Characterization of chemical heterogeneity in polymer systems using hydrolysis and tapping‐mode atomic force microscopy

Characterization of polymer coatings microstructure is critical to the fundamental understanding of the corrosion of coated metals. An approach for mapping the chemical heterogeneity of a polymer system using chemical modification and tapping‐mode atomic force microscopy (TMAFM) is demonstrated. This approach is based on the selective degradation of one of the phases in a multiphase polymer blend system and the ability of TMAFM to provide nanoscale lateral information about the different phases in the polymer system. Films made of a 70:30 polyethyl acrylate/polystyrene (PEA/PS) blend were exposed to a hydrolytic acidic environment and analyzed using TMAFM. Pits were observed to form in the PEA/PS blend films, and this degradation behavior was similar to that of the PEA material. Using these results, the domains in the 70:30 blend were identified as the PS‐rich regions and the matrix as the PEA‐rich region. This conclusion was confirmed by Fourier transform infrared‐attenuated total reflection analyses that revealed the hydrolysis of the PEA material. TMAFM phase imaging was also used to follow pit growth of the blend as a function of exposure time. The usefulness of the chemical modification/AFM imaging approach in understanding the degradation process of a coating film is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1460–1470, 2001     

SiOxNy thin films with variable refraction index: Microstructural, chemical and mechanical properties

In this work amorphous silicon oxynitride films with similar composition (ca. Si_0.40N_0.45O_0.10) were deposited by reactive magnetron sputtering from a pure Si target under different N₂-Ar mixtures. Rutherford backscattering (RBS) studies revealed that the coatings presented similar composition but different density. The mechanical properties evaluated by nanoindentation show also a dependence on the deposition conditions that does not correlate with a change in composition. An increase in nitrogen content in the gas phase results in a decrease of hardness and Young's modulus.The microstructural study by high resolution scanning electron microscopy (SEM-FEG) on non-metalized samples allowed the detection of a close porosity in the form of nano-voids (3-15 nm in size), particularly in the coatings prepared under pure N₂ gas. It has been shown how the presence of the close porosity allows tuning the refraction index of the films in a wide range of values without modifying significantly the chemical, thermal and mechanical stability of the film.     

Scratching behavior of elastomeric poly(dimethylsiloxane) coatings

Scratch testing has been performed on elastomeric poly(dimethylsiloxane) (PDMS) coatings on stainless steel with a spherical indenter. The friction coefficient (horizontal‐to‐normal force ratio) during scratching decreases with increasing normal load. This result can be explained by assuming that during scratching the contact area is determined by elastic deformation and the horizontal force is proportional to the contact area. With increasing driving speed, the friction coefficient increases, but the rate of increase decreases; this suggests that the scratching of the PDMS coating is a rate process and that the viscoelastic property of the coating influences its frictional behavior. Below a critical normal load, which increases with the coating thickness, the PDMS coating recovers elastically after being scratched so that there are no scratch marks left behind. Above the critical normal load, the coating is damaged by a combination of delamination at the coating/substrate interface and through‐thickness cracking. When the coating is damaged, there is an increase in the friction coefficient, and the friction force displays significant fluctuations. Furthermore, the critical normal load increases with the driving speed; this implies that time is needed to nucleate damage. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1530–1537, 2002     

Electrophoreted Zn-TiO2-ZnO nanocomposite coating films for photocatalytic degradation of 2-chlorophenol

TiO₂-ZnO nano-powders with different TiO₂/ZnO ratios have been synthesized by hydrothermal method. Nanocomposite coating films consisting of TiO₂-ZnO and Zn with thickness of 20 μm have been electrophoreted on steel plates by rapid plating from a ZnO-based alkaline bath. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis were used to investigate the structure, the size distribution, and the composition of prepared nano-powders and plated materials. The effect of the operating parameters such as powder contents, pH and current density on the electrophoresis process has been investigated and optimum conditions of coating process were determined. Corrosion properties of plated samples have been studied by salt spray test. The catalytic activity of the prepared nanocomposite Zn-TiO₂-ZnO films for the photocatalytic degradation of 2-chlorophenol (2-CP) was measured.     

Polymerization kinetics and microstructure of waterborne acrylic/alkyd nanocomposites synthesized by miniemulsion

Waterborne acrylic‐alkyd nanocomposites are expected to combine the positive properties of alkyd resins and acrylic polymers. In this work, the kinetics of the miniemulsion polymerization used to synthesize these nanocomposites and the effect of the process variables on the polymer architecture and particle morphology was investigated. It was found that resin hydrophobicity and the type of initiator strongly affected the microstructure of these materials. The mechanisms responsible for these effects were discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4871–4885, 2009     

Synthesis of UV‐cured acrylic–silica hybrid nanocomposites from dendritic acrylic oligomer and acrylic‐functionalized silica

An acrylic–silica hybrid polymeric nanocomposite, comprising well‐distributed silica nanoparticles in acrylic matrix, has been synthesized at a markedly rapid rate from a dendritic acrylic oligomer (DAO) and an acrylic‐functionalized silica (A‐silica) via UV‐curing. A‐silica was made by functioning colloidal silica nanoparticles with 3‐methacryloxypropyltrimethoxysilane (MATMS) and DAO was formed by reacting 1,5‐diamino‐2‐methylpentane (MPMDA) with trimethylopropane triacrylate (TMPTA). The MATMS has been found either doubly or singly bonded to silica nanoparticles but not triply bonded, and the inclusion of MATMS into the siloxane network structure increases the size of silica nanoparticles. The well distribution of A‐silica and its good compatibility with DAO cause an increase in T_d of the acrylic–silica hybrid material. Silica nanoparticles are too small to cause any significant light scattering, and do not have deleterious effects on transparency. The “hybrid‐on‐polyethylene terephathalate” films exhibited satisfactory hardness and surface roughness because of silica nanoparticles. The preparation as well as the characterization of the constituting species and the final hybrid material are described in detail. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8149–8158, 2008     

Characterization of bilayer coatings of TiN/ZrN grown using pulsed arc PAPVD

Nitride coatings have been used to increase hardness and to improve the wear and corrosion resistance of structural materials. Coatings of TiN/ZrN were grown on stainless steel substrates using a physical vapour deposition system assisted by pulsed arc plasma (PAPVD). The coatings have been characterized by X-ray diffraction (XRD) in order to identify the present phases of the films, microstrain level generated, crystallite size and the variation of the lattice parameter. The results showed plane orientations (1 1 1) and (2 0 0) in both TiN and ZrN films. Morphology surface analysis of the samples were performed using a scanning probe microscope to characterize the grain size and roughness in the mode of the atomic force microscopy (AFM) hence it was observed that the root-mean-squared (rms) roughness for ZrN is smaller than for TiN. Besides elastic and friction properties of the films were characterized qualitatively, and then, they were compared with those of the substrates by using force modulation microscopy (FMM) and lateral force microscopy (LFM) modes. In addition, an elemental analysis of the samples was realized by means of energy dispersive spectroscopy (EDS). Both, XRD and AFM results are given as a function of the number of shots. Chemical states of the TiN and ZrN films were determined by X-ray photoelectron spectroscopy (XPS).     

Poly(vinylpyrrolidone)‐based films grown on copper surfaces

The influence of molecular weight and the amount of the poly(vinylpyrrolidone) (PVP) on the growth of poly(vinylpyrrolidone)–based films on copper surfaces was studied by electrochemical, infrared and electronic spectroscopy, and thermogravimetric methods. Complex polymer/metal ions were deposited onto a copper surface, as the result of the electrochemically generated reaction of copper cations with PVP and SCN^?, in sulfuric acid media. Spontaneous film growth on copper surfaces was generated and characterized as a Cu(II)/PVP/SCN^? complex. Infrared spectra and thermal gravimetric curves of the films generated at + 0.7 V were compared with the chemically synthesized complex, and show the same patterns. The oxidation process can be described as: Cu(0)→Cu(I) and Cu(I)→Cu(II), and the copper complex formed at more positive potentials was characterized as Cu(II)/PVP/SCN^?, with copper bonded to the oxygen atom of PVP and thiocyanate ligand N‐linked. This study focuses on the complex formation on a copper surface in acid media and its characterization through electrochemical and spontaneously generated reactions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2206–2214, 2009     

圆柱基体热障涂层制备工艺中的残余应力分析

由于基体和热障涂层各层材料的热膨胀系数不同,在温度变化时各部分变形大小也不同,从而导致涂层内部产生残余应力。本文利用过盈配合模型求解圆柱形基体上热障涂层的残余应力,计算了涂层的厚度、弹性模量和热膨胀系数对残余应力的影响,并从应力角度探讨热障涂层的剥落失效。