Electrochemical synthesis and characterization of poly-2-aminothiazole

2-Aminothiazole (2AT) was electrochemically polymerized on a Pt electrode using cyclic voltammetry (CV) technique from 0.01 M monomer containing 0.3 M ammonium oxalate solution. The high quality poly-2-aminothiazole (pAT) films with a light-brownish color were obtained on the Pt surface. The electrochemical behavior of the pAT-coated Pt electrode (Pt/pAT) was investigated in monomer-free 0.3 M ammonium oxalate solution by CV technique. The chemical structure characterization was investigated by UV–vis spectroscopy (UV–vis) and Fourier transform infrared spectroscopy (FTIR) techniques. The surface morphology of the polymer film was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface morphology studies showed that, a homogeneous and compact film was formed on the Pt surface. Further, thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) techniques were used to investigate the thermal properties of the polymer film. It was found that the thermal stability of the pAT film is relatively high. The solubility of the pAT was tested in common organic solvents as well as in acidic and basic solutions.     

Electrochemical impedance spectroscopy study of waterborne coatings film formation

In order to establish electrochemical impedance spectroscopy (EIS) as a viable quantitative method for characterization of latex film formation, three waterborne acrylate and styrene–acrylate polymer dispersions were periodically analyzed during a course of 2 weeks. Impedance spectra were fitted on the base of equivalent circuit consisting of a capacitor in parallel with a Warburg element representing film capacitance and the extent of ion diffusion through the film. Calculated EIS parameter values showed a decrease in Warburg diffusion over time, which is a result of particle coalescence and in agreement with the established theory of latex film formation. Atomic force microscopy (AFM) of the samples showed a smoothing of the surface and blurring of interparticle boundaries which confirmed that EIS can be used to study film formation of latex.     

Abrasion and nanoscratch in nanostructured epoxy coatings

A series of epoxy nanostructured coatings based on diglycidyl ether of bisphenol A (DGEBA) and an isophorone diamine crosslinker was prepared. Top‐down nanocomposites (3% nanofiller) were obtained by the mechanical dispersion of nanoalumina, silanized nanoalumina, and organomodified clays. Bottom‐up hybrids were instead achieved after the silanization of the DGEBA resin and after cocrosslinking with tetraethylorthosilicate through a self‐catalyzed sol–gel process. The curing process of the nanocomposites was studied by differential scanning calorimetry and suggested an overall increase in the crosslinking kinetics in the presence of nanoparticles. Other characterization included dynamic mechanical analysis, Buchholtz indentation hardness testing, and Taber abrasion testing. Finally, atomic force microscopy (AFM) techniques were used to study the surface morphology of the coatings and to produce nanoscratches. We concluded that, in the top‐down nanocomposites, there were minor changes in the surface hardness and a slight improvement in the abrasion resistance, whereas the nanoscratch resistance assessed by AFM tests showed significantly better performances in the hybrid coatings obtained through sol–gel chemistry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fabrication of efficient nanostructured Co3O4-Graphene bifunctional catalysts: Oxygen evolution,hydrogen evolution,and H2O2 sensing

Nanostructured Co₃O₄-graphene hybrid catalysts are fabricated by a one-step vacuum kinetic spray technique from microparticles of Co₃O₄ and graphite powders. The Co₃O₄-graphene hybrid catalysts with various Co₃O₄ contents are studied concerning the oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in 1.0 M KOH, as well as, H₂O₂ sensing in 0.1 M NaOH. We find that increasing graphene content in the hybrid catalysts results in an overall improvement of the OER electrocatalytic activity due to the enhancement in the charge transfer kinetics. The hybrid catalyst with 25 wt% Co₃O₄ reveals the optimum electrocatalytic activity toward the OER with the lowest overpotential (η) of 283 mV@ 10 mA cm⁻² and superior reaction kinetics with a low Tafel slope of 25 mV dec⁻¹. Besides, the OER stability at 50 mA cm⁻² for 50 h in 1.0 M KOH was verified. The hybrid catalyst with 50 wt% Co₃O₄ revealed the highest activity toward the HER with η of 108 mV@ 10 mA cm⁻², Tafel slope of 90 mV.dec⁻¹, and stability at 50 mA cm⁻² for nearly 30 h. Moreover, it reveals ultrahigh H₂O₂ amperometric detection with superior sensitivity of 18,110 μA mM⁻¹ cm⁻², linear detection range from 20 μM to 1 mM, and a limit of detection of 0.14 μM.     

CoSe2@NF双功能电催化剂用于高效碱性全解水

开发用于水分解的高效稳定、低成本非贵金属电催化剂，特别是在同一电解质中对阴极的析氢反应(HER)和阳极的析氧反应(OER)都具有高效作用的电催化剂是一项挑战。以六水合硝酸钴、尿素、氟化铵和硒粉为原料，采用水热和高温固相法在镍网上原位构筑了CoSe2@NF，采用XRD、XPS、SEM和TEM对CoSe2@NF进行物相分析和形貌表征，并在碱性电解液中对CoSe2@NF的电催化析氧和析氢性能进行了测试。结果表明，表面粗糙的串珠状纳米线结构极大地增加了CoSe2有效活性位点的数量。该催化电极在OER和HER中均表现出高而稳定的催化活性。将CoSe2@NF作为全解水槽的阴阳极，在1.6 V槽电压下即可产生10 mA/cm2的电流，并可在1.7 V的电压下稳定运行100 h。这项研究为全解水提供了一种经济有效的解决方案.     

Preparation and characterization of hybrid organic–inorganic epoxide‐based films and coatings prepared by the sol–gel process

Hybrid organic–inorganic coatings and free‐standing films were prepared and characterized. The hybrids were prepared from [3‐(glycidyloxy)propyl]trimethoxysilane, diethoxy[3‐(glycidyloxy)propyl]methylsilane, poly(oxypropylene)s of different molecular weights end‐capped with primary amino groups (Jeffamines D230, D400, and T403), and colloidal silica particles with hydrochloric acid as a catalyst for the sol–gel process and water/propan‐2‐ol mixtures as solvents. The structure evolution during the network formation was followed by NMR spectroscopy and small‐angle X‐ray scattering; the surface morphology was tested by atomic force microscopy. The influence of the reaction conditions (the organosilicon precursor, oligomeric amine, ratio of functional groups, and method of preparation) on the network buildup and product properties was studied and examined. The mechanical testing, based on stress–strain experiments, in combination with dynamic mechanical thermal analysis served as an effective instrument for the optimization of the reaction conditions for the preparation of products with desired properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 937–950, 2004     

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.     

Atomic force microscopy study of the photografting of glycidyl methacrylate onto HDPE and the microstructure of the grafted chains

This article presents an atomic force microscopy (AFM) study of the initial stage of the photografting of glycidyl methacrylate (GMA) onto high-density polyethylene (HDPE) surface and the microstructure of the grafted chains. The grafting was carried out in acetone, dichloromethane and tetrahydrofuran (THF), as well as without solvent. Granular structures were found on the surface of the samples grafted in the solvents. The height of the granules increased linearly with their diameter. Each granule was thought to be a single grafted chain with a highly branched (or superbranched) microstructure. The grafting density on HDPE was quite small when the grafting was carried out in the solvents. The grafted chains were more branched when grafting was carried out in THF than when the grafting was carried out in acetone and dichloromethane. The bulk (no solvent) grafting of GMA onto HDPE was much faster and more uniform than that carried out in the solvents. The thickness of the bulk grafted materials was a few nanometers after 30 s irradiation, and possibly, the grafting density was much higher and the grafted polymers were much less branched than those produced in solvent.     

A Study on Hydrophobic Surface Coatings with Abrasion Resistance Property

The aim of this study is to synthesize a hydrophobic surface coating with abrasion-resistant inorganic-organic hybrid materials. First, the copolymer of poly (MMA-co-MPTS)-colloid silica was synthesized by using the free radical polymerization of the methyl methacrylate (MMA) with γ-methacrylate propyltriethoxysilane (γ-MPTS). Next, the copolymer was hydrolyzed with tetraethoxylsilane (TEOS), fluoroalkylsilane (FAS), and colloid silica in the weak acid condition by a sol-gel process to obtain the surface coatings of hybrid material of poly (MMA-co-MPTS)-colloid silica. Finally, the effects of the colloid silica content on the optical properties, abrasion resistance, and morphology of the hybrid surface coatings were discussed in this study.     

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.     

Influence of magnetic field on hydrogen reduction and co-reduction in the Cu/CuSO4 system

The effects of an applied magnetic field of up to 5 T on hydrogen evolution and cathodic overpotential were studied for H₂SO₄ and an acidic Cu/CuSO₄ system. Cyclic voltammetry, potentiostatic and galvanostatic deposition as well as electrochemical noise measurements were used. The magnetic field simultaneously increases the rate of hydrogen evolution and modifies the hydrogen bubble size. The periodicity of bubble release from a microelectrode is strongly influenced by the field, which may change the characteristic frequency or make it aperiodic, depending on the field orientation relative to buoyancy. The magnetic field stabilizes a bubble growing on a microelectrode, especially at high current densities. For example, bubble volume increases by a factor four in 1.5 T when the Lorentz force acts downwards. The noise spectra around 1 kHz are characteristic of a coalescence phenomenon. Hydrogen co-reduction with copper was studied by scanning electron microscopy and the current efficiency was measured with a quartz crystal microbalance; at −1.0 V it decreases from 95% to 75% in a field of 1.5 T. Bubble release is no longer periodic, but the noise spectrum has a characteristic shape depending on whether the current density is greater than, equal to or less than the diffusion-limited copper current. The field reduces the roughness of the copper deposit, but the current efficiency can be maximized by controlling the system galvanostatically, which allows a high copper deposition rate at overpotential lower than 0.5 V in the applied field, with smooth deposit quality.     

Using steered molecular dynamics simulations and single-molecule force spectroscopy to guide the rational design of biomimetic modular polymeric materials

This article describes results on using steered molecular dynamics (SMD) simulations and experimental single-molecule force spectroscopy (SMFS) to investigate the relationship between hydrogen bonding and mechanical stability of a series of homodimeric β-sheet mimics. The dimers consisting of 4, 6, and 8 H-bonding sites were modeled in explicit chloroform solvent and the rupture force was studied using constant velocity SMD. The role of solvent structuring on the conformation of the dimers was analyzed and showed no significant contribution of chloroform molecules in the rupture event. The simulated stability of the dimers was validated by force data obtained with atomic force microscopy (AFM)-based SMFS in toluene. The computational model for the 8H dimer also offered insight into a possible mismatched dimer intermediate that may contribute to the lower than expected mechanical stability observed by single-molecule AFM force studies. In addition, atomic level analysis of the rupture mechanism verified the dependence of mechanical strength on pulling trajectory due to the directional nature of chemical bonding under an applied force. The knowledge gained from this basic study will be used to guide further design of modular polymers having folded nanostructures through strategic programming of weak, non-covalent interactions into polymer backbones.     

Solvent effects on the elasticity of polysaccharide molecules in disordered and ordered states by single-molecule force spectroscopy

Single-molecule force spectroscopy, especially as implemented on an atomic force microscopy (AFM) platform is unique in its ability to apply small (F<10 pN) and large (F>1000 pN) stretching forces to individual polymer chains and in this way examines their elasticity and also reports force-induced conformational transitions in whole polymers and in their building blocks. In this paper, we briefly review recent applications of single-molecule force spectroscopy to the study of polysaccharides elasticity. We provide examples illustrating AFM measurements of solvent effects on the hydrogen bonding and the elasticity of individual polysaccharides and how molecular dynamics simulation can aid the interpretation of AFM results. We also discuss the use of single-molecule force spectroscopy in exploring ordered secondary structures of individual polysaccharide chains and their multi-strand complexes.     

Poly(glutamic acid) nanofibre modified glassy carbon electrode: Characterization by atomic force microscopy, voltammetry and electrochemical impedance

Glassy carbon electrodes (GCE) were modified with poly(glutamic acid) acid films prepared using three different procedures: glutamic acid monomer electropolymerization (MONO), evaporation of poly(glutamic acid) (PAG) and evaporation of a mixture of poly(glutamic acid)/glutaraldehyde (PAG/GLU). All three films showed good adherence to the electrode surface. The performance of the modified GCE was investigated by cyclic voltammetry and differential pulse voltammetry, and the films were characterized by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). The three poly(glutamic acid) modified GCEs were tested using the electrochemical oxidation of ascorbic acid and a decrease of the overpotential and the improvement of the oxidation peak current was observed. The PAG modified electrode surfaces gave the best results. AFM morphological images showed a polymeric network film formed by well-defined nanofibres that may undergo extensive swelling in solution, allowing an easier electron transfer and higher oxidation peaks.     

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.     

Electrophoretic deposition of fiber hydroxyapatite/titania nanocomposite coatings

Hydroxyapatite/titania nanocomposite coatings were electrophoretically deposited from ethanolic suspensions of titania and fiber shaped hydroxyapatite (FHA) nanoparticles. Triethanolamine (TEA) was used to enhance the colloidal stability of particles in suspensions. Electrophoretic deposition (EPD) was performed using the suspensions with different concentrations (wt%) of titania/FHA particles. EPD rate decreased more rapidly with time for suspensions with higher wt% of FHA due to the higher voltage drop over the deposits shaped from them. Stacking of long FHA particles on the substrate during EPD resulted in the formation of coarse pores in the deposits. It was found that titania nanoparticles can more efficiently infiltrate through and fill the pores in TEA containing suspensions due to the stronger electrostatic repulsion force between pore walls (FHA) and titania nanoparticles in them. The coatings deposited from the suspensions with 50 wt% of FHA or more did not crack during drying due to the significant reinforcement action provided by high wt% of FHA in them. Nanocomposite coatings deposited from TEA containing (2 mL/L) suspensions with 50 and 75 wt% of FHA had the best corrosion resistance in simulated body fluid (SBF) solution due to their crack-free microstructure and efficiently filled pores.     

Electrochemical preparation and characterization of nickel and zinc-modified poly-2-aminothiazole films on mild steel surface and their corrosion inhibition performance

Poly-2-aminothiazole (pAT) was electrochemically synthesized on a mild steel (MS) specimen from 0.3 M aqueous ammonium oxalate solution containing 0.01 M 2-aminothiazole (2-AT) using cyclic voltammetry technique. The synthesized polymer film was then modified by electrodeposition of 100 μg cm⁻² Ni (MS/pAT–Ni) and Zn (MS/pAT–Zn) on top of the polymer surface. The surface morphologies of the polymer films were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The elemental analysis of the surface films was performed by energy dispersive X-ray spectroscopy (EDX). The effectiveness of the coatings in preventing corrosion of MS in 3.5% NaCl solution was assessed using electrochemical techniques. It was found that the obtained coatings were adherent to the steel surface. The pAT film provided a good corrosion protection against the attack of corrosive environment. Moreover, the modification of pAT film by deposition of Ni and Zn on top of the polymer surface significantly enhances the corrosion protection performance of the polymer film by exhibiting an improved barrier effect against the attack of corrosive environment. The surface morphologies and protection ability of the layers were found to be dependent on the type of deposited metal.     

Electrochemical preparation and characterization of Ni/SiC compositionally graded multilayered coatings

In our study, Ni/SiC functionally graded coatings have been obtained by electrochemical deposition of silicon carbide microparticles (mean diameter 2 μm) from nickel Watts baths with different concentrations of SiC particles in solution. The SiC particles were characterized by electroacustics technique in order to determine zeta potential and particle size. Moreover, the effect of the concentration of SiC particles in solution on the amount of SiC deposited in the nickel layer was investigated. Further experiments showed that the degree of particle incorporation provoked changes in the texture of the nickel matrix. The characterization of the coatings proved that the Ni/SiC graded composite coatings were bright and compact, presented good adhesion and improved the hardness and wear resistance of pure nickel electrodeposits.     

Nanotribology at single crystal electrodes: Influence of ionic adsorbates on friction forces studied with AFM

We present friction force measurements on Au(1 1 1) single crystal electrode surfaces performed under electrochemical conditions using an atomic force microscope (AFM). At monoatomic steps friction is increased in both scan directions. In 0.05 M sulfuric acid an increase of friction is observed with the increase of adsorbed sulfate. Friction force increases non-linearly with load. Cu UPD also increases friction in presence of sulfate. However, in presence of 4 × 10⁻⁴ M chloride friction is much smaller for all deposited Cu coverages - ranging from a submonolayer up to bulk copper compared to the solution without chloride. After dissolution of bulk copper clusters deposited on Au(1 1 1) we observed an area with higher friction forces due to the formation of an alloy between gold and copper.     

Surface,tribological, and mechanical characterization of synthetic skins for tribological applications in cosmetic science

Synthetic skin as an ideal human‐tissue substitute is needed for the research and assessment of hair‐ and skin‐care products. In this study, a systematic study was carried out of the surface, tribological, and mechanical properties of two synthetic skins and rat skin with and without skin‐cream treatment with scanning electron microscopy, atomic force microscopy, and a nanoindenter. The film thickness, adhesive force, coefficient of friction, surface roughness, and contact angle of the two synthetic skins and rat skin were comparable. The hardness of one synthetic skin was more similar to rat skin. After treatment with skin cream, the trends of the properties of the two synthetic skins and rat skin were similar. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011