Investigation of morphological and electrical properties of the PMMA coating upon exposure to UV irradiation based on AFM studies

The objective of study was to investigate the influence of UV irradiation on morphological changes of a polymeric surface and its electrical properties. In the presented investigation thin poly(methyl methacrylate) (PMMA) film was applied onto iron substrate by solution casting method. UV-C irradiation in range of 200–280 nm was used as a deteriorative factor to induce polymer degradation. Atomic force microscopy (AFM) method was employed to study surface topography of the PMMA coatings before and after exposure to UV-illumination. Photo-induced changes in the polymer surface taking form of microcracks were illustrated by AFM images. In order to support results obtained with AFM method, electrochemical impedance spectroscopy (EIS) measurements were conducted. The authors chose this technique to confirm whether the changes on UV-exposed PMMA surface observed on AFM images could indicate potential sites of the polymer coating long before serious damage could occur. Both methods EIS and AFM were used in order to provide information about durability of PMMA film.     

Study on the adsorption of poly(o-ethoxyaniline) nanostructured films using atomic force microscopy

Nanostructured films of poly(o-ethoxyaniline) (POEA) were studied by atomic force microscopy (AFM), which indicated a globular morphology for films containing one or more layers of POEA. Consistent with the nucleation and growth model for the adsorption process, the mean roughness and fractal dimension were found to increase with the time of adsorption and with the number of POEA layers in the initial stages of adsorption, reached maximum values and then decreased after 10 min of adsorption or after deposition of five POEA layers. Such behavior has been explained in terms of the decrease in the film irregularities, with voids being filled with polymeric material leading to smoother surfaces.     

Investigation of electrode composition of polymer fuel cells by electrochemical impedance spectroscopy

In order to optimize the electrode composition and performance of Polymer Fuel Cells and to reduce the production cost of membrane electrode assemblies (MEAs), different MEAs using different catalyst powders, carbon supported and unsupported catalysts with different proton conducting electrolyte powder (Nafion) content were produced by using a dry powder spraying technique developed at German Aerospace Research Center (DLR, Deutsches Zentrum fuer Luft- und Raumfahrt). The electrochemical characterization was performed by recording current-voltage curves and electrochemical impedance spectra (EIS) in the galvanostatic mode of operation at 500 mA cm⁻². The evaluation of the measured impedance spectra with an adequate equivalent circuit shows that the cathode of the fuel cell is very sensitive to the electrode composition whereas the contribution of the anode is very small and invariant to the electrode composition. Furthermore, it could be shown for the first time using electrolyte powder in the electrodes that the charge transfer of the cathode decreasing monotonically with increasing electrolyte content in the cathode. These findings suggest that with increasing electrolyte content in the electrodes, in particular in the cathode, the utilization degree of the catalyst increasing linearly with increasing electrolyte content in the electrode.     

Metallo-functionalized first-generation salicylaldimine poly(propylenimine) tetraamine dendrimers: Electrochemical study and atomic force microscopy imaging

The adsorption and the redox processes of two first-generation salicylaldiamine dendritic ligands and their copper, cobalt and nickel metallo-functionalized complexes have been studied at two types of carbon electrode surface. Glassy carbon (GC) was used in an electrochemistry study and highly oriented pyrolitic graphite (HOPG) in ex situ atomic force microscopy (AFM) imaging. All salicylaldimine ligands and their metallo-functionalized complexes adsorb on the surface of the HOPG electrode, resulting in the formation of nanoclusters and films, which vary between 0.9 and 6 nm in size, depending on the metallo-functionalized salicylaldimine dendrimer chemical composition and solution concentration. Differential pulse voltammetry of the surface-confined films has shown that the anodic reactions observed correspond to the oxidation of the hydroxyl groups present in the ligand structure of all compounds. However, by following the changes in peak currents, potentials and width at half height it has been shown that destabilization of the ligand internal structure occurred in the metallo-functionalized complexes depending on the metal involved. The electrochemical behaviour of the surface-confined films observed in buffer solution was related to the morphology, obtained by AFM, of the immobilised first-generation salicylaldiamine dendritic ligands and corresponding salicylaldimine metallo-functionalized complexes.     

Biodegradable Blends Prepared from Polycaprolactone and Poly(glutamic acid): Structure,Thermal Properties,and Biodegradability

Biodegradable polycaprolactone/poly(glutamic acid) (PCL/PGA) blends were prepared by a melt blending method. Additionally, acrylic acid-grafted polycaprolactone (PCL-g-AA) was studied as an alternative to PCL. The samples were characterized using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), an Instron mechanical tester, and scanning electron microscopy (SEM). Because of poor compatibility between PCL and PGA, the mechanical properties of PCL/PGA blends were worse than of PCL alone. The PCL-g-AA/PGA blends had obviously improved mechanical properties over PCL/PGA ones, and the former provided a plateau tensile strength at break when the PGA content was up to 20 wt%. Biodegradation tests of blends were also conducted in a soil environment; the results showed that the mass of blends declined by about the PGA content within 4 weeks.     

Direct analysis of annealing of nodular crystals in isotactic polypropylene by atomic force microscopy, and its correlation with calorimetric data

The process of isothermal annealing of nodular monoclinic crystals of isotactic polypropylene (iPP) was analyzed by atomic force microscopy (AFM) and temperature-modulated differential scanning calorimetry (TMDSC). Initially nodular and mesomorphic domains were obtained by controlled melt-crystallization at high cooling rate. Subsequent heating triggers transition from mesomorphic to monoclinic structure, and melting of unstable nodules. Annealing allows re-crystallization, which is recognized by enlargement of domains from initially about 20 nm to about 35 and 55 nm after annealing at 393 and 433 K, respectively. Furthermore, the re-crystallization process is connected with a slight change of the aspect ratio of crystals. The isothermal re-crystallization of the liquid is superimposed by aggregation of crystals, to yield blocky, and string-like objects. The direct analysis of structure on isothermal annealing by AFM is for the first time compared with the isothermal decrease of the apparent specific heat capacity, or change of enthalpy, monitored by TMDSC. The apparent specific heat capacity decreases during annealing with an identical non-linear time dependence as the directly observed growth of the crystal size. Analysis of the annealing processes at different temperatures yields proportionality between the increase of the crystal size and the reduction of the apparent specific heat capacity.     

Electrochemical impedance spectroscopy of lead(II) ion-selective solid-state membranes

Silver sulphide/lead sulphide membranes were studied using electrochemical impedance spectroscopy. The influence of the electrolyte concentration and the membrane thickness were evaluated. The complex impedance plots have shown two capacitive loops: one at high frequency range, related with the charge transfer resistance at the interface membrane-Ag and a second one at low frequency range, associated with the diffusion process through the membrane. A simple model was used to take into account the experimental results: the changes of the potential with the time and the electrolyte concentration; the changes of the charge transfer resistance and the diffusion resistance with the electrolyte concentration. An empirical equation was used to calculate the diffusion coefficient of Ag⁺ inside the membrane.     

Electrochemical characterization of poly(eriochrome black T) modified glassy carbon electrode and its application to simultaneous determination of dopamine, ascorbic acid and uric acid

A polymerized film of eriochrome black T (EBT) was prepared on the surface of a glassy carbon (GC) electrode in alkaline solution by cyclic voltammetry (CV). The redox response of the poly(EBT) film at the GC electrode appeared in a couple of redox peak in 0.1 M hydrochloride and the pH dependent peak potential was −55.1 mV/pH which was close to the Nernst behavior. The poly(EBT) film-coated GC electrode exhibited excellent electrocatalytic activity towards the oxidations of dopamine (DA), ascorbic acid (AA) and uric acid (UA) in 0.05 mM phosphate buffer solution (pH 4.0) and lowered the overpotential for oxidation of DA. The polymer film modified GC electrode conspicuously enhanced the redox currents of DA, AA and UA, and could sensitively and separately determine DA at its low concentration (0.1 μM) in the presence of 4000 and 700 times higher concentrations of AA and UA, respectively. The separations of anodic peak potentials of DA-AA and UA-DA reached 210 mV and 170 mV, respectively, by cyclic voltammetry. Using differential pulse voltammetry, the calibration curves for DA, AA and UA were obtained over the range of 0.1-200 μM, 0.15-1 mM and 10-130 μM, respectively. With good selectivity and sensitivity, the present method provides a simple method for selective detection of DA, AA and UA in biological samples.     

Corrosion behavior of different alloys exposed to continuous flowing seawater by electrochemical impedance spectroscopy (EIS)

The corrosion of four types of alloys, under a dynamic condition, has been studied in continuous fresh seawater system using electrochemical impedance spectroscopy (EIS) technique. The materials used in this study were stainless steel 304, Cu-Ni 70-30, Hastelloy G-30, and titanium. The total exposure time of the test was 180 days, in continuous fresh seawater of the Gulf in Kuwait. The EIS tests were carried out by using EG&G software and hardware instrument. Electrochemical parameters such as the polarization resistance (R_P), solution resistance (R_Sol), and the double layer capacitance (C_dL) of these alloys were determined. Then the obtained EIS parameters were used to study the effect of the seasonal change of the Gulf seawater on the corrosion behavior of the tested materials. All the obtained EIS parameters showed that the seasonal changes of the Gulf seawater have a significant effect on controlling the rate of the formation of the marine bio-film on the surface of tested materials. Consequently, the corrosion behavior of the materials tends to vary as a function of the rate formation of the marine bio-film on the surface of tested materials.     

Physical evaluation of pure zein films by atomic force microscopy and thermal mechanical analysis

Biodegradable edible films can be made from corn protein, α-zein. Pure zein films are cast from an organic solution of α-zein. This report outlines the surface conditions of such pure zein films. First, the transition temperature, T _t′ of the pure zein film was measured with a thermomechanical analyzer. T _t was between 167.0 and 172.7°C. The thermal elongation of the films depended on the drying conditions used during film preparation. Second, the surface microstructure of pure zein films, produced under several different drying conditions, was observed by atomic force microscopy. The surface had a morphology that showed depressions either with acutely (90–120°) or obtusely (121–180°) angled features depending upon the drying conditions. On the other hand, the surface microstructure after thermal elongation analysis appeared to have a pattern of projections that was repeated every 25 nm. Third, we measured the contact angle of the pure zein films. We found a correlation between surface microstructure and contact angle. Pure zein films with projections smaller than 200 nm in base diameter on the surface had a high contact angle (>70°).     

The ultrastructure of spruce kraft pulps studied by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS)

Surface properties of spruce (Picea abies) kraft pulps cooked for different times and further OD₀E₁D₁E₂D₂-bleached were investigated with atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). A rough correlation between the increasing relative amount of the fibrillar surface structure in AFM images and increasing O/C atomic ratio in XPS-spectra was found with proceeding delignification. At the end of cooking (120 min) only about 1/3 of the fibre surface consisted of cellulose. The detailed analysis of the relative peak areas of the different C1s components in the XPS-spectra indicated that the granules at the beginning of cooking at 170 °C consisted mainly of lignin and extractives. The analysis also showed that different steps of the bleaching sequence were quite specific in removing structural components. Furthermore, the lignin removal was shown not to result automatically in increased fraction of exposed cellulose surface, but could also lead in increased relative amount of surface extractives. Evidence for the high surface content of hemicelluloses for the D2-stage sample was observed. Hemicelluloses with both fibrillar and amorphous morphology were found to be present.     

Crystal melting and its kinetics on poly(ethylene oxide) by in situ atomic force microscopy

The process of melting in poly(ethylene oxide) (PEO) is followed in real-time at elevated temperatures by atomic force microscopy (AFM) using a simple hot stage apparatus. AFM imaging of the morphology above the onset of melting revealed the dynamics of a complex melting process. The observed melting behavior of PEO is associated with the existence of separate dominant and subsidiary morphological entities. The morphological observations revealed that the melting process is not explained by a mechanism of crystal reorganization (melting-recrystallization-remelting or crystal thickening. The kinetic data shows that the crystal dimensions decrease proportional to time indicating a nucleation controlled melting process. The crystals melt instantaneously on heating and reveal a spread in the rates of melting of the radial {120} faces. This variation in rate of retrogression of the crystals is assumed to be related to a lamellar thickness distribution of the melt grown crystals.     

Poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes for the electrochemical detection of copper(II)

Poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes obtained by electropolymerization of 2-amino-4-thiazoleacetic acid, were used for the voltammetric determination of copper ions. The voltammetric response of copper ions at poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes was evaluated by differential pulse stripping voltammetry. The peak currents were linearly dependent on the concentrations of the copper ions in the range from 7.0 × 10⁻⁷ M to 5.0 × 10⁻⁵ M, with a coefficiency of 0.9987. The detection limit is 5.0 × 10⁻¹⁰ M calculated for a signal-to-noise ratio of 3 (S/N = 3). And it could be used for the simultaneous determination of copper and cadmium ions. The proposed method was successfully applied to the determination of copper ions in natural water. The concentration of Cu²⁺ was calculated to be 2.0 × 10⁻⁵ M by standard addition method. The recovery rate was 94%.     

Covalent Immobilization of Tyrosinase on Electrospun Polyacrylonitrile/Polyurethane/Poly(m-anthranilic acid) Nanofibers: An Electrochemical Impedance Study

Polyacrylonitrile/polyurethane/poly(m-anthranilic acid) nanofibers were fabricated by electrospinning. Tyrosinase immobilization was performed by EDC/N-hydroxyl succinimide activation. Covalent binding of tyrosinase onto nanofibers was confirmed by Fourier transform infrared-attenuated total reflectance, and bicinchoninic acid assay revealed the amount of enzyme. Nanofiber morphology and composition were characterized by scanning electron microscopy/energy-dispersive X-ray spectroscopy (EDX). Nanofibers became smoother and thicker after tyrosinase immobilization. Effects of enzyme on nanofibers were investigated by electrochemical impedance spectroscopy and the data were fitted to equivalent electrical circuit model. EDX-mapping showed uniform distribution of enzyme. The solution resistance and charge transfer resistance of nanofibers decreased after enzyme immobilization.     

Nanosecond T-Jump Experiment in Poly(glutamic acid): A Circular Dichroism Study

Poly(glutamic acid) has been studied with a nanosecond T-jump experiment. A new experimental set-up based on the frequency-quadrupling of an 82 MHz Titanium-Sapphire laser allows rapid CD measurements to be performed. Combining time-resolved absorption and circular dichroism at 204 and 220 nm, we are able to measure precisely the unfolding relaxation time as well as the helical fraction evolution. We show that only CD at 220 nm is relevant to observe the unfolding of an alpha helix whereas no change is observed for CD at 204 nm. Conversely, both absorptions yield information on the dynamics of the process.     

Study on the Crystallization Kinetic and Characterization of Poly(lactic acid) and Poly(vinyl alcohol) Blends

In this study, poly(lactic acid) (PLA) and poly(vinyl alcohol) (PVA) blends, with PLA/PVA mass ratios of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50, and 40/60, were prepared by means of the melt blending method. The result of torque measurements and thermal gravimtric analysis tests showed that the addition of PLA can decrease the melt viscosity of PVA and that the second degradation step of PVA nearly disappeared for the PLA₈₀/PVA₂₀ blend. The absorbance peaks of the carbonyl group and the hydroxyl group in the Fourier transform infrared spectra of PLA/PVA blends had significant shifts to lower wave numbers, indicating that there were interactions between these two groups. Combined with the result of the differential scanning calorimetry curves, this interaction would be favorable for improving miscibility. The X-ray diffraction patterns and the polarized light microscope (PLM) micrographs showed that PVA can serve as a nucleating agent to promote the crystallization of PLA in PLA/PVA blends. Moreover, the PLA₈₀/PVA₂₀ blend gave the highest growth rate of PLA spherulite.     

Electrochemical, EIS and AFM characterisation of biosensors: Trioxysilane sol-gel encapsulated glucose oxidase with two different redox mediators

Sol-gel encapsulated glucose oxidase (GOx) enzyme electrodes based on carbon film resistors with chemically deposited copper hexacyanoferrate (CuHCF) or poly(neutral red) (PNR), made by electrochemical polymerisation, as redox mediator have been developed and characterised using cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy. The sol-gel was prepared using three different trioxysilanes: 3-aminopropyl-triethoxysilane (APTOS), 3-glycidoxypropyl-trimethoxysilane (GOPMOS) and methyltrimethoxysilane (MTMOS), without alcohol addition, and alcohol formed during the hydrolysis of the precursor compounds was removed. The best sensitivity, ∼60 nA mM⁻¹, for glucose and limit of detection (2-40 μM, depending on the sol-gel precursor) were obtained when PNR was used as a mediator, but the linear range (50-600 μM) was two to four times lower than that at CuHCF mediated biosensors, using an operating potential of +0.05 V at CuHCF or −0.25 V versus saturated calomel electrode (SCE) at PNR mediated electrodes. The stability of the sensor depended on the sol-gel morphology and was 2 months testing the biosensor every day, while the storability was at least 4 months in the case of GOPMOS, the sensors being kept in buffer at +4 °C.     

Electrocatalytic oxidation of thioglycolic acid at carbon paste electrode modified with cobalt phthalocyanine: application as a potentiometric sensor

The voltammetric behavior of thioglycolic acid (TGA) was studied at a carbon paste electrode modified with cobalt phthalocyanine (CoPc). The CoPc-modified electrode shows high electrocatalytic activity toward oxidation of TGA, lowering substantially the overpotential of anodic reaction. Results of the cyclic voltammetry show that TGA undergoes a two-step oxidation (each step with one electron) resulting the dimer of thiol. Enhancement of the rate of electron transfer results in a near-Nernstian behavior of modified electrode to the concentration of TGA and makes it as a suitable potentiometric sensor for the detection of this compound. This electrode shows a near-Nernstian response in a wide linear range of the concentration TGA (4 orders of magnitude). The modified electrode was used successfully for the determination of TGA and its salts in hair-treatment products and also in culture media. The modified electrode exhibited a fast response time (<10 s), very good stability, and had an extended lifetime.     

Preparation and characterization of reinforced poly(vinyl alcohol) films by a nanostructured,chiral, L-leucine based poly(amide-imide)/ZrO2 nanocomposite through a green method

In the present investigation, at first, the surface of ZrO₂ nanoparticles was modified with a bioactive and biocompatible diacid based on leucine amino acid as a coupling agent. The grafting of diacid on the surface of ZrO₂ was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis. Then, the synthesis of poly(amide-imide)/ZrO₂ nanocomposite (PAI/ZrO₂ NC) was performed through ultrasonic technique. The obtained NCs demonstrated good thermal stability. Field emission scanning electron microscopy and transmission electron microscopy analysis showed that the average diameter of NP was around 15–20 nm. Finally, the resulting NC, was used as a nano-filler and was incorporated into the poly(vinyl alcohol) (PVA) in order to improve its mechanical and thermal properties. The PVA/PAI–ZrO₂ NC films were characterized by different techniques. The data indicated that the thermal and mechanical properties of the PVA/PAI–ZrO₂ NC were enhanced. It was attributed to the good dispersion of filler into the PVA matrix as a result of hydrogen bonding.