. The evolution of the microstructure was monitored for the chilled samples as a function of film thickness (deposition time) and juxtaposed with the resultant structure of the room temperature film. Optical microscopy and scanning electron microscopy were employed to characterize the films.     

Structural and optical properties of pulsed laser deposited V2O5 thin films

Pulsed laser deposited nanocrystalline V₂O₅ thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and optical spectroscopy. The films were deposited on amorphous glass substrates, keeping the O₂ partial pressure at 13.33 Pa and the substrate temperature at 220 °C. The characteristics of the films were changed by varying the laser fluence and repetition rate. XRD revealed that films are nanocrystalline with an orthorhombic structure. XPS shows the sub-stoichiometry of the films, that generally relies on the fact that during the formation process of V₂O₅ films, lower valence oxides are also created. From the HRTEM images, we observed the size evolution and distribution characteristics of the clusters in the function of the laser fluence. From the spectral transmittance we determined the absorption edge using the Tauc plot. Calculation of the Bohr radius for V₂O₅ is also reported.     

Viscoelastic properties of poly(butylene terephthalate)/poly(ethylene naphthalate) blends

Melt blends of poly(butylene terephalate) (PBT) and poly(ethylene naphthalate) (PEN) with 30 and 60 wt% PEN were prepared using a single screw extruder and an injection moulding machine. Stress relaxation tests for the specimens of PBT/PEN blends and the homopolymers were carried out using an Instron testing machine in an Instron environmental chamber. The Taguchi method of experimental design analysed how different levels of temperature, PEN content and initial stress affected the relaxation behaviour of PBT/PEN blends and homopolymers. From the response tables and analyses of main and interaction effects, it was shown that the most significant factor was temperature, followed by PEN content and then the initial stress. Consequently, high temperature, low PEN content and high initial stress speeded up stress relaxation rate of specimens. Interaction effects between factors were insignificant. To fit the relaxation curves of the PBT/PEN blends and the homopolymers at different temperatures, PEN contents and the initial stresses, four different equations were attempted with Matlab™, which determined the coefficients of these functions using the experimental data of stress change with time. The simulated curves from the most suitable function among them were shown using the calculated coefficients to predict the relaxation behaviour of PBT/PEN blends (50% PEN) at temperatures of 30 and 60°C with an initial stress of 7 MPa.     

Conductivity study of solid polyelectrolytes based on hydroiodide salt of poly(4-vinyl pyridine-co-butylmethacrylate), poly(4-vinyl pyridine-co-butylacrylate)

The chain flexibility of poly(4-vinylpyridine) was tried to increase by lowering its glass transition temperature ( T _g ) and by increasing its amorphous region by copolymerizing with butyl methacrylate and butylacrylate which act as internal plasticizer. The copolymers were prepared in five different feed molar ratios to optimize the required properties such as higher room temperature conductivity and better film-forming capacity. The conductivity and conduction behaviour of the copolymers, as well as their hydroiodide salts have been reported. There was about 10³–10⁴-fold increase in room temperature conductivity of these plasticized polyelectrolytes.