Isoelectric state and stability of foam films, bubbles and foams from PEO–PPO–PEO triblock copolymer (P85)

Influence of pH of P85 copolymer solutions on stability of microscopic foam films (static conditions), lifetime of single bubbles at solution surface (quasi-static conditions), volume of the foam formed (dynamic conditions) and time of rupture of the foam column was investigated. Variations of the film equilibrium thickness as a function of pH were determined for different ionic strengths of the solutions using microinferometric method, while the combined pneumatic–mechanical method was applied in experiments on foams. It was found that lowering the pH reduced stability of the foam films, and at lower ionic strength the films ruptured at pH 2.9 (isoelectric point). Simultaneously, the lifetime of single bubbles was much shorter at lower pH of the P85 solutions. The average life, t _av, was 11.1 s at pH 5.8, while at pH 3.0, only 3.1 s. Under dynamic conditions the pH lowering did not significantly influence the solution foamability.     

TiO2 Thin Film with Varied Porous Structure Applied on the Degradation of Methylene Blue

In this study, porous TiO₂ thin films were prepared by the sol‐gel method employing polyethylene glycol 1000 (PEG 1000) as an organic template. Pore sizes were adjusted by varying the concentration of PEG 1000. The optimal PEG concentration range required to form TiO₂ films with a regular porous structure was investigated and was found to be 0.01–0.015 M. As the PEG 1000 concentration increased, the surface of these films became rougher because of larger pores. Degradation of methylene blue (MB) under UV irradiation was used to determine the photocatalytic activity of the films. In addition, the effect of the pH value of the MB solution on the films was evaluated by controlling its pH value at 5, 7, and 9. The results showed that the photocatalytic activity was correlated to the pore size and pore density of the thin films. TiO2 thin films possessing pore sizes in the diameter range of 35–85 nm exhibited the best conversion of 98% after 8 h of UV irradiation when the pH value was 7.     

Bioinert solution-cross-linked hydrogen-bonded multilayers on colloidal particles

Bioinert polyelectrolyte multilayers comprised of poly(acrylic acid) and polyacrylamide were deposited on colloidal particles (1.7 microm in diameter) at low pH conditions by layer-by-layer assembly using hydrogen-bonding interactions. The multilayer films were coated uniformly on the colloidal particles without causing any flocculation of the colloids, and the deposited films were subsequently cross-linked by a single treatment of a carbodiimide aqueous solution. The lightly cross-linked multilayer films show excellent stability at physiological conditions (pH 7.4, phosphate-buffered saline), whereas untreated multilayer films dissolved. The multilayer-coated surfaces, both on flat substrates and on colloidal particles, exhibit excellent resistance toward mammalian cell adhesion. With this new solution-based cross-linking method, bioinert H-bonded multilayer coatings offer potential for biomedical applications.     

pH sensor based on polyaniline and aniline–anthranilic acid copolymer films using quartz crystal microbalance and electronic absorption spectroscopy

The pH sensitivity based on conducting polyaniline (PANI) and copolymer of aniline and o‐anthranilic acid (AA) films were studied using quartz crystal microbalance (QCM) technique and UV–Vis spectroscopy. The sensor was constructed from these polymer films coated on the electrode of the QCM. The resonant frequency changes as a function of pH in the range of 2–12 were measured. These changes are quantitative indication of the degree of dedoping or redoping of the polymer films upon the subsequent exposure of the electrode to 0.25 M sulfuric acid and different pH solutions. There are two linear regressions between the frequency change and pH with two different and opposite slopes in the regions from 2 to 9 and 9 to 12. The pH sensitivity of the copolymer film was found to be less than using the PANI film. Thin films of PANI and copolymer, which were chemically polymerized in a sulfuric acid solution, were deposited onto the inner walls of the quartz cuvettes. The UV–Vis absorption spectra of these films were measured in different pH solutions. Relations between the maximum absorption and its wavelength versus pH were constructed. The copolymer film shows some advantages over the PANI film. The difference between the PANI and copolymer films as pH sensors using the QCM and electronic absorption extends from the determination of pK_a for both films. Copyright © 2008 John Wiley & Sons, Ltd.     

Stimuli‐responsive micelles of amphiphilic AMPS‐b‐AAL copolymers in layer‐by‐layer films

Aqueous reversible addition‐fragmentation chain transfer polymerization was used to synthesize poly(N‐[3‐(dimethylamino)propyl]acrylamide) (PDMAPA) cationic homopolymers and micelle‐forming, pH‐responsive, amphiphilic diblock copolymers of poly(sodium 2‐acrylamido‐2‐methyl‐1‐propanesulfonate‐block‐N‐acryloyl‐L ‐alanine) (P(AMPS‐b‐AAL)). At low pH, the AAL blocks are protonated rendering them hydrophobic, whereas the AMPS blocks remain anionically charged because of the pendant sulfonate groups. Self‐assembly results in core–shell micelles consisting of hydrophobic cores of AAL and negatively charged shells of AMPS. Using solutions of these micelles with anionic coronas and of the cationic homopolymer PDMAPA, layer‐by‐layer (LbL) films were assembled at low pH, maintaining the micelle structures. Several block copolymers with varying AMPS and AAL block lengths were synthesized and used in the formation of LbL films. The thickness and morphology of the films were examined using ellipsometry and atomic force microscopy. The stimuli‐responsive behavior can be triggered by submersion of the film in water at neutral pH to disrupt the micelles. This behavior was monitored by observing the decrease in film thickness and alteration of the film morphology. The micelles were also loaded with a model hydrophobic compound, pyrene, and incorporated into LbL films. The release of pyrene from the films was monitored by fluorescence spectroscopy at varying pH values (1, 3, 5, and 7). As the pH of the solution increases, the rate of release increases. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Hemoglobin adsorption into TiO2 phytate multi-layer films: particle size and conductivity effects

Hemoglobin (molecular weight 64.5 kDa, isoelectric point 7.4) in 0.1 M phosphate buffer solution at pH 5.5 readily adsorbs onto mesoporous TiO₂ phytate films, which have been formed in a layer-by-layer deposition process from TiO₂ nanoparticles (ca. 6–10 nm diameter) and phytic acid at tin-doped indium oxide (ITO) electrodes. Quartz crystal microbalance data, voltammetry, and SEM evidence are consistent with hemoglobin adsorption only into the outer TiO₂ phytate surface layer. The size of the tetrametric hemoglobin protein (ca. 6 nm diameter) appears to be too big for a homogeneous film to form.The modified ITO electrode immersed in 0.1 M phosphate buffer solution at pH 5.5 allows reversible electron transfer for hemoglobin to be observed with a midpoint potential of 0.01 vs. SCE. Characteristic TiO₂ phytate film thickness and pH effects are observed with both thicker films and lower proton activity causing ‘decoupling’ of the protein redox chemistry due to a reduced electrical conductivity of the TiO₂ phytate film connecting hemoglobin with the electrode. This is the first example of a bi-layer nanofilm structure where the underlying TiO₂ phytate film controls the electrochemical properties of the hemoglobin modified top-layer.     

氧化锌纳米棒微结构光电极的制备

通过两步法,即首先热分解醋酸锌制备氧化锌晶种层,在晶种的诱导下,再采用低温水热法在氟掺杂的SnO₂导电玻璃(fluorine-doped tin oxide, FTO)基底导电面上成功制备出高取向性的氧化锌纳米棒阵列光电极。系统研究了前驱液浓度、溶液pH值、反应时间等实验条件对光电极微结构的影响。实验结果表明在一定变化范围内,随着前驱液浓度和溶液pH值的增大,纳米棒的直径增大;随着反应时间的延长,纳米棒的长度增长。将氧化锌纳米棒阵列薄膜制作成染料敏化太阳电池(dye-sensitized solar cell, DSSC)的光电极,并对电池的I-V特性进行了表征。     

Influence of the degree of ionization on the growth mechanism of poly(diallyldimethylammonium)/poly(acrylic acid) multilayers

pH‐dependent growth laws of the mass coverage Γ(n) of poly(diallyldimethylammonium) chloride and poly(acrylic acid) (PAA) layer‐by‐layer films are analyzed by Quartz Crystal Microbalance‐D. (Attenuated Total Reflection)‐FTIR spectroscopy shows a degree of dissociation of acrylic acid groups in the films identical to that in solution. Apart from pH‐regimes of differently pronounced exponential and linear growth, the corresponding kinetics indicate pH‐dependent adsorption, reorganization, and diffusion processes. As the thickest films form with almost uncharged PAA (low pH), the results can only partly be explained by the dissociation degree of PAA in the film. For intermediate and high pH values chain interdiffusion as a mechanism for nonlinear growth is strongly dependent on the charge density of the PAA chains. However, at low pH other types of interactions, most likely ion–dipole interactions, play a major role in the multilayer growth. Furthermore, a change in the symmetry of growth can be observed in the low to intermediate pH range. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 425–434     

Influence of Ionic Strength on Electrochemical Responses of Myoglobin Loaded in Polysaccharide Layer‐by‐Layer Assembly Films

Two polysaccharides hydroxyethyl cellulose ethoxylate (HECE) and hyaluronic acid (HA) were assembled into {HECE/HA}_n layer‐by‐layer films on electrodes. The films were then immersed in myoglobin (Mb) solutions to load Mb into the films. The Mb‐loaded films showed a nearly reversible cyclic voltammetric (CV) peak pair at ?0.34 V vs. SCE in pH 7.0 buffers. The effect of ionic strength in Mb loading solutions and CV testing solutions on the CV response of the films was investigated. The direct electrochemistry of Mb loaded in the films could also be used to electrocatalyze the reduction of oxygen and H₂O₂ in solution.     

Morphologies and enzymatic degradability of melt-crystallized poly(3-hydroxybutyric acid-Co-6-hydroxyhexanoic acid)

The films of poly[(R)-3-hydroxybutyric acid-co-10mol% 6-hydroxy-hexanoic acid] (P[(R)-3HB-co-6HH]) were prepared by melt-crystallized method at various crystallization temperatures. The morphologies and properties of melt-crystallized films were characterized by means of x-ray diffraction, differential scanning calorimetry, optical microscopy, and scanning electron microscopy. All of the melt-crystallized films showed the banded spherulite morphology. The enzymatic degradation of melt-crystallized films was carried out at 37 °C in an aqueous solution (pH 7.4) of PHB depolymerase from Alcaligenes faecalis. The rate of enzymatic erosion was strongly dependent on the crystallinity of films, and the highest rate was as large as 2.15 mg·h⁻¹·cm⁻². After enzymatic degradation, the banded morphology of P[(R)-3HB-co-6HH] spherulites was visible, suggesting that PHB depolymerase predominantly hydrolyzes polymer chains on the edges of crystalline lamellar stacks.     

Fabrication of Covalently Attached Multilayer Film Electrode Containing Iron Porphyrin and Its Electrocatalysis Toward Sulfite

Construction of a highly stable covalently attached multilayer film electrode containing iron porphyrin was achieved by UV irradiation of ionic self‐assembled multilayer films of diazo‐resins (DAR) and anionic Fe(III)tetrakis(p‐sulfonatophenyl)porphyrin (FeTSPP). The multilayer films had been characterized by UV, IR spectra and cyclic valtammetry. The electrocatalytic transformation of sulfite to SO₄^2? by the multilayer film electrode containing FeTSPP was investigated. In 0.1 M NH₄OH? NH₄Cl buffer solution (pH 8.74) and 0.1 M borate buffer solution (pH 9.18) the electrocatalytic oxidation of sulfite through the multilayer film electrode can be performed. However, in acetate buffer solution (pH 4.0) the electrocatalytic reduction of sulfite by the multilayer film electrode had also good activity. The modified electrode also exhibited a fast response and good stability.     

Influence of solution conditions on formation of amphiphilic hyperbranched polyanion/linear polycation multilayer films

Amphiphilic hyperbranched polyester (P2) consisting of a hydrophobic core, surrounded by aromatic carboxylic acids, is self-assembled into aggregates in aqueous solution at pH region of 3.8–4.7 and in THF–water mixed solution at THF/water volume ratio of 1/100–1/10. With P2 in both aqueous and THF–water mixed solution as polyanion and linear poly(diallydimethylammonium chloride) (PDAC) as polycation, self-assembled films were successfully formed by layer-by-layer dipping. The solution condition of P2, including the pH of aqueous solution and the THF/water volume ratio, affected not only the absorption behavior of P2 but also the surface morphology and hydrophilicity of the films with P2 as the outmost layer. At lower pH or higher THF/water volume ratio the aggregation of P2 in solution was enhanced, thus resulting in higher adsorption rate for P2, more rough and less hydrophilic surface for the films.     

Scanning force microscopy and effective medium theory study of free-standing polyaniline thin films

The technique of scanning force microscopy was used to study the nanometer-scale structure of NMP cast films of polyaniline. Noncontact mode images provide direct evidence that polyaniline prepared in this form is a granular conductor. The films were found to consist of micrograins whose size and density were determined by the pH of the acid solution used to protonate the films. At pH 7, the polyaniline films exhibited a mostly disordered structure, with small 2–10 nm particles visible. Protonation at pH 5 to pH 3 resulted in partial agglomeration of the primary particles into larger bundles, with sizes up to 75 nm. Treatment in solution pHs of 2 or less resulted in films consisting of close-packed bundles of dimension 20–30 nm. The conductivity of the films exhibited a sharp rise beginning with protonation at pH 2 or less. Effective medium theory (EMT), was used to model the macroscopic conductivity of these films based on the SPM measured microscopic film structure. Using the size and size distribution of polymer micrograins or bundles in a modified EMT, we are able to obtain predicted conductivities that are close to the measured values for these films. © 1995 John Wiley & Sons, Inc.     

Electrochemical Investigation of Myoglobin in Layer‐by‐Layer Films Assembled with Sulfonated‐β‐Cyclodextrin

In this work, myoglobin (Mb) and sulfonated‐β‐cyclodextrin (S‐CD) were assembled into {S‐CD/Mb}_n layer‐by‐layer films on solid substrates. In pH 7.0 buffers, the {S‐CD/Mb}_n films assembled on electrodes showed a pair of well‐defined and nearly reversible CV peaks at about ?0.35 V vs. SCE. The stable CV response of {S‐CD/Mb}_n films could be used to electrocatalyze reduction of oxygen and hydrogen peroxide in solution. For comparison, another modified β‐cyclodextrin, carboxyethyl‐β‐cyclodextrin (C‐CD), was also assembled with Mb into {C‐CD/Mb}_n multilayer films. The driving forces of the assembly were explored and discussed.     

pH-dependent behaviors of electroactive myoglobin loaded into layer-by-layer films assembled with alginate and hydroxyethyl cellulose ethoxylate

In the present work, strong polybase quaternized hydroxyethyl cellulose ethoxylate (HECE) and weak polyacid alginate (AA) were assembled into {HECE/AA} n layer-by-layer (LBL) films on electrodes by electrostatic interaction between them, and the films were then immersed in myoglobin (Mb) solution to load Mb into the films, designated as {HECE/AA}n-Mb. The {HECE/AA}n-Mb films showed a nearly reversible cyclic voltammetric (CV) peak pair at about -0.34 V vs SCE in pH 7.0 buffers for Mb heme Fe(III)/Fe(II) redox couple, and the surface concentration of electroactive Mb in the films (Gamma*) was affected significantly by the pH of Mb loading solution and testing solution. The amount of Mb loaded from pH 5.0 solution was much larger than that from pH 9.0 solution, which is mainly attributed to the higher degree of swelling, porosity, and permeability of {HECE/AA}n films at pH 5.0 than at pH 9.0. In addition, the electrostatic interaction between Mb and the AA component in the films might also play an important role in Mb loading. The pH of the testing solution where {HECE/AA}n-Mb films were tested by CV also influenced the Gamma* value, showing that the fraction of electroactive Mb among the total Mb loaded into the films increased remarkably as the pH of the testing solution decreased. This result is rationalized in terms of the pH-dependent film permeability toward counterions and the electron-hopping mechanism in electron transfer of redox proteins in the film phase. This model system may provide a general and effective approach to control the electroactivity of immobilized redox proteins in the multilayer assembly containing weak polyions by adjusting pH and may guide us to develop the new kind of controllable electrochemical biosensors based on the direct electrochemistry of enzymes.     

Electrochemical response of natural and induced passivation of high strength duplex stainless steels in alkaline media

The passivation of two high strength duplex stainless steels (HSSS) was investigated in alkaline solutions simulating the pore solution of concrete by the growth of natural and induced passive films. Induced passive films were generated both by cyclic voltammetry and by chronoamperometry. Natural passive films were spontaneously grown by the immersion of the steel in the alkaline electrolyte. These passive layers were characterised by electrochemical impedance spectroscopy, corrosion current density (i _corr) and corrosion potential (E _corr) monitoring. The effect of significant parameters, such as the pH in the HSSS/alkaline solution interface, the composition of the duplex stainless steels and the ageing of the passive layer, on the electrochemical performance of both induced and spontaneously grown passive films has been analysed. The increase of alkalinity highly influences the electrochemical performance of the passive film by promoting the formation of a passive layer with a less resistant electrochemical response. The electrochemical behaviour of the passive layer is also affected by the alloying elements like Mo or Ni. Both natural and induced passive films show similar electrochemical trend with respect to significant parameters such as the pH and the composition of the steel. The ageing of the spontaneously grown passive layer promotes a higher resistive electrochemical response which might be related to the enrichment of the passive layer in non-conducting (or semi-conducting) oxides.     

Effect of dipping solution pH values on electrostatic layer-by-layer self-assembly of side-chain azo polyelectrolyte

The effect of pH value on the electrostatic layer-by-layer self-assembly and the photo-responsive behavior of Poly{2-[4-(4-ethoxyphenylazo)phenoxy]ethyl acrylate-co-acrylic acid} (PEAPE) was studied. Results show that in the studied pH value range, the lower the pH value is, the higher is the UV-vis absorbance and the larger is the thickness of the multilayer films. FTIR studies indicate that the azo polyelectrolyte exhibits a different ionization degree in solutions with different pH values. The higher absorbance and the larger thickness of the layer-by-layer films can be attributed to the low ionization degree and the shrinkage conformation of PEAPE in the solution with low pH values. FTIR analysis also confirms that the driving force for layer-by-layer self-assembly of PEAPE and PDAC is the electrostatic interaction. __________ Translated from Acta Polymerica Sinica, 2007, 5: 440–445 [译自: 高 分子学报]     

External Stimuli Responsive Characteristics of Epoxy‐Polyamide/Starch Blend Films

Abstract

Polymeric films of varying crosslink densities and of different molar‐concentrations were prepared from the epoxidized oil/diglycedyl ether of bis‐phenol A (DGEBA) epoxy/polyamide/starch by blending at ambient temperature. The influences of external stimuli such as pH, temperature, ionic strength of the swelling media, and the type of buffer on the equilibrium swelling properties were investigated. Polymeric films showed a typical pH and temperature response such as low‐pH and low‐temperature have maximum swelling while a high‐pH and high‐temperature show almost complete deswelling. A change in the ionic strength of the swelling solution from 0.01 to 0.2 M caused a decrease in the equilibrium degree of swelling of polymeric films. Oscillatory swelling was also observed and investigated in response to changes in the pH of the solution. The morphology of selected polymeric films were explained by scanning electron microscopy (SEM) and correlated with mechanical strength.     

Characterization and Electrocatalytic Properties of Composite Poly(new fuchsin) and Phosphomolybdate Films

Organic/inorganic hybrid films of poly(new fuchsin) and phosphomolybdate (PMo₁₂O ) have been prepared in acidic aqueous solutions. These new combination films are stable, electrochemically active, and can be produced on glassy carbon, platinum, gold, and transparent semiconductor tin oxide electrodes. An electrochemical quartz crystal microbalance along with cyclic voltammetry and UV‐visible absorption spectroscopy were used to study the in situ growth of the hybrid films. The hybrid poly(new fuchsin) and PMo₁₂O films showed four obvious redox couples, and when transferred to various acidic aqueous solutions, the formal potentials of the four redox couples were found to be pH dependent. The electrocatalytic reduction of ClO , BrO , IO , SO , S₂O , H₂O₂, and NO by the hybrid poly(new fuchsin) and PMo₁₂O films was achieved in acidic aqueous solutions. In an aqueous solution at pH 1.5, a hybrid poly(new fuchsin) and PMo₁₂O film showed a higher electrocatalytic reduction activity of IO than BrO or ClO , and the order of electrocatalytic activity was IO >BrO >ClO . The order of electrocatalytic reduction of SO , S₂O , H₂O₂, and NO by hybrid poly(new fuchsin) and PMo₁₂O films in an aqueous solution at pH 1.5 was NO >H₂O₂>S₂O and SO . The electrocatalytic reactions of the poly(new fuchsin) and PMo₁₂O films were investigated using the rotating ring‐disk electrode method.