Stable Polymer Films Research Articles

Anionic Polymer-Modified Electrodes Based on a Macrocyclic Nickel(II) Complex for Selective Determination of Dopamine in the Presence of Ascorbic Acid

occurs with relatively higher concentrations of ascorbic acid (AA). When DA is oxidized to DA quinone, AA is oxidized at a similar potential to DA at ordinary solid electrodes, which decreases the electrodes' selectivity for DA. To increase the selectivity for DA, electrodes can be modified with materials that can separate DA and AA electrochemically. Most of these materials are cationic or anionic polymers, 3-6 because cationic DA and anionic AA at the physiological pH of 7.4 can be separated by the exclusion effect of polymer films of the same charge. In addition to ionic polymers, self-assembled monolayers 7 and carbon nanotubes 8 also increase the selectivity for DA. Anionic polymer-modified electrodes are useful for increasing the selectivity toward cationic DA over anionic AA. The desirable anionic polymer material should be well suited to biological samples. The macrocyclic Ni(II) complex is readily electropolymerized by oxidation or cycling the potential, and the stable polymer film has a catalytic effect on substances such as AA. 9 To obtain an anionic polymermodified electrode, the macrocyclic Ni(II) complex can be used with an anionic polymer or a macrocyclic Ni(II) complex with an introduced carboxylic acid group. The anionic macrocyclic Ni(II) complex also readily forms a negatively charged electropolymerized film on an electrode surface. Polyurethane (PU) containing γ-benzyl L-glutamate segments (PUBLG) is a new polymer, 10 which is a segmented PU. Segmented PUs are used in devices that contact blood, such as catheters and artificial hearts, because of their good mechanical properties and tolerance of blood. 11,12 A hydrophobic PUBLG film can be converted into an anionic hydrophilic PU film on introducing carboxylate groups by hydrolysis. We applied an anionic PU film to the selective determination of DA for the first time. This study examined the selectivity of anionic polymermodified electrodes for DA over AA and their suitability for use with human urine. Their sensitivity and reproducibility were evaluated using amperometry with flow injection. These anionic polymers were compared with Nafion, a perfluorosulfonated ion-exchange material.

Electrochemical synthesis of polyaniline on mild steel in acetonitrile–LiClO4 and corrosion performance

Polyaniline film could not be obtained on mild steel by direct electrooxidation of aniline in LiClO4 containing acetonitrile medium (ACN–LiClO4), because sufficient passivity of the surface could not be provided. This non-passivated metal undergoes intense dissolution, in potential region at which the monomer oxidation happens and this event prevents the formation of stable polymer film on the surface. Therefore, the electrode surface was coated with very thin polyaniline (PANi), polypyrrole (PPy) primer coatings, in monomer containing aqueous oxalic acid solution, and then the synthesis of top PANi film was achieved in aniline containing ACN–LiClO4 successfully. The corrosion behavior of PANi/PANi and PPy/PANi coated MS samples were investigated in 3.5% NaCl solution, properly. For this aim, anodic polarization curves and open circuit potential–time (Eocp–t) variation and electrochemical impedance spectroscopy (EIS) techniques were used. It was shown that PPy/PANi coating could provide much better protection for longer periods than PANi/PANi coating against the corrosion of MS. This behavior was explained with better barrier property of PPy/PANi. After 240h of immersion time in corrosive test solution, the protection efficiency value was 97.0%, for PPy/PANi coated electrode.

Low-density polymer thin film formation in supercritical carbon dioxide

We report a method for producing stable low-density polymer films by using supercritical carbon dioxide (scCO2). Two different molecular weight polystyrene films with various thicknesses were exposed to scCO2 along the density fluctuation ridge in P–T phase diagram. The swollen structures could be then frozen by flash evaporation of CO2 without forming additional voids. X-ray reflectivity data clearly showed that exposure to scCO2 could be used to produce uniform low-density films of about 2Rg thick or less, where Rg is radius of polymer gyration.

Novel diazosulfonate terpolymers for the preparation of structured functionalized surfaces: Synthesis and characterization

We report the synthesis and characterization of novel diazosulfonate copolymers and terpolymers by free-radical polymerization for the preparation of ultrathin films. Such films were covalently linked to silicon and glass substrates after a spin-coating and annealing process using 3-(trimethoxysilyl)propyl methacrylate as the adhesive comonomer. The polymers were characterized by NMR and IR spectroscopy and ellipsometry, and contact-angle measurements were used to analyze the film properties. The light-sensitive but thermally stable polymer films can be structured successfully by UV light down to the micrometer scale. The patterns written into the diazosulfonate film were produced by a UV laser without a mask. The photolysis in solution and in film was examined by UV spectroscopy. UV imaging: area selective representation of the UV transmission between 430 and 450 nm over a 60 × 60 μm2 area of a spin coated film of copolymer 2. Pre-structuring with a He-Cd laser (at 325 nm) resulted in a ring-shaped structure of 30-μm diameter showing a higher transmissivity (brighter area) resulting from the reduced absorption of the polymer film (decomposition of the diazosulfonate functions).

Control of Dewetting Dynamics by Adding Nanoparticle Fillers

Producing a stable polymer film is a challenge, because dewetting tends to rupture the film. To overcome this drawback, it is essential to control the factors responsible for stabilizing polymer films during processing. Here, we report on a unique strategy to control the rate of dewetting by dispersion of small amount of carbon black and colloidal Si nanoparticle fillers in the polymer thin film. Optical microscopy, AFM and TEM have been used to study the surface and interfacial structure in the vicinity of growing holes. The rate of dewetting is drastically different when filler particles are added to the polymer and strongly depends on nanoparticle concentration in the film. Even though the particle sizes are similar, their effects on the dynamics are very different. We explain our findings in the form of interaction between the polymer chains and particle surface.

Electrodeposition of ring-substituted polyanilines on Fe surfaces from aqueous oxalic acid solutions and corrosion protection of Fe

The electrochemical polymerization of several ring-substituted anilines namely of o-toluidine ( o-Tol), m-toluidine ( m-Tol), o-anisidine ( o-Anis) and o-chloroaniline ( o-ClAn) was carried out on passivated Fe surfaces. Thin polymeric films were deposited by cyclic voltammetry, potentiostatic or galvanostatic techniques on the Fe-disc electrode from aqueous oxalic acid solutions. Well-defined cyclic voltammograms showing the electroactivity and growth of polymers were observed during each potential cycle. The electrochemical response and the surface morphology of the deposited polymeric films of substituted polyanilines were characterized in comparison with the non-substituted polyaniline films on Fe. Adherent and relatively stable polymeric films were obtained for o-Tol, m-Tol and o-Anis. These films show protective properties against corrosion of Fe in sulfuric acid solutions stabilizing the Fe passive state. Their anti-corrosion behavior, although slightly poorer than that of the non-substituted polyaniline, bears strong similarities with that of the polyaniline. A less conductive polymer with a very poor stability and protective ability against the corrosion of Fe was obtained for o-ClAn.

Strategy for controlling the Kolbe Electrosynthesis in the presence of aromatic fragments and amino groups in the molecule

A general characteristic of processes that occur during anodic oxidation of phenylacetic and phenylpropionic acids and derivatives of α- and β-amino acids on platinum electrodes in methanol and mixed pyridine–methanol solutions is given. From preparative electrolyses in stagnant and flow-through reactors, conditions are determined under which the dimerization (Kolbe electrosynthesis) is least complicated by the formation of polymer products. Properties of removed electrodes, on which stable polymer films formed during the electrosynthesis, are examined. For films formed in certain conditions on the cathode, the presence of a quasi-reversible redox transition is demonstrated. Such films contain disperse platinum codeposited with polymer as a result of the anode dissolution in the cells with common compartments. In principle, the film-modified electrodes can be used for controlling anodic decarboxylation.

Electrosynthesis of conducting polymer films from the azo dye methoxy red

Anodic polymerization of the azo dye methoxy red (4-methoxybenzene azo-1,3-diaminobenzene) on platinum electrodes in 1 M HCl in 50% v/v ethanol/water was found to yield thin and stable polymeric films. The films were electroactive in acidic solutions and the activity diminished as the acidity decreased. The pair of symmetrical redox peaks at a formal redox potential, (E∘)pH=0 = 0.61 V vs SCE, with a Nernstian slope dE/dpH = 0.06 V, is attributed to a 1:1 proton + electron elimination (on oxidation)/addition (on reduction) at the amino/imino linkages which connect the aromatic nuclei. Chronocoulometric plots indicated that the transport of the solvated protons, and probably Cl− ions, through the film is the rate-determining step of the above redox processes. The rate of electron transfer reactions of the redox couple [Fe(CN)6]3−/4− on poly-methoxy red-covered platinum electrodes decreased by a factor of more than two orders of magnitude, compared to the bare electrodes.

Alkane-tetrathiol induced formation of remarkably stable self-assembled monolayer and polymer films containing electroactive tetrathiafulvalene moieties on metal electrodes

Remarkably stable self-assembled monolayer and polymer films composed of a new tetrathiafulvalenyl-tetrathiol have been formed on metal electrodes: this is a new class of surface modification by self-assembly and electrochemical polymerization using the same alkane-tetrathiol.

Synthesis of NLO diacrylate monomers and their photocopolymerizations with LC diacrylate monomers in mixed liquid crystalline state

The photocopolymerization (photocrosslinking) of mixed liquid crystals (LCs) consisting of LC diacrylate monomers and nonlinear optical (NLO) diacrylate monomers exhibiting no liquid crystallinity under contact poling at optimum temperature was investigated to obtain a thermally stable NLO polymeric material. Novel NLO monomers, BAASA and BAOSA, as well as LC monomers, BAOOB3 and PAOB, were synthesized and the liquid crystallinity of their mixed LCs was investigated. The affinity of BAOSA with the LC monomers is generally better than that of BAASA. LC mixtures prepared using BAOOB3 as LC matrix show only a smectic phase and do not respond to poling though fixation of the mixture by photocrosslinking occurs tightly. A PAOB matrix results in a nematic phase but not a smectic phase and the LC mixture responds not only to poling but also to photocopolymerization in the nematic phase. The photocrosslinking reaction of a BAOSA/PAOB (mole ratio 1/9) mixture under poling at 129°C (nematic phase) proceeds effectively and gives a thermally stable polymer film with a χ33(2) value of 1.2–1.7 × 10−8 esu1 esu = electrostatic unit; 1 esu = 2.693 × 1014 C3/J2. , while the polymer film formed by photocrosslinking at 140°C (isotropic phase) shows a one order lower χ33(2) value (3–5 × 10−9 esu).

Synthesis of NLO diacrylate monomers and their photocopolymerizations with LC diacrylate monomers in mixed liquid crystalline state

The photocopolymerization (photocrosslinking) of mixed liquid crystals (LCs) consisting of LC diacrylate monomers and nonlinear optical (NLO) diacrylate monomers exhibiting no liquid crystallinity under contact poling at optimum temperature was investigated to obtain a thermally stable NLO polymeric material. Novel NLO monomers, BAASA and BAOSA, as well as LC monomers, BAOOB3 and PAOB, were synthesized and the liquid crystallinity of their mixed LCs was investigated. The affinity of BAOSA with the LC monomers is generally better than that of BAASA. LC mixtures prepared using BAOOB3 as LC matrix show only a smectic phase and do not respond to poling though fixation of the mixture by photocrosslinking occurs tightly. A PAOB matrix results in a nematic phase but not a smectic phase and the LC mixture responds not only to poling but also to photocopolymerization in the nematic phase. The photocrosslinking reaction of a BAOSA/PAOB (mole ratio 1/9) mixture under poling at 129°C (nematic phase) proceeds effectively and gives a thermally stable polymer film with a X 33 (2) value of 1.2-1.7 x 10 -8 esu a , while the polymer film formed by photocrosslinking at 140°C (isotropic phase) shows a one order lower X 33 (2) value (3-5 x 10 -9 esu).

Electrochemical syntheses and doping properties of poly(3,3′-dialkylsulfanyl-2,2′-bithiophene)s: novel materials which exhibit facile n- and p-dopability

Novel and stable electroactive polymer films which can undergo facile electrochemical p- and n-doping are successfully prepared for the first time from the electrochemical polymerization of symmetrical 3,3′-dialkylsulfanyl-2,2′-bithiophenes with long pendant chains.

Electropolymerization of 2-hydroxy-3-aminophenazine (HAPh): properties of pHAPh films and kinetics of oxidation and incorporation of dihydroxybenzenes at Pt/pHAPh electrodes

2-Hydroxy-3-aminophenazine (HAPh) gives stable redox active polymer (pHAPh) films after oxidative electropolymerization on Pt, Au, glassy carbon and ITO electrodes. pHAPh is a new ladder polymer with structures and redox properties closely related to those of poly( o-phenylenediamine) and poly( o-aminophenol). The electropolymerization of HAPh on Au is accompanied by electrodissolution of the Au substrate. Dissolved Au species are redeposited producing dispersed gold crystallites in the organic polymer film. The pHAPh film can respond to dissolved organic species, such as dihydroxybenzenes and p-benzoquinone, in the electroinactive potential range. For the oxidation of dihydroxybenzenes the rate controlling processes are all three contributory steps, i.e. charge transport and diffusion of substrate within the film and cross-exchange electron transfer reaction between the substrate and the redox sites of the film. For p-benzoquinone, the reduction process is solely governed by substrate diffusion within the film. RRDE measurements have shown that the dihydroxybenzenes are incorporated in the pHAPh film in the reduced state. There is also evidence that p-benzoquinone is also incorporated in the film when it is in the oxidized state.

Electron transfer mediation characteristics of conducting Polymer Films of 4(5-chloro-2-pyridyl)-1,3-diaminobenzene cobalt complex

Stable electroactive polymer films of cobalt complex of 4(5-chloro-2-pyridylazo)-1,3-diaminobenzene (abbreviated as PCoL2) were prepared on glassy carbon electrodes by the oxidative polymerization of the complex in acetonitrile. Two pairs of reversible redox peaks for PCoL2 films were observed. The first pair is attributed to the electroactivity of the skeleton of the polymer and the other is attributed to the redox processes of the CO3+/2+ couple. The surface concentration of the electroactive Co sites was found to increase with increasing the film thickness. Mediation of reduction of [Fe(CN)6]3− by PCoL2 films was investigated by steady state measurements. The rate of the mediated reaction was found to be controlled by the rate of the charge propagation within the film & the rate of diffusion of the substrate through the film beside the rate of diffusion of the substrate to the electrode. Thin films were found to be potentially more efficient for the mediation than thicker films.

Redox behaviour of Cu2+/Cl? system at poly-4-(2-pyridylazo)resorcinol modified Glassy Carbon Electrodes

Thin, adherent and stable polymeric films of 4-(2-pyridylazo)resorcinol (abbreviated as PPAR) were prepared by oxidative polymerization in 0.2 M NaOH solutions. PPAR films deposited on GC electrodes were found to inhibit the electron transfer reactions of the couple [Fe(CN)6]3−/4−. The redox behaviour of CuCl2 in 0.5 M KCl at bare and PPAR-covered GC electrodes was studied by cyclic voltammetry, RDE voltammetry and chronoamperometry. At PPAR-covered electrodes the peak potential of deposition of Cu occurs at ≃ 260 mV more cathodic potential than bare electrodes whereas the redox peaks of Cu2+/1+ and the oxidation of Cu → Cu1+ occur at the same potentials. Catalysis of thc redox processes of the couple Cu2+/1+ at PPAR-covered electrodes is attributed to incorporation of the redox species by chelation and electrostatic attraction. The diffusion coefficient of Cu2+ species (D = 0.29 × 10−5cm2 S−1) at PPAR-covered electrodes was found to be less than at bare electrodes (D = 0.95 × 10−5 cm2 S−1) whereas the effective bulk concentration (C = 28 mM) is higher than the used concentration: 10 mM.

The influence of the electron-electron Coulomb interaction on the low-temperature conductivity of ion-irradiated polyimide films

Abstract The transport mechanism of charge carriers in thermally stable polymer (polyimide) films, irradiated with a combination of Ar+ and Ga+ ions, has been investigated. Such irradiation increased the electrical conductivity of modified layers by more than seven orders of magnitude, so that it reached 103 S cm−1. It is concluded that the electron-ectron Coulomb interaction influences the low-temperature conductivity of ion-irradiated polyimide films near the metal-insulator transition, just as it does in the case of crystalline and amorphous semiconductors. Values of the localization radius, the permittivity and the density of the localized states are determined.

Reactions of organonitrogen molecules with nickel(100)

The adsorption and reaction of a variety of organonitrogen compounds on a Ni(100) surface have been examined with temperature-programmed reaction. Auger electron spectroscopy, and infrared spectroscopy. Monomethylamine adsorbs via the nitrogen lone pair of electrons and then undergoes C-N bond scission yielding adsorbed carbon, dihydrogen, and ammonia. Aniline ..pi..-bonds to the surface and polymerizes to form a thermally stable poly(aniline) surface film. Pyridine undergoes a temperature-induced orientational transformation. At low temperatures pyridine adsorbs with its ring parallel to the surface. At higher temperatures it appears to form an ..cap alpha..-pyridyl species with an activation barrier of 85 kJ/mol. Methyl groups on 2,6-lutidine sterically hinder this reaction. Methyl groups on 3,5-lutidine stabilize bonding via the nitrogen lone pair of electrons. The methyl groups on 3,5-lutidine increase electrophilic addition activity relative to pyridine and lead to polymerization of 3,5-lutidine, forming a thermally stable polymer film. Pyrimidine reacted in almost identical fashion to pyridine, suggesting that increased nucleophilic activity had little effect on the reaction behavior of heterocyclic compounds and that electrophilic reactions predominate.

Electrochemical preparation of a polyparaphenylene film and a polyparaphenylene/polyacrylamine functional film

We have first found the way to obtain a uniform and flexible polyparaphenylene (PPP) film by electrochemical polymerization of benzene in concentrated sulphuric acid with an anhydrous Lewis acid as catalyst. It is evident that concentrated sulphuric acid plays an important role in the electrochemical polymerization of benzene. It protonates benzene into benzenium. The rotation of the working electrode is an important condition for obtaining uniform and flexible PPP films. The thickness of the PPP film can be controlled by the electricity used for polymerization and the amounts and kinds of catalysts employed. The colour of the PPP film changes from transparent yellow to black, depending on the thickness. The PPP film is electroactive in concentrated sulphuric acid. The stable polymer film (PPP) is a suitable underlayer for polyacrylamine (PAA) formation by the electrochemical polymerization method. This PPP/PAA film has high potential for applications in the extraction of trace metal ions, ion exchange and in catalysis.

The Polymerization of Diacetylenes on Solid Surfaces

AbstractThe influence of solid surfaces on the polymerization of diacetylenes has been studied using 3,5‐octadiyn‐1,8‐diol as a model compound. The first molecular layers on polar surfaces are adsorbed by hydrogen bonds. Their relative orientation hinders the polymerization of these molecules. Subsequent layers can be polymerized by UV radiation. After the unreacted monomer has been extracted a highly stable polymer film remains on the surface.

Polymerization induced by electron‐beam irradiation of octadecyl methacrylate in the form of a multilayer or monolayer

AbstractIn continuation of the previous series of studies, polymerization of octadecyl methacrylate (ODMA) induced by electron beams has been investigated in a form of its multilayer or monolayer in an attempt to prepare a stable thin polymer film having a regular layer structure. ODMA multilayers were prepared by the Langmuir‐Blodgett technique and irradiated with electron beams from a Van de Graaff accelerator. Multiple reflection infrared spectroscopy and x‐ray diffractometry revealed that the ODMA multilayer was polymerized to give a thin polymer film having a regular layered structure when irradiated in nitrogen atmosphere, but no indication of polymerization was observed when irradiated in air. A preliminary study on the ODMA monolayer at a nitrogen–water interface indicated that the monolayer was polymerized.