Foam and wetting films from amphiphilic block copolymers: Isoelectric state and stability

Foam and wetting films from PEO-PPO-PEO triblock copolymers Synperonic P85 and F108 are studied under the identical conditions, using microinterference method. The range of background electrolyte concentration, where DLVO (electrostatic and van der Waals) forces and non-DLVO (steric) forces act in the films, is determined. From the dependence of the film thickness on pH, it is unambiguously shown that electrostatic interactions (i.e., the potential and surface charge) in the foam and wetting films caused by the presence of nonionic polymer surfactants arise due to the preferential adsorption of OH⁻ ions at the solution-air interface. The films obtained below the critical pH values are sterically stabilized; i.e., a decrease in pH induces a transition from electrostatic to steric stabilization. Three-layer models are designed for both types of films that allow to calculate electrostatic disjoining pressure Π_el. The values of ϕ₀ potential of the foam film are used to calculate Π_el in wetting films. A relation between the isoelectric state of foam and wetting films and their stability is found to exist in the range of pH corresponding to electrostatic stabilization. Metastable films, film rupture, or the transition to sterically stabilized films were also found. The text was submitted by the authors in English.     

Electrochemical charging and electrocatalysis at hybrid films of polymer-interconnected polyoxometallate-stabilized carbon submicroparticles

Using the layer-by-layer technique, carbon submicroparticles, that have been modified and stabilized with monolayers of Keggin-type phosphododecamolybdate (PMo₁₂O₄₀³⁻), can be dispersed in multilayer films of organic polymers, poly(3,4-ethylenedioxythiophene), i.e., PEDOT, or poly(diallyldimethylammonium) chloride, i.e., PDDA, deposited on glassy carbon or indium-tin oxide conductive glass electrodes. The approach involves alternate treatments in the colloidal suspension of PMo₁₂O₄₀³⁻-covered carbon submicroparticles in the solution of monomer, 3,4-ethylenedioxythiophene or in solution of PDDA polymer. Electrostatic attractive interactions between anionic phosphomolybdate-modified carbon submicroparticles and cationic polymer layers permit not only uniform and controlled growth of the hybrid organic–inorganic film but also contribute to its overall stability. The system composed of PMo₁₂O₄₀³⁻-covered carbon submicroparticles dispersed in PEDOT is characterized by fast dynamics of charge transport and has been used to construct symmetric microelectrochemical redox capacitor. The PDDA-based system has occurred to be attractive for electrocatalytic reduction of hydrogen peroxide.     

Interaction between a stationary mercury electrode and a hydrogen bubble in an aqueous sodium dodecyl sulphate solution

The stability and rupture of thin liquid films formed from an aqueous solution of Na₂SO₄ (0.05 mol dm⁻³) in the presence of 5 × 10⁻⁵ mol dm⁻³ sodium dodecyl sulphate between a stationary mercury electrode and a hydrogen bubble has been investigated as a function of electrode potential. The electrostatic component of disjoining pressure has been calculated using the results of capacity measurement for the mercury-solution interface. Special attention has been paid to films formed on positively charged mercury surfaces. In this case, despite the positive electrode polarization, the outer Helmholtz plane potential is found to be negative due to the high surface activity of the dodecyl sulphate anion. The van der Waals component of disjoining pressure has been calculated on the basis of a double sheath model of the two interacting surfaces, taking into consideration the orientation of the adsorbed surfactant layers at the interfaces. Calculations of the total disjoining pressure can explain film stability at negative mercury potentials, but do not explain film rupture when the polarization of the mercury is positive. The existence of a hydrophobic attractive interaction is postulated in the latter case.     

Investigations on poly(methyl methacrylate)-poly(ethylene oxide) hybrid polymer electrolytes with dioctyl phthalate, dimethyl phthalate and diethyl phthalate as plasticizers

Plasticizers can be used to change the mechanical and electrical properties of polymer electrolytes by reducing the degree of crystallinity and lowering the glass transition temperature. The transport properties of gel-type ionic conducting membranes consisting of poly(ethylene oxide) (PEO), poly(methyl methacrylate) (PMMA), LiClO₄ and dioctyl phthalate, diethyl phthalate or dimethyl phthalate (DMP) are studied. The polymer films are characterized by X-ray diffraction, Fourier transform infrared and impedance spectroscopic studies. It is found that the addition of DMP as the plasticizer in the PEO-PMMA-LiClO₄ polymer complex favours an enhancement in ionic conductivity. The maximum conductivity value obtained for the solid polymer electrolyte film at 305 K is 3.529×10^{– 4} S cm^–1. Electronic Publication     

Evolution of an iron passive film in a borate buffer solution (pH 8.4)

The evolution under open-circuit conditions of iron passive films formed at 0.8 V_SCE in a borate buffer solution at pH 8.4 was investigated with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The composition of the freshly formed passive film as determined by X-ray photoelectron spectroscopy (XPS) was found to be in agreement with a bilayer model, where the inner layer is composed mainly of iron oxide and the outer layer consists of a hydrated material. Results of XPS measurements also showed that the open-circuit breakdown of passive films was consistent with a reductive dissolution mechanism. When the iron electrode reached an intermediate stage in the open-circuit potential decay (approximately −0.3 V_SCE), the oxide film, containing both Fe(II) and Fe(III), was still protective. The impedance response in this stage exhibited a mixed control by charge transfer at the metal/film and film/solution interfaces and diffusion of point defects through the film. At the final stage of the open-circuit potential decay (approximately −0.7 V_SCE), the oxide film was very thin, and the ratio of Fe³⁺/Fe²⁺ and O²⁻/OH⁻ had decreased significantly. The impedance response also exhibited a mixed charge-transfer–diffusion control, but the diffusion process was related to transport of species in the electrolyte solution resulting from dissolution of the oxide film.     

纳米TiO2介孔薄膜的模板组装制备研究

以TiCl₄为无机前驱体、三嵌段高分子共聚物EO₂₀PO₇₀EO₂₀为模板剂，在非水条件下制备了有序的锐钛矿TiO₂纳米晶介孔薄膜。通过热重-差热（TG-DTA）分析、X射线衍射（XRD）分析、原子力显微观察（AFM）及N₂吸附-脱附等测试对样品进行了表征。结果表明，薄膜具有均一的大介孔孔径（～10 nm），其BET比表面积为150 m²·g^-1，薄膜较宽的无机壁厚显著提高了介孔结构的热稳定性。通过红外（IR）光谱分析考察了溶胶-凝胶过程中发生的物理化学变化。在对薄膜表面形貌进行AFM观察的基础上初步探讨了嵌段共聚物EO₂₀PO₇₀EO₂₀对薄膜孔结构形成的导向机理。     

还原石墨/氧化锌复合薄膜的制备及其光电转换性能

本工作研究不同过程还原的氧化石墨rGO/ZnO(reduced graphiteoxide/ZnO)复合膜的可见光激发光电转换性能。氧化石墨(GO)经KOH还原处理或NaBH4还原处理后,和氧化锌溶胶混合,通过旋涂法和热处理在F掺杂SnO2薄膜导电玻璃(FTO)衬底上形成复合薄膜。采用XRD、FTIR、FE-SEM、XPS、UV-Vis等方法对复合薄膜的晶相结构、微观形貌等进行表征,并测试了复合薄膜在可见光照射下的光电转换性能。GO的预处理过程对复合薄膜的结构影响显著,采用NaBH4对GO处理更有利于形成均匀薄膜。光电流测试结果表明不同复合薄膜均能实现可见光照射下产生光电流,其原理为rGO的光激发电子跃迁到ZnO,而空穴在rGO中迁移,在rGO与ZnO界面实现光生载流子分离。其中NaBH4处理后的rGO/ZnO复合薄膜光电流密度最大,达6×10-7A·cm-2。     

Effects of molecular weight of nitrocellulose on structure and properties of polyurethane/nitrocellulose IPNs

Semi‐interpenetrating polymer network (semi‐IPN) coatings were prepared by using castor oil‐based polyurethane (PU) and nitrocellulose (NC) with various viscosity‐average molecular weights (M_η) from 6 × 10⁴ to 42 × 10⁴, and coated on a regenerated cellulose (RC) film to obtain water‐resistant film. The PU/NC coatings and coated films, which were cured at 80°C for 5 min and 2 min, respectively, were investigated by infrared (IR) and ultraviolet (UV) spectroscopy, X‐ray diffraction, swelling test, strength test, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results show that the crosslink densities of the PU/NC semi‐IPNs were smaller than that of pure PU, and decreased with the decrease of M_η of nitrocellulose (NC M_η), indicating NC molecules cohered intimately with PU, and hindered the PU network formation. The physical and mechanical properties of the films coated with PU/NC coatings were significantly improved. With the increase of NC M_η, the strength and thermal stability of the coated films increased, but the pliability, water resistivity, and optical transmission decreased slowly. The PU/NC coating with low NC M_η more readily penetrated into the RC film, and reacted with cellulose, resulting in a strong interfacial bonding and dense surface caused by intimate blend of PU/NC in the coated films. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1623–1631, 1999     

Synthesis of platinum colloids sterically stabilized by poly(N-vinylformamide) or poly(N-vinylalkylamide) and their stability towards salt

Colloidal dispersions of nanometer-sized platinum colloids were prepared by ethanol reduction of PtCl₆ ²⁻ in the presence of poly(N-vinylformamide) (PNVF), poly(N-vinylacetamide) (PNVA) or poly(N-vinylisobutyramide) (PNVIBA) and analyzed by UV-vis spectroscopy and transmission electron microscopy. The dispersion stability of each colloid to the presence of added KCl was determined by a stirring and centrifugation procedure. The platinum colloid stabilized by PNVF (PNVF-Pt) was the most stable and its critical flocculation concentration was not observed up to the highest electrolyte concentration employed (4.0 M). The stability of the platinum colloids stabilized by poly(N-isopropylacrylamide) (PNIPAAm) and poly(vinylpyrrolidone) (PVP) was also examined. The sequence of polymer-stabilized platinum colloids in increasing order of dispersion stability was found to be PNIPAAm-Pt < PNVIBA-Pt < PVP-Pt < PNVA-Pt < PNVF-Pt. Received: 25 August 1998 Accepted in revised form: 14 January 1999     

Oxygen evolution: the mechanism of formation of porous anodic alumina

Abstract  Aluminium anodization behavior in ammonium sebacate solution (w = 4%) in ethylene glycol, and in several H₃PO₄-containing electrolytes, has been investigated. A new mechanism is proposed for the formation of porous anodic films. The model emphasizes the close relationship between pore generation and oxygen evolution. PO₄ ³⁻ ions incorporated in the anodic films behave as the primary source of avalanche electrons. It is the avalanche electronic current through the barrier film that causes oxygen evolution during anodization. When growth of anodic oxide and oxygen evolution occur simultaneously at the aluminium anode, cavities or pores are formed in the resulting films. Accordingly, the mechanisms of growth of barrier and porous films are not very different in nature. These findings are a decisive new step towards full understanding of the nature of anodic alumina films. Graphical abstract        

Electrochemical preparation of poly(<Emphasis Type="Italic">p</Emphasis>-phenylene) thin films

We report the electrochemical preparation of poly(p-phenylene) (PPP) thin films with a polymerization degree of approximately 20 using biphenyl as starting material. The PPP films are prepared directly on a tin oxide electrode, presenting a positive charge carrier mobility of 5×10⁻⁷ cm² V⁻¹ s⁻¹.     

Electrochemical kinetics of nanosized Ag and Ag2O thin films prepared by radio frequency magnetron sputtering

Ag and Ag₂O thin films have been prepared by radio frequency magnetron sputtering on Cu substrates and have been characterized by X-ray diffraction, scanning electron microscope and atomic force microscope. The electrochemical performance of the thin films has been studied by galvanostatic cycling and cyclic voltammetry. The potential dependence of Li-ion chemical diffusion coefficients, [(D)\tilde]_\textLi {\widetilde{D}_{\text{Li}}} , of the films has been determined by galvanostatic intermittent titration technique and electrochemical impedance spectroscopy. It is found that Li-ion chemical diffusion coefficients of the Ag film range from 10⁻¹⁶ to 3 × 10⁻¹⁴ cm² s⁻¹. The Ag/Li₂O composite that is formed from Ag₂O after the first cycle exhibits higher [(D)\tilde]_\textLi {\widetilde{D}_{\text{Li}}} values than the Ag film, especially at a low Li-intercalation content. The phase transitions in the two-phase region cause a significant decrease of chemical diffusion coefficients.     

Preparation and dielectric properties of highly preferred-(100) orientation (Pb,La)(Zr,Ti)O<Subscript>3</Subscript> antiferroelectric thick films by sol–gel processing

Pb_0.97La_0.02Zr_0.95Ti_0.05O₃ (PLZT) antiferroelectric thick films of highly preferred-(100) orientation with different thickness were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates depending on the sol–gel process technique. The effects of the PLZT thick films in the preparation and electric properties are investigated. The films show polycrystalline perovskite structure with a (100) preferred orientation by X-ray diffractometer analyses. The antiferroelectric nature of the thick films is demonstrated by P (polarization)–E (electric field). The temperature dependence of the dielectric constant and dielectric loss displays the similar behavior in both cases at 100 kHz while the values of polarization characteristic are decreased with the increase of the film thickness. The phase switching current are studied as a function of a gradually change dc electric field and the voltage dependent current density of the most highly (100)-oriented PLZT film is 1.49 × 10⁻⁸ A/cm² over electric field range from 0 to ±261 kV/cm. The film at 2,498 nm exhibits excellent dielectric properties and highly preferred-(100) orientation.     

Electrical characterization of poly(3-methylthiophene) electrosynthesized onto a tin-oxide substrate

We have investigated poly(3-methylthiophene) (PMeT) thin films electrochemically synthesized directly onto a tin-oxide (TO) electrode. We find that the PMeT film thickness depends linearly on the charge density used during the electropolymerization. We have demonstrated that the current transport in PMeT films (solid phase) is space-charge limited or controlled by thermionic emission, depending on the electrode material. Using TO/PMeT/Ni devices we estimate the positive charge carrier mobility in PMeT to be around 4 × 10⁻⁴ cm² V⁻¹ s⁻¹, and the potential barrier height for positive charge carrier injection at the Al/PMeT interface to be 0.17 eV. Received: 6 December 1999 / Accepted: 24 February 2000     

Determination of Nitrite by a Modified Electrode of Poly(1-Naphthylamine) Film Doped with Dawson-Type Heteropolyanions

 The voltammetric behavior of the electrode modified with poly(1-naphthylamine) film doped with α-P₂W₁₈ heteropolyanions was investigated. The concentration of the modifier, the acidity of the medium and the scan range of potential had obvious effects on the electrochemical characteristics of the electrode. The electrocatalytical characteristics of the film electrode were studied by cyclic voltammetry and other methods. It is suggested that the electrocatalytic reaction of nitrite is controlled by its diffusion. The applicability of the electrode was assessed by the determination of nitrite in waste-water. Determination limit for nitrite was 5 × 10⁻⁷ mol.L⁻¹. Received August 23, 1999. Revision January 2, 2001     

Structural and Optical Properties of Sol-Gel Deposited Proton Conducting Ta2O5 Films

Proton conducting tantalum oxide films were deposited on ITO (Indium Tin Oxide) coated glass, fused silica and soda-lime glass substrates by spin coating using a sol-gel process. The coating solutions were prepared using Ta(OC₂H₅)₅ as a precursor. X-ray diffraction studies determined that the sol-gel films, heat treated at temperatures below 400°C, were amorphous. Films heat treated at higher temperatures were crystalline with the hexagonal δ-Ta₂O₅ structure. The solar transmission values (T _s ) of tantala films on glass generally range from 0.8–0.9, depending on thickness. The refractive index and the extinction coefficient were evaluated from transmittance characteristics in the UV-VIS-NIR regions. The refractive index values calculated at λ=550 nm increased fromn=1.78 to 1.97 with increasing heat treatment from 150 to 450°C. The films heat treated at different temperatures showed low absorption, with extinction coefficients of smaller thank=1×10⁻³ in the visible range. Impedance spectroscopic investigations performed on Ta₂O₅ films revealed that these films have a protonic conductivity of 3.2×10⁻⁴S/m. The films are suitable for proton conducting layers in electrochromic (EC) devices.     

Photoelectrochemical properties of indium doped iron oxide

Oxygen photoanodes formed by reactive sputtering of iron oxide onto conducting indium tin oxide (ITO) substrates held at 350 ° C have been investigated by conventional photoelectrochemical, impedance, XPS and auger spectroscopic methods. This fabrication procedure leads to films containing 8 to 20 atomic % indium in the front portion of the film, increasing to much higher values near the ITO interface (back portion of the film). Two interesting effects are observed with the thin-film iron oxide formed in this way. The first is that the as formed films must be vacuum annealed before an appreciable dc photoanodic response is observed. Secondly, films 250 nm thick display the property of giving about double the quantum yield for back face, than for front face, illumination over the spin and parity forbidden transition centered at 535 nm. On correcting for transmission and reflection losses, the resulting true quantum efficiencies satisfy the same inequality, a result that can only be accounted for by a higher ( > 2 × ) primary quantum efficiency for the back, versus the front portion of the film. As these films show substantially higher quantum efficiencies than do indium free films of the same thickness, it is concluded that the indium in the films is responsible for the increase in primary quantum efficiency. This result is discussed in terms of a localized states model for α-Fe₂O₃.     

Electron transfer reaction of electrochemically polymerized tris-(amino-phenanthroline)-iron(II/III) complex films

New films of iron complex with 4,7-bis(2-aminophenyl)-methylaminosulfonylphenyl)-1,10-phenanthroline (APP) and 5-amino-1,10-phenanthroline (AP) are prepared on the electrode surface of In–Sn oxide conducting glass (ITO) by electrochemical oxidation. The thickness (Φ) of the films prepared on the ITO can be controlled by the number of cycles of the potential scan. The resulting film-coated electrodes show well-defined reversible vol-tammograms corresponding to the redox reaction of the Fe(II/III) complexes in 0.1 M NaClO₄ acetonitrile (AN), a mixture of butylene carbonate (BC) and propylene carbonate (PC) and poly2-hydroxyethylmethacrylate gel containing BC and PC. The electron transfer processes within the films can be treated apparently as diffusional processes characterized by the rate constants of the apparent diffusion coefficient (D_app). The value of D_app increase from 1.0 × 10^?9 to 1.6 × 10^?8 cm² sec^?1 as the Fe complex concentration (C_Fe) increases from 0.06 to 1.04 M for the [Fe(AP)₃] complex film (Φ=0.80 μm) in 0.2 M NaClO₄/AN solution. The D_app value for the [Fe(APP)₃) complex film (C_Fe = 0.19 M , Φ= 0.78 μm) is 3.5 × 10^?9 cm² sec^?1 in 0.2 M NaClO₄/AN solution. The D_app values of the [Fe(AP)₃] complex film in the PC + BC mixture and gel containing 1.0 M NaClO₄ were smaller than those obtained in AN solution by an order of magnitude. The dependence of the apparent formal potential of the Fe(II/III) redox reaction for the [Fe(AP)₃] complex film on the activity of NaClO₄ supporting electrolyte in AN shows that Na⁺ moves preferentially across the polymer/solution interfaces during the redox reaction. The Fe(II/III) redox reaction of the Fe complex films shows reversible electrochromic response between red and colorless.     

Liquid crystalline main chain polymers with a poly(p-phenylene-terephthalate) backbone: 7. Thermal expansion of oriented films of the polyester with dodecyloxy side chains

The linear thermal expansion coefficients of oriented films of poly(p-phenylene-2,5-didodecyloxy-terephthalate) in the three structures B, A, and L_f are reported. The results are interpreted in terms of a molecular laminate model in which the rigid main-chain layers are separated by the aliphatic side chains. In a film oriented unidirectionally the rigid mainchain layers provide a negative contribution to the thermal expansion coefficient, while the side chains supply a positive contribution. Therefore, the resulting expansion coefficient α depends on the details of the main- and side-chain packing and low-temperature values between α = +0.3 × 10^?5 K^?1 (A and L_f and α = ?1.2 × 10^?5 K^?1 (B) are found in highly oriented films. Measurements on undrawn films are in accordance with the molecular laminate model. © 1994 John Wiley & Sons, Inc.     

Modifiying glassy carbon electrode with ferrocene-bridged polysilsesquioxanes

Ferrocene-bridged polysilsesquioxanes film electrodes were prepared via depositing the sols formed by hydrolysis of 1,1′-bis[(2-triethoxylsilyl)ethyl]ferrocene (BTEF) or co-hydrolysis of poly(vinylalcohol) (PVA) with BTEF or tetraethoxysilane (TEOS) with BTEF onto glassy carbon electrode (GCE) surface. The electrochemical behavior of the modified electrodes were characterized by cyclic voltammogram (CV) in aqueous solution. The BTEF film, BTEF/PVA film and BTEF/TEOS film all exhibit a redox wave at E^0’ are 0.504, 0.326, 0.318 V, with the peak potential separation (ΔE) are 0.132, 0.042, 0.028 V, and the value of i_pa/i_pc are 1.8097, 1.007, 1.064 (vs. SCE), respectively. This suggests that BTEF/PVA film and BTEF/TEOS film have a good reversible redox behavior and the redox peak is corresponded to a one-electron reduction and oxidation process. After successive 50 time’s cyclic voltammetric, there is no peak potential shift, and the peak current only decreased 5.58, 4.95%, respectively. BTEF/PVA film has better hydrophilicity and shows a more perfect electrocatalytic activity in the oxidation of H₂A than that of the BTEF/TEOS film. The catalytic peak current has a linear relationship with the concentration of H₂A in the range of 1.0 × 10⁻⁵~1.0 × 10⁻³ M.