Impedance spectroscopy of oxidized polyaniline and poly(o-ethoxyaniline) thin film modified Pt electrodes

Impedance spectra of potentiodynamically formed polyaniline (PANI) and poly(o-ethoxyaniline) (POEA), thin film modified Pt electrodes measured at potentials of conductive, emeraldine form in H₂SO₄ electrolyte solution were reported. Specific features of spectra obtained for films of different voltammetric charge densities were modelled and interpreted according to “homogeneous” and “distributed” impedance models. The values of charging capacitances of different PANI and POEA films were found independent of the model used. Charging of polymer films was in terms of both models controlled by charge transport processes being ion diffusion and migration in the first case, and polymer film and ionic conductivities in the second case. Distortion from Warburg-like response observed for both polymer films was explained by either differences in relaxation times of diffusion and migration processes, or by impedance of ionic channels with “anomalous” frequency dispersion. There were some discrepancies between theories and results suggesting that “homogeneous” model was more appropriate for POEA films while “distributed” model was more appropriate for PANI films, at least if both films were formed and measured in presently described conditions.     

Inorganic silica functionalized with PLLA chains via grafting methods to enhance the melt strength of PLLA/silica nanocomposites

The low melt strength greatly limits the application of PLA as biodegradable package materials produced by film blowing method. Modified silica nanoparticles are introduced into PLA matrix to solve this problem in this study. To build Poly (l-lactide) nanocomposites successfully, two kinds of convenient and efficient methods are conducted to synthesize well-defined topological PLLA grafted SiO₂ nanoparticle. One is the ring-opening of l-lactide (Grafting from), and another is nucleophilic addition reaction (Grafting to). The structure, molecular weight of grafted PLLA chains, grafting density, and the thermal decomposition behavior of the nanoparticles prepared by different methods are characterized. By varying the contents of the initiator SiO₂ and the molecular weight of the reacted PLA chains, high density-low molecular weight PLLA grafted SiO₂ are obtained in “grafting from” while high molecular weight-low grafting density PLLA grafted SiO₂ are synthesized in “grafting to”. It is exactly in good agreement with the theoretic model. The spatial distribution of nanoparticles as well as the interaction force between nanoparticles and matrix is critical important to structuring bionanocomposites with desirable properties. So the two kinds of synthesized nanoparticles are introduced into PLA matrix in our contribution to evaluate these two factors, respectively. The TEM and SEM results both reveal the uniform dispersion of nanoparticles after modified. While the extension and shear rheology results show that the long grafted chains covalently connected on the surface of the silica via “grafting to” contribute more to enhance the melt strength of PLA. Meanwhile, stabilized PLA nanocomposites films with modified silica via “grafting to” method are successfully blown base on these researches. The research in this work constitutes a robust way to design melt-strengthen PLA/SiO₂ nanocomposites.     

Preparation and characterization of osmium hexacyanoferrate films and their electrocatalytic properties

Osmium hexacyanoferrate films have been prepared using repeated cyclic voltammetry, and the deposition process and the films’ electrocatalytic properties in electrolytes containing various cations have been investigated. The cyclic voltammograms recorded the deposition of osmium hexacyanoferrate films directly from the mixing of Os³⁺ and Fe(CN)₆³⁻ ions from solutions containing various cations. An electrochemical quartz crystal microbalance, cyclic voltammetry, and UV-visible spectroscopy were used to study the growth mechanism of the osmium hexacyanoferrate films. The osmium hexacyanoferrate films showed a single redox couple, and the redox reactions included “electron transfer” and “proton transfer” with a formal potential that demonstrates a proton effect in acidic solutions up to a 12 M aqueous HCl solution. The electrochemical and electrochemical quartz crystal microbalance results indicate that the redox process was confined to the immobilized osmium hexacyanoferrate film. The electrocatalytic reduction of dopamine, epinephrine, norepinephrine, S₂O₃²⁻, and SO₅²⁻ by the osmium hexacyanoferrate films was performed. The preparation and electrochemical properties of co-deposited osmium(III) hexacyanoferrate and copper(II) hexacyanoferrate films were determined, and their two redox couples showed formal potentials that demonstrated a proton effect and an alkaline cation effect, respectively. Electrocatalytic reactions on the hybrid films were also investigated.     

Evidence for formation of metallo-siloxane bonds by comparison of dip-coated and electrodeposited silane films

It has been amply demonstrated that thin films of organofunctional silanes deposited by dipping or spraying on metals, such as aluminum, can provide protection against various forms of corrosion. In this paper we show that denser films with higher pore resistance and better corrosion protection performance can be obtained if the silane film is produced by electrodeposition rather than by dipping. In such a process the silane reacts with the metal oxide in a different way, and in the case of aluminum, aluminate ions seem to be incorporated into the silane film. The resulting films can protect aluminum alloys against uniform and pitting forms of corrosion in a salt solution for more than 1000 h, which is comparable to the standard chromate-based treatments. This paper discusses the protection mechanism in some detail. An important aspect of this work is that the use of XPS and TOFSIMS to analyze electrodeposited silane films provided direct evidence for the presence of O₂Al(O–Si–O) and OAl(O–Si–O)₂ groups at the silane–aluminum oxide interface. Such bonds have been suggested, but they have largely remained elusive over the years.     

铝合金表面新型硅烷膜的制备及表面形貌研究

通过正交试验确定了铝合金表面硅烷膜技术的最佳工艺参数。在基础配方上制备了硅烷膜,利用硫酸铜点滴试验评价了工艺参数,结果表明,水解温度、硅烷浓度、醇水比及pH主要影响了硅烷溶液的水解与缩合反应。分析了硅烷膜的表面形貌、初步探讨了硅烷膜的耐腐蚀性能,结果表明,硅烷膜均匀、致密,具有比铬酸盐钝化更优的防护作用。     

Deposition of hybrid 3-GPTMS's film on AA2024-T3: Dependence of film morphology and protectiveness performance on coating conditions

This paper describes the elaboration of 3-glycidoxypropyltrimethoxysilane (3-GPTMS) films onto AA2024-T3 aluminum alloy for corrosion protection.The dependence of sol–gel morphology on both precipitation under cathodic polarization and nitrate incorporation was investigated via scanning electron microscopy (SEM).Once added into silanization solution, sodium nitrate promoted the reaction of silane condensation and enhanced the film compactness.Electrochemical impedance spectroscopy results (EIS) indicated that doping silane film with NaNO₃ ameliorated its barrier property and protectiveness. Silane films applied onto AA2024-T3 surface by using potentiostatic method, exhibited obviously higher corrosion resistance than those obtained by conventional “dip-coating” method. The resistance of coating is accentuated when not very negative potential was applied.     

Adhesion aspects of poly(p-xylylene) to SiO2 surfaces using γ-methacryloxypropyltrimethoxysilane as an adhesion promoter

The use of organo-silanes as coupling agents offers the potential to create novel structures using materials that would otherwise suffer from poor adhesion. γ-methacryloxypropyltrimethoxysilane (γ-MAPTS) layers were deposited on hydroxylated SiO₂ surfaces using both vapor and solution deposition techniques. The films were characterized using variable angle spectroscopic ellipsometry, infrared spectroscopy, contact-angle measurements and X-ray photoelectron spectroscopy. Film thickness was relatively constant at ～6 Å for solution deposition times from 2 min to 2 h at 60° C. Water contact angle increased from 0° to 45° after silane deposition from solution. Room temperature vapor-deposited γ-MAPTS films showed similar thicknesses to those of solution deposited films but a markedly lower contact angle of 10°. Parylene N was chemical vapor deposited on the γ-MAPTS films and its adhesion was tested using the Scotch^® Tape test. The γ-MAPTS improved adhesion of parylene N to the hydroxylated surface, with the adhesion for the vapor deposited silane films exhibiting a temperature and time dependence.     

Electroformed iron and FeCo alloy

Iron and FeCo alloys were electroformed from additive-free acidic chloride baths. Film stress and magnetic properties were strongly influenced by deposition current density and operating temperature. In general, low film stress and low coercivity (H_C) was achieved with low current density and high operating temperature baths. SEM micrographs indicated that these conditions promote large grain growth. Coercivity of electroformed iron films linearly increased with increasing film stress, indicating that magnetoelastic energy is a dominant anisotropy. The addition of 0.25 M CaCl₂ improves current efficiency while maintaining low film stress. The lowest iron film stress of 5 MPa was achieved from 1.5 M FeCl₂ in the absence of CaCl₂ at 20 mA cm⁻² with a current efficiency of 91%. A “normal” codeposition of FeCo was observed in acidic chloride baths, where the deposition rate of Co²⁺ was faster than Fe²⁺. Film compositions also played an important role in magnetic properties of FeCo films in addition to film stress. Magnetic saturation (M_S) of FeCo films increased linearly with an increase in deposited Fe content. High magnetic saturation with low-stress (M_S of 2.3 T and σ=70 MPa) were achieved from 71Fe29Co films.     

Transparent silica thin films prepared from sodium silicate and bovine serum albumin with petal effect

A variety of advanced functions such as hydrophilicity and hydrophobicity are required for transparent glass plates recently. This paper reports a new procedure to produce transparent silica thin films on glass plates obtained from sodium silicate as inexpensive silica source by its dip coating and subsequent deposition of silica with (NH₄)₂SO₄ solution. When the thin films were prepared using bovine serum albumin (BSA), the resulting transparent films became more hydrophobic than that obtained without BSA and had good adhesion with water droplet, the so-called “petal effect”. Water droplet on the silica thin film did not slide down even when the substrate turned vertically and upside down. Although no BSA was included in the silica thin film, BSA contributed to the formation of nano-sized asperity structures in the film, producing more hydrophobic (less hydrophilic) property and the petal effect.     

pH-controllable bioelectrocatalysis of glucose by glucose oxidase loaded in weak polyelectrolyte layer-by-layer films with ferrocene derivative as mediator

Oppositely charged poly(allylamine hydrochloride) (PAH) and hyaluronic acid (HA) were assembled into {PAH/HA}_n layer-by-layer (LBL) films on pyrolytic graphite (PG) electrodes. Glucose oxidase (GOD) in solution was then loaded into the films, designated as {PAH/HA}_n-GOD. When the {PAH/HA}_n-GOD film electrodes were placed in pH 5.0 buffers containing ferrocenedicarboxylic acid (Fc(COOH)₂) and glucose, a well-defined and large cyclic voltammetric (CV) oxidation wave of glucose catalyzed by GOD immobilized in the films and mediated by Fc(COOH)₂ in solution was observed. However, when the films were placed in pH 9.0 buffers containing the same amount of Fc(COOH)₂ and glucose, the electrocatalytic response was quite small. The bioelectrocatalysis for the film system was at the “on” state at pH 5.0 and at the “off” state at pH 9.0. This pH-sensitive “on-off” behavior was reversible and could be repeated for several times. The possible mechanism of the pH-switchable bioelectrocatalysis was explored and discussed, and should be mainly attributed to the different electrostatic interaction between Fc(COOH)₂ and the films at different pH. This work provides a novel model to realize pH-controllable bioelectrocatalysis based on the enzyme-loaded LBL assembly films, and may guide us to develop the tunable electrochemical biosensors based on electrocatalysis with immobilized enzymes.     

Electro-assisted preparation of dodecyltrimethoxysilane/TiO2 composite films for corrosion protection of AA2024-T3 (aluminum alloy)

Thin films of organosilanes have been successfully used as the alternative to toxic chromate coatings for surface pretreatment of metals and alloys. To further improve their corrosion performance, in the present work nano-scaled TiO₂ particles were added to the dodecyltrimethoxysilane (DTMS) films coated onto AA2024-T3 substrates, by using either the dip-coating or the cathodically electro-assisted deposition process. The obtained composite films were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle measurements, Fourier transform reflection-absorption IR (FTRA-IR) and electrochemical impedance spectroscopy (EIS). The results show that these two techniques (nanoparticles incorporation and the electro-assisted deposition) both facilitate the deposition process of silane films, giving thicker deposit and higher coverage surface along with higher roughness and hydrophobicity, and thereby improve their corrosion resistance. Moreover, the corrosion performance of silane films is further improved by the combined use of nanoparticles modification and electro-assisted deposition.     

助溶剂对铝合金表面硅烷化预处理的影响

为了了解3-缩水甘油醚丙基三甲氧基硅烷(γ-GPTMS)溶液中助溶剂对水解的γ-GPTMS在铝合金表面的沉积特性的影响,用X射线光电子衍射(XPS)测定了不同助溶剂含量,不同γ-GPTMS浓度的溶液沉积在铝合金表面的硅含量,同时用反射吸收红外光谱(RAIRS)对铝合金表面膜层进行了表征,结果表明,助溶剂对γ-GPTMS在铝合金表面沉积有显著影晌,γ-GPTMS的纯水溶液在铝合金表面所形成硅烷化膜层的硅元素量最高,沉积量随溶液中γ-GPTMS浓度的增加而增加。另外,膜层与氧化的铝合金表面之间形成铝硅氧烷(Al-O-Si)共价键,而且γ-GPTMS分子中的烷氧乙基分布在膜层的外表面,具有较大的反应活性。     

AFM study of the vinyl triethoxysilane (A-151) film prepared by spraying deposition and dipping deposition

The vinyl triethoxysilane (A-151) film was prepared by the spraying deposition and dipping deposition technique. The surface topography and growth behavior of A-151 films was investigated by using atomic force microscopy (AFM) and static water contact angle measurements. The results indicate that the topography was strongly affected by the treatment conditions. The surface topography of silane film was changed from the islands morphology to the network morphology with the increasing temperature of SiO₂ substrate, and the larger self-polymerized silane aggregation will be formed by using the ultrasonic technology. The hydrophobicity of the SiO₂ substrate was improved after A-151 deposition.     

Preparation and characteristics of a waterborne preventive stain coating material with organic-inorganic composites

With the goal of developing a waterborne coating material that prevents staining, organic-inorganic composites prepared from colloidal silica and two types of acrylic resin emulsions were investigated as exterior coatings. conventional acrylic resin emulsion and organic silane hybridized acrylic resin emulsion prepared by emulsion polymerization were mixed with colloidal silica to form organic-inorganic comiposite films. The addition of colloidal silica to emulsions yielded films with higher hydrophilicities, as indicated by lower water contact angles for these films in comparison to films without colloidal silica. The water contact angles of organic silane hybridized acrylic resin emulsion/colloidal silica films were lower than those of acrylic resin emulsion/colloidal silica films. Composite films containing colloidal silica particles smaller than 100 nm in diameter showed high hydrophilicities. Observations of the dispersed state of colloidal silicaparticles in organic-inorganic composite films by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that colloidal silica particles were densely aggregated on the film surface. Outdoor exposure tests of the coating materials prepared from organic silane hybridized acrylic resin and colloidal silica particles with diameters of 7.5 nm showed excellent stain resistance.     

Properties of organic–inorganic composite materials prepared from acrylic resin emulsions and colloidal silicas

To design an organic–inorganic composite material with colloidal silica as the inorganic component, an acrylic resin emulsion and an organic silane hybridized acrylic resin emulsion were prepared by emulsion polymerization. The organic–inorganic composite films were prepared by blending the emulsion and the colloidal silica. The contact angles for water, gloss at 60°, and the transparencies of those films were measured. The dispersion state of colloidal silica in films was observed with a scanning electron microscope (SEM) and a transmission electron microscope (TEM). From these results, the contact angle for water of the organic–inorganic composite film obtained from the silane hybridized acrylic resin emulsion was lower than that of the organic–inorganic composite film obtained from an acrylic resin emulsion. The contact angles for water in organic–inorganic composite films with colloidal silicas were lower than those of the films without the colloidal silicas. The films prepared from silane hybridized acrylic resin emulsion composites with colloidal silicas of less than 100 nm were more hydrophilic. SEM and TEM observations demonstrated that some aggregations of the small colloidal particle silica were densely dispersed on the film surface. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2051–2056, 2006     

Enabling a commercial computational fluid dynamics code to perform certain nonlinear analysis tasks

In this work we enable the commercial computational fluid dynamics code Fluent, to successfully trace a complete solution branch, even past turning points. Here the so-called Recursive Projection Method (RPM) is implemented as a computational shell “wrapped” around Fluent, in conjunction with a pseudo-arc-length method for convergence on the unstable branch. The case study is a mixed convection flow in a stagnation point chemical vapor deposition (CVD) reactor. Multiple steady states coexist over a range of inlet Reynolds numbers, due to the competition of the two dominant physical mechanisms: forced and free convection. Continuation on the solution branch reveals a curve consisting of a stable branch, dominated by free convection, followed, past the first turning point, by an unstable branch. Past a second turning point, follows another stable branch dominated by forced convection. Taking the problem a step further, it is augmented with a chemical model describing the deposition of silicon (Si) from silane (SiH₄), silylene (SiH₂) and hydrogen (H₂). The solution branch does not alter since the gas mixture is dilute and the carrier gas, in this case nitrogen (N₂), and the precursor, in this case SiH₄, are of similar molar masses; the concentration differences cannot lead to solutal convection. Results for the mass fraction distribution inside the reactor and the film growth rates are reported in all parts of the solution branch.     

Thickness-dependent crystal orientation in poly(trimethylene 2,6-naphthalate) films studied with GIWAXD and RA-FTIR methods

The thickness dependence of the crystal orientation of poly(trimethylene 2,6-naphthalate) (PTN) films was clearly demonstrated using the methods of two-dimensional grazing incidence wide angle X-ray diffraction (2D GIWAXD) and grazing incidence reflection absorption FTIR (RA-FTIR) spectroscopy. The 2D GIWAXD results showed that for films thicker than 200 nm, the “c” axis (main chain direction) and “b” axis of crystal unit cell are almost parallel to the sample surface, whereas for thin films the “c” axis is preferentially perpendicular to the film plane in the crystalline phase of isothermally crystallized PTN films. The anisotropic orientation of the naphthalene rings in the isothermally crystallized PTN film was also confirmed. By analyzing the relative absorbance of the parallel band (1602 cm⁻¹) to the one of perpendicular band (917 cm⁻¹), the thickness dependence of the crystal orientation suggested by the GIWAXD results was also confirmed. Furthermore, the naphthalene rings in the isothermally crystallized thick films were found to lie flat on the film plane. The chain orientations derived from the GIWAXD and RA-FTIR results in this work were found to be consistent with the “flat-on” and “edge-on” lamellar orientation for the thin and thick films, respectively, which has previously been reported in many polymer systems.     

Optimal parameters to produce high quality diamond films on 3D Porous Titanium substrates

Diamond films grown on three-dimensional (3D) porous titanium substrate were obtained by hot filament chemical vapor deposition (HFCVD) technique. The growth parameters strongly influenced the film properties during this complex film formation process. The pressure inside the reactor as well as the methane concentration showed their influence on the film morphology, quality, and growth rate. The substrates were totally covered by a diamond coating including deeper planes leading to a 3D porous diamond/Ti composite material formation. The sp²/sp³ ratio as “purity index” (PI) and the “growth tendency index” (GTI), evaluated from Raman and X-ray spectra respectively, were obtained for these composite materials as a function of their growth parameters.     

Electrochemical investigation of high-performance silane sol–gel films containing clay nanoparticles

Silane sol–gel coatings are widely used as adhesion promoters between inorganic substrates, such as metals, and organic coatings. The aim of these pre-treatments is to enhance the corrosion protection performance of the organic coating improving the adhesion to the substrate and acting as a barrier against water and aggressive ions diffusion. It is a matter of fact that the silane sol–gel pre-treatments do not provide an active protection against corrosion processes except for the partial inhibition of the cathodic reaction. Inorganic pigments can improve the barrier properties of the silane sol–gel film, enhancing the resistance against corrosion. In this study, different amounts of montmorillonite nanoparticles were added to a water based silanes mixture in order to improve the barrier properties of the sol–gel coating. Hot dip galvanized steel was used as substrate. The sol–gel film consists of a combination of three different silanes, GPS, TEOS and MTES. The clay nanoparticles used in this study were mainly neat montmorillonite. The proper concentration of filler inside the sol–gel films was determined comparing the corrosion resistance of silane layers with different nanoparticles contents. Additionally, the effect of CeO₂ and Ce₂O₃ enriched montmorillonite particles. The EIS analysis and the polarization measurements demonstrated that the optimal amount of neat montmorillonite nanoparticles is about 1000 ppm. The same electrochemical techniques highlighted the limited effect of the cerium oxides grafted to the clay nanoparticles on the corrosion resistance of the silane sol–gel film. The TEM analysis proved the presence of a nano-crystalline structure inside the silane sol–gel film due to the formation of crystalline silica domains.     

Nanocoating hybrid polymer films on large quantities of cohesive nanoparticles by molecular layer deposition

The conformal coating of ultra‐thin aluminum alkoxide (alucone) polymer films on primary silica and titania nanoparticles using molecular layer deposition (MLD) in a fluidized bed reactor from 100 to 160 °C is described. In situ mass spectrometry revealed that the growth of alucone MLD films was self‐limiting as a function of the individual trimethylaluminum and ethylene glycol exposures. The composition and highly conformal alucone films throughout the surface of both silica and titania nanoparticles were confirmed. The highest growth rate was observed at the lowest sample temperature. Primary nanoparticles were coated individually despite their strong tendency to aggregate during fluidization. Based on the results of chemical and thermogravimetric analysis, the value of x in the formula of Al(OCH₂CH₂O)_x was estimated to be 1.9. The calculated film density slightly increased from 2.0 ± 0.1 to 2.2 ± 0.1 g/cm³ with the increasing of temperature from 100 to 160 °C. © 2009 American Institute of Chemical Engineers AIChE J, 2009