Electrochemical synthesis and redox behaviour of polypyrrole coatings on copper in salicylate aqueous solution

In this work, polypyrrole (PPy) coatings have been successfully electrodeposited on copper substrates from aqueous salicylate solutions. Homogenous and uniform films can be grown under galvanostatic or potentiostatic control without noticeable substrate dissolution. The redox behaviour obtained for the films is similar to that displayed by PPy grown under the same conditions on noble metals. Strong adherence to copper is observed as far as PPy is in its oxidised state but it is lost when the system is subjected to potentials lower than −0.5 V versus saturated calomel electrode (SCE).     

In situ observation of dynamic elastic modulus in polypyrrole actuators

Polypyrrole is a leading conducting polymer actuator, but the factors that influence its performance when actuated under load in devices (such as the polymer stiffness) are not yet fully understood. To this end, we have probed the dynamic elastic modulus of polypyrrole in situ during actuation in a variety of electrolytes. As part of this study, we demonstrate that the electroactive response in dilute 1-butyl-3-methylimidazolium hexafluorophosphate can be changed from cation- to anion-dominated by adjusting the applied potential waveform. We observe that when conservative electrochemical conditions are applied in order to avoid dual ion movement or significant transfer of neutral solvent, the stiffness is determined by level of counterion swelling. The elastic modulus decreases during the net influx of ions into the bulk polymer and increases as these ions are expelled, regardless of whether the electroactive response is cation- or anion-dominated or whether there is a neutral solvent present in the electrolyte. This effect is quite significant, and we have observed up to a 3× increase in elastic modulus upon actuation in neat 1-butyl-3-methylimidazolium hexafluorophosphate.     

Electrochemistry of conductive polymers XXXV: Electrical and morphological characteristics of polypyrrole films prepared in aqueous media studied by current sensing atomic force microscopy

Electrical and morphological characteristics of polypyrrole (PPy) films electro-deposited in four different aqueous electrolyte solutions including p-toluenesulfonate, dodecylsulfate, poly(styrenesulfonate), and perchlorate have been investigated using current-sensing atomic force microscopy. Experimental parameters including the electrolyte, applied current density, and deposition time were shown to affect the morphologies and current images of PPy films thus prepared. The PPy films were galvanostatically prepared under the identical conditions except for different electrolytes; the globular-shaped topographic structures with the unusually large sizes were obtained in dodecylsulfate. The p-toluenesulfonate doped PPy film showed the highest average conductivity whereas the perchlorate doped one showed the lowest of all the films prepared.     

The electrochemical behaviour of copper in sodium salicylate aqueous solutions

Cyclic voltammetry has been used to investigate the behaviour of copper surfaces in sodium salicylate aqueous solutions. The observed copper anodic passivation dependence on the presence of salicylate ion in solution is explained. The analysis of the experimental data supports the formation of a complex passivating film formed by a Cu₂O inner layer and a mixed cupric oxide/cupric salicylate outer layer; this film provides a partial passivation of the copper surface and can be completely removed upon excursion to negative potentials values; the composition of the passivating layer depends on the electrolyte nature, i.e. sodium salicylate ion and solution pH, and on the potential programme the copper electrode is subjected to.     

Study of polaron and bipolaron states in polypyrrole by in situ Raman spectroelectrochemistry

The transitions from the reduced-polaron-bipolaron states of polypyrrole (ppy) were analyzed by in situ Raman spectroelectrochemistry. The distinct vibrational modes presented by the polymer in different oxidation levels were assigned to specific signatures of polaron and bipolaron states. As the polymer was oxidized from the neutral state, an intermediary phase featuring vibrational bands from both the benzoid (reduced) and the quinoid (oxidized) forms were observed. This intermediary phase was correlated to the polaron state. The results were compared with previous ESR data that confirm the presence of polaron and bipolaron states in the potential region where the vibrational modes of these phases were identified.     

Electrodeposition of homogeneous and adherent polypyrrole on copper for corrosion protection

Electrochemical synthesis of polypyrrole (PPy) on copper electrodes is researched using different techniques. The synthesised films are found to be very adherent and homogeneous. The corrosion behaviour of Cu/PPy is assessed in a 3.5% NaCl solution using polarisation curves and open circuit potential-time. The relationship between porosity and anticorrosive properties is demonstrated. The chronopotentiometry technique is seen to be the best to produce a good coating that yields good protection against copper corrosion for long immersion times.     

Correlation between ion-exchange properties and swelling/shrinking processes in hexasulfonated calix[6]arene doped polypyrrole films: ac-electrogravimetry and electrochemical atomic force microscopy investigations

Electrogenerated polypyrrole films doped with hexasulfonated calix[6]arenes were subjected to ac-electrogravimetry and electrochemical atomic force microscopy (EC-AFM) studies in aqueous potassium nitrate solutions. The former technique reveals that these films are mainly cation exchangers although solvent molecules (H₂O) and anions (NO₃⁻) are also exchanged, in much lower amounts, in the course of the doping/undoping process. Unexpectedly, within the potential range encompassing this process, K⁺ cations were found to be exchanged for more cathodic potentials whereas H₃O⁺ are exchanged for more anodic potentials. EC-AFM investigations revealed substantial shrinking and swelling during the oxidation (doping) and reduction (undoping) processes respectively. An obvious correlation can easily be built between these observations: the oxidation of the polymer films provokes an expulsion of the cations, as expected from cation exchanger polymer films, and therefore a decrease of the volume (and thickness) of these films whereas their reduction causes an insertion of cations and an increase of their volume (and thickness). This electromechanical mechanism is amplified by the simultaneous exchange of free water molecules. Suggestions based on these observations, on structural characteristics of polypyrrole films, and on complexation ability of hexasulfonated calix[6]arenes incorporated in the films are discussed to explain (i) the change of the identity of the exchanged cations as a function of the potential, (ii) the exchange of free water molecules and, (iii) the exchange of small amounts of nitrate ions.     

Application of atomic force microscopy and scaling analysis of images to predict the effect of current density, temperature and leveling agent on the morphology of electrolytically produced copper

Atomic force microscopy (AFM) was used to study the morphology of electrodeposited Cu at current densities from 183 to 253 A m⁻². Digital image analysis was employed to parameterize the morphological information encoded in AFM images and to extract information concerning the mechanism of the electrodeposition reaction. It has been shown how the limiting roughness, δ, the critical scaling length, L_c and the aspect ratio, 4δ/L_c, vary as a function of the deposition time and electrodeposition conditions, such as temperature, current density and the amount of organic additives. It has been demonstrated how laboratory experiments of short duration and the scaling analysis of AFM images can be used to predict roughness of the metal sample after 2 weeks of industrial electrorefining.     

Electrochemical reduction modeling of copper oxides obtained during in situ and ex situ conditions in the presence of acetic acid

We used the potentiodynamic reduction technique to study the mechanism of copper oxide formation in the presence of acetic acid. We performed all reductions under neutral conditions (0.1 M KCl) until hydrogen evolution. We produced the copper oxides in an environment containing 0, 500, and 800 ppb acetic acid at high relative humidity. We then compared experimental results between electrochemically produced oxide films obtained by imposing anodic potentials to copper specimens in several concentrations of pure acetic acid (1, 0.1, 0.01 and 0.001 M). We found that, as the concentration of the acid decreases, the formation of the copper oxide (I) increases. We also found the same peaks in samples produced under the synthetic environment. We modeled the curves, taking into account the electrochemical reduction of copper (II) oxide (CuO), amorphous cuprite (Cu₂O)_am, intermediate cuprite (Cu₂O)_in, crystalline cuprite (Cu₂O)_cr, and hydrogen. These oxides have been previously detected in similar conditions. We found no evidence of copper carboxylate founding samples produced by the electrochemical method.     

In situ AFM investigation of crazing in polybutene spherulites under tensile drawing

This report deals with the study of the plastic deformation processes of semi-crystalline polymers at the micrometric and nanometric scales by atomic force microscopy. Capturing images from the same locus of the sample as a function of strain allows in situ observation of the processes. New experimental findings regarding initiation, growth and coalescence of crazes in poly(1-butene) are reported. The benefits of the technique are emphasized in comparison with previous studies carried out by transmission electron microscopy on ultra-thin films of various semi-crystalline polymers. The present situation is claimed to be closely representative of bulk deformation owing to the much greater sample thickness in comparison with the characteristic craze size. The occurrence of crazes oblique to the principal tensile stress is discussed in terms of triaxiality of the local stress field within the spherulites.     

Influence of pH on the synthesis and properties of polypyrrole on copper from phytic acid solution for corrosion protection

Polypyrrole (PPy) films were deposited on copper from “green” inhibitor of phytic acid solution for corrosion protection of copper. The corrosion protection property of the PPy layer was studied by an immersion test in a NaCl aqueous solution. The polymerization process of PPy on copper changed with the pH values of phytic acid solution and current density applied. When one oxidized bare copper in phytic acid solution at various pHs containing pyrrole monomer, a thin layer consisting of complex compound of Cu-phytate was firstly formed, followed by the formation of the PPy layer doped with phytate anion on the complex compound layer. The complex compound layer passivated the copper surface and its thickness increased with the lower pH value of the solution and the lower current density applied. It was found that the PPy coating prepared in the phytic acid solution at pH 4 exhibit the most protective property against copper corrosion.     

Morphology,nanomechanical and thermodynamic surface characteristics of nylon 6/feather keratin blend films: an atomic force microscopy investigation

The surface structure and nanomechanical properties of solution‐cast nylon 6 (NY6)/feather keratin (FK) blend films were investigated using a combination of tapping‐mode atomic force microscopy (AFM) phase imaging and nanoscale indentation. A tendency for a nanoscale phase separation between NY6 and FK in their various blends was judged based on the blend phase images. The surface topography and roughness analysis of the AFM height images revealed that FK‐rich blends had coarser surfaces than NY6‐rich ones, possibly due to the heterogeneous nature of the FK chemical structure. Amplitude–phase–distance measurements involving the assignment of the darker and brighter regions of the phase images to NY6‐rich and FK‐rich, respectively, or vice versa led to the recognition of a phase inversion in the blend containing 40 wt% FK. The occurrence of the phase inversion phenomenon was related to the significant difference between the molecular weights of the blend constituents. Analysis of nanoindentation data showed that blending FK and NY6 at various ratios resulted in mixtures with modified mechanical and adhesion features. On the one hand, the NY6 component was responsible for an enhanced elastic modulus and stiffness of the blends, and on the other hand, the FK component provided higher pull‐off force and work of adhesion for the samples. A new approach is also proposed to directly determine the surface energy (γ) values of samples from the nanoindentation data. The excellent consistency between the calculated γ values and the results obtained from contact angle measurements lends credence to the proposed approach. Copyright © 2012 Society of Chemical Industry     

Sweet aqueous solution for electrochemical synthesis of polypyrrole part 1B: On copper and its alloys

The electrochemical synthesis of polypyrrole (PPy) on copper and brass has been successfully achieved in sodium saccharinate and pyrrole aqueous medium. The synthesized coating under several electrochemical techniques such as cyclic voltammetry, galvanostatic and potentiostatic is homogeneous and adherent. PPy has been characterized by SEM, XPS, IR and Raman spectroscopy and its quality has been confirmed. The doping level obtained from N 1s XPS signal of the oxidized PPy depends on the electrochemical technique used to produce the film. The corrosion performance of PPy/copper and PPy/brass has been evaluated in 3% NaCl and 0.1 M HCl using linear polarization and electrochemical impedance spectroscopy. The results show that PPy coating electrodeposited from sodium saccharinate exhibits significant corrosion protection properties.     

Surface morphology and nodule formation mechanism of cellulose acetate membranes by atomic force microscopy

By the use of atomic force microscopy (AFM), formation mechanism of nodular structure in cellulose acetate membranes was systematically investigated. Elementary factors affecting the nodule formation were delineated on the basis of both kinetic and thermodynamic considerations. It was shown that (1) the exact nature of nodular structure is thermodynamic equilibrium glassy state; nodular structure will vanish in the rubbery state; (2) the thermodynamic factor affecting nodule formation is the membrane formation temperature; with the membrane formation temperature decreasing, more chain segments are able to form nodular structures; (3) nodule formation is dependent on the segment rearrangement; variation of the solvent environment is the major kinetic factor affecting the segment rearrangement and nodule formation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1328–1335, 2003     

Reactivity at the film/solution interface of ex situ prepared bismuth film electrodes: A scanning electrochemical microscopy (SECM) and atomic force microscopy (AFM) investigation

Bismuth film electrodes (BiFEs) prepared ex situ with and without complexing bromide ions in the modification solution were investigated using scanning electrochemical microscopy (SECM) and atomic force microscopy (AFM). A feedback mode of the SECM was employed to examine the conductivity and reactivity of a series of thin bismuth films deposited onto disk glassy carbon substrate electrodes (GCEs) of 3 mm in diameter. A platinum micro-electrode (? = 25 μm) was used as the SECM tip, and current against tip/substrate distance was recorded in solutions containing either Ru(NH₃)₆³⁺ or Fe(CN)₆⁴⁻ species as redox mediators. With both redox mediators positive feedback approach curves were recorded, which indicated that the bismuth film deposition protocol associated with the addition of bromide ions in the modification solution did not compromise the conductivity of the bismuth film in comparison with that prepared without bromide. However, at the former Bi film a slight kinetic hindering was observed in recycling Ru(NH₃)₆³⁺, suggesting a different surface potential. On the other hand, the approach curves recorded by using Fe(CN)₆⁴⁻ showed that both types of the aforementioned bismuth films exhibited local reactivity with the oxidised form of the redox mediator, and that bismuth film obtained with bromide ions exhibited slightly lower reactivity. The use of SECM in the scanning operation mode allowed us to ascertain that the bismuth deposits were uniformly distributed across the whole surface of the glassy carbon substrate electrode. Comparative AFM measurements corroborated the above findings and additionally revealed a denser growth of smaller bismuth crystals over the surface of the substrate electrode in the presence of bromide ions, while the crystals were bigger but sparser in the absence of bromide ions in the modification solution.     

Surface of poly(ethylene terephthalate/isophthalate) copolyesters studied by atomic force microscopy

An atomic force microscope (AFM) operating in Tapping™ and contact modes has been used to study the surface topography and the molecular organization of poly(ethylene terephthalate) (PET) films containing 2% (PET‐2I) and 10% (PET‐10I) isophthalate, and of injection/blow molded bottles containing 2.6% (PET‐2.6I) and 10% isophthalate. Large‐scale (15‐μm × 15‐μm) AFM images have shown that both surfaces are fairly flat and heterogeneous in nature, often containing inclusions. Whereas the PET surface appears to be formed mainly by microfibrils, isophthalic acid (IPA) incorporation at the 2–10 mol % level gives the surface a granular appearance. The IPA‐containing PET surfaces are frequently coated by a lacelike film consisting of submicron “beads” joined together by filaments. These “strings of beads” form bundles and can also connect bundles. AFM images of PET‐2I closely resemble those generated for PET films. By contrast, the lacelike structure becomes a dominant feature of the PET‐10I surface. The level of inclusions observed on film surfaces appears to correlate with the levels of extractable oligomers present in the polymers. Nanometer‐scale AFM images of PET‐10I exhibit surfaces composed of short stacks of plates or rods, with 30–50‐nm voids or pores between these stacks. Whereas surface deposits of what we suggest is most likely an oligomer correlates with isophthalate concentration, we see no gross structural features in PET‐2I and PET‐10I that explain the observed improvement in gas diffusion barrier in these polymers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 750–762, 2001     

Segregation in granular materials and the direct measurement of surface forces using atomic force microscopy

It is known that one of the dominant forces controlling the macroscopic motion of particles is the cohesive force due to the presence of liquid bridges between particles. In a mixing process, this force directly impacts the degree of homogeneity achievable by the system. The work presented here provides a quantitative analysis of this relationship through concurrent direct measurements of surface forces due to moisture and blending/segregation experiments. Atomic force microscopy (AFM) was employed to measure the force required to remove the AFM's cantilever from the surface of a glass bead with varying degrees of surface moisture. Corresponding blending/segregation experiments were performed using the same materials and conditions to develop a correlation between the interparticle forces due to the liquid layer and the final state of a mixing process. The extent to which greater moisture content increased the interparticle surface forces was quantified, and it was observed that segregation decreases proportionately to increases in surface forces.     

In situ co-adsorption of arsenic and iron/manganese ions on raw clays

The use of clays as effective arsenic sorbents has been strongly limited due to their low pH_ZPC and cation active behaviour in aqueous systems at pH > 3.5. A simple Fe/Al/Mn pre-treatment can significantly improve their sorption affinity to oxyanions, including arsenites and arsenates. The dynamics of arsenic adsorption from groundwater is also controlled by dissolved Fe/Mn ions, which behave as promoters of As adsorption, or competitors to adsorption sites. Low grade calcinated kaolin (MT) and bentonite (BT) were used as clay sorbents. Arsenic adsorption on raw clays without presence of Fe/Mn ions is very slow and limited. During co-adsorption the Fe/Mn ions and As oxyanions were adsorbed together onto a sorbent surface. Both Mn and Fe particles demonstrated a good sorption affinity to the clay surface, but only Fe particles supported As adsorption considerably (80% of As were removed in Fe/As system, while < 30% only in the Mn/As system). The kinetics of co-adsorption compared to the use of Fe/Mn pre-modified sorbents indicated a more dynamic process, while all mechanisms corresponded to the first order run (k ≈ 9.10^− 6- 1.10^− 4 s^− 1). Arsenic was strongly stabilized in pre-modified sorbents.     

In situ transesterification of coconut oil using mixtures of methanol and tetrahydrofuran

The conventional biodiesel production method requires oil extraction followed by transesterification with methanol. The solubility of vegetable oils in methanol is low which decreases the overall rate of reaction. To eliminate the oil extraction step and improve the overall reaction rate, simultaneous extraction, esterification and transesterification were conducted by directly mixing methanol and tetrahydrofuran (THF) co-solvent and sulfuric acid catalyst with ground, desiccated coconut meat (copra) in a batch process and continuing the reaction until the system reached steady state. After separation of the mixture, yield was obtained by measuring the content of triglycerides, diglycerides and monoglycerides in the biodiesel phase. The yield increases with THF:methanol ratio, methanol:oil molar ratio and temperature. Within the range of conditions tested, the highest yield achieved was 96.7% at 60 °C, THF:methanol volume ratio of 0.4 and methanol:oil molar ratio of 60:1. The methanol:oil molar ratio is necessarily high in order to completely wet the copra mass, but is still lower than in previous studies by other researchers on in situ transesterification. Product assays show that the resulting biodiesel product is similar to conventionally produced coconut biodiesel. The results indicate that the in situ transesterification of copra using methanol/THF mixtures merits further study.     

Understanding of electrochemical and structural changes of polypyrrole/polyethylene glycol composite films in aqueous solution

Electrochemical monitoring of electrical and structural changes of both PPy and PPy–PEG films electrochemical deposited, in order to highlight if the structural stability offered by PEG has an influence on electrical properties and stability in aqueous solution over immersion time was investigated.Electrochemical analysis suggests that PPy–PEG film inserts cations easier than PPy film for a short immersion time probably due to ability of PEG to form complexes with metal cations.The FTIR spectra showed that the PEG incorporation decreases the rate of PPy overoxidation probably by restraining the electron release and by rendering O₂ inaccessible to PPy.Mott–Schottky analysis based on capacitance measurement reveal p-type conductance for both films.The in situ AFM analysis sustains electrochemical behaviour and has permitted elaboration of a model of PPy and PPy–PEG films behaviour during immersion in testing solution.