Structure and properties of nanosized coatings deposited onto polymers

Results of studies aimed at developing a new approach to measuring stress-strain properties of nanosized solids (strength, yield stress, and the value of plastic deformation at uniaxial tension) are generalized. This approach is based on the analysis of the parameters of microrelief arising upon the deformation of polymer films with thin coatings. It is demonstrated for the first time that the stress-strain properties of aluminum coatings deposited onto Lavsan substrates depend on the level of stresses in the substrate, the value of its deformation, and the thickness of the coating. The evolution of these parameters is related to the strain hardening of metal and the effect of nanostructuring of crystalline materials in the range of small thicknesses. When precious metal (Au, Pt) nanosized films are deposited onto polymers by ion-plasma sputtering, in the course of metal deposition, polymer surface layers interact with cold plasma. Stress-strain properties of polymer surface layers modified by plasma are quantitatively estimated for the first time. The model is proposed that makes it possible to take into account the contribution of the properties of precious metal and plasma-modified polymer surface layer to the strength of the coating.     

Structural aspects of the deposition of metal coatings on polymer films

An electron-microscopic study of the formation of thin metal coatings (gold and aluminum) on a PET film is performed. During the deposition of gold coatings, a well-pronounced interfacial polymer/metal layer is formed, while, in the case of aluminum coatings, the polymer/metal interface is well-defined. The assumption is made that this effect is caused by different chemical activities of metals deposited on the polymer.     

Correlation between structure and stress-strain characteristics of metallic coatings deposited onto a polymer by the method of ionic plasma sputtering

Data on the strength of coatings based on noble metals (Pt, Au) deposited onto PET films by the method of ionic plasma sputtering are analyzed. In addition to precipitation of the metal, this mode of deposition is accompanied by modification of the surface polymer layer due to its interaction with plasma. As a result, a complex three-layered structure near the polymer surface forms. A new method for estimating the strength of coatings deposited onto polymer supports is advanced. This method makes it possible to analyze stress-strain characteristics of the three-layered systems that emerge owing to deposition of nanoscale layers of noble metals on polymer films via ionic plasma sputtering. The proposed relationships are in fair agreement with the experimental data.     

Protective coatings for stainless steel for SOFC applications

In this paper, a coating procedure based on spin coating of metal oxide polymer precursors on stainless steel, which decreases the oxide scale growth rate, is evaluated. The yttrium and cobalt solutions were used as polymer precursors, while a ferritic stainless steel Crofer 22 APU was used for the deposition of protective coatings. The thickness of deposited protective film was about ~500 nm. The effectiveness of protective layer was evaluated by cyclic thermogravimetry, oxide scale electrical conductivity, and X-ray diffractometry. The results show that steel coated with yttrium polymer precursor has better properties than uncoated or cobalt-coated sample.     

The structure and properties of polymer-metallic coating interphase

The structure of the surface layer in polymers (LDPE and PET) decorated with a thin metal (gold and platinum) layer was studied after their deformation under different conditions. It was found that relatively thick coatings debonded from the polymer substrate during tensile drawing. Debonding was observed at low tensile strains (below 20–30%). During the further drawing of a polymer, a regular microrelief typical of deformable “rigid coating on a soft substrate” systems appeared on its surface. This phenomenon is explained by the fact that the debonding metal coating uncovers not the surface of the pure polymer but a certain modified layer, which has a higher elastic modulus than the pure polymer. The formation of this layer is associated with the inclusion of metal atoms into the polymer during the metal decoration by plasma immersion ion deposition. As a result of this inclusion, a modified layer, which has a higher glass transition temperature, a higher elastic modulus, and other mechanical properties, is formed between the coating and the polymer.     

Evaluation of the stress-strain properties of surface layers in plasma-treated polymers

The surface treatment of poly(ethylene terephthalate) (PET) and poly(vinyl chloride) (PVC) films in cold plasma over 1–15 min was carried out. It was found that the subsequent deformation of the films is accompanied by a special type of surface structuring that has been previously observed for polymer films with a thin hard coating. It was shown that unlike metal coatings, the thickness of the modified surface layer slightly depends on the time of treatment in plasma. The previously developed approach to analysis of the emerging patterns makes it possible to evaluate the stress-strain properties of the coatings. It was first revealed that the tensile strength of the modified layer produced in PET by plasma treatment is ∼12.3 MPa and its elongation at break varies from 20 to 90%. The differences in the properties between the plasma-modified surface layers of the polymer and the metal coatings studied earlier are discussed.     

New approach to evaluation of the stress-strain properties of nanolayers of solid materials

The review focuses on results obtained in the development of a new approach to determination of the stress-strain properties (tensile strength, yield point, plastic deformation under uniaxial stretching) of nanolayers of solid materials. The approach is based on analysis of parameters of the microrelief generated by strains in polymer films with hard thin coatings. A significant increase in the tensile strength and ductility of noble metal coatings under uniaxial stretching at the metal layer thickness less than 30 nm is demonstrated for the first time. This substantiates the assumption of a specific state of nanolayers of solid materials. The developed method also enables evaluation of the effect of characteristic defects in solids on their stress-strain behavior. It was found that the stress-strain properties of nanocoatings depend on the physical state of the polymer substrate. A possible mechanism of the revealed phenomena is suggested.     

Mechanism of fracture of metallic coating during uniaxial stretching of substrate polymer at temperatures below its glass transition temperature

The mechanism of fracture is studied for a thin metallic (platinum, gold) coating deposited onto the surface of glassy poly(ethylene terephthalate) that is subjected to uniaxial stretching. The structure of the surface layer in the deformed polymer and the size distribution of the fragments produced by fracture are analyzed. Fragmentation of the coating is shown to take place in a narrow region between the undeformed polymer and the forming neck. Examination of this region allows one to distinguish two different stages of fracture. At the initial stage, the deposited coating randomly breaks down into fairly large fragments. In the region of main orientational transformation of the polymer (in the zone of the forming neck), the predominant mechanism of fracture in the coating is breaking of large fragments formed at the first stage into two equal parts. This mechanism of fragmentation is shown to be universal and independent of the nature of the metal.     

Electrophoretic Deposition of Hydroxyapatite Coatings on Metal Substrates: A Nanoparticulate Dual-Coating Approach

Hydroxyapatite coatings can be readily deposited on metal substrates by electrophoretic deposition. However, subsequent sintering is highly problematic owing to the fact that temperatures in excess of 1100°C are required for commercial hydroxyapatite powders to achieve high density. Such temperatures damage the metal and induce metal-catalysed decomposition of the hydroxyapatite. Furthermore, the firing shrinkage of the hydroxyapatite coating on a constraining metal substrate leads to severe cracking. The present study has overcome these problems using a novel approach: the use of aged nanoparticulate hydroxyapatite sols (lower sintering temperature) and a dual coating strategy that overcomes the cracking problem. Dual layers of uncalcined hydroxyapatite (HAp) powder were electrophoretically coated on Ti, Ti6Al4V and 316L stainless steel metal substrates, sintered at 875–1000°C, and characterised by SEM and XRD, and interfacial shear strength measurement. Dual coatings on stainless steel had an average high bond strength (about 23 MPa), and dual coatings on titanium and titanium alloy had moderate strengths (about 14 and 11 MPa, respectively), in comparison with the measured shear strength of bone (35 MPa). SEM and XRD demonstrated that the second layer blended seamlessly with the first and filled the cracks in the first. The superior result on stainless steel is attributed to a more appropriate thermal expansion match with hydroxyapatite, the thinner oxide layer, or a combination of these factors.     

Specifics of change in the surface area of amorphous poly(vinyl chloride) during its inelastic deformation

A direct microscopic observation procedure was used to study the processes of deformation and shrinkage of poly(vinyl chloride) above its glass transition temperature. Prior to stretching or contraction of the polymer, its surface was decorated with a thin (10–15 nm) metal layer. As a result of subsequent deformation (shrinkage), the decoration underwent structural rearrangements, which were detected by means of direct microscopic examination. These rearrangements contain information on the mechanism of deformation of the polymer substrate. In particular, the procedure makes it possible to characterize the process of development of the interface in the polymer during deformation and the reverse process of interface contraction during the shrinkage of the material. It was found that, in the case of an increase in the interfacial area, its growth is accompanied by a growth in imperfection of the polymer surface layer. These defects can concentrate mechanical stress, thus strongly affecting the fragmentation of the metal decoration on the polymer surface. It was shown that the surface defects could be eliminated by annealing of the polymer above its glass transition temperature. The introduction of a plasticizer that decreases the glass transition temperature below the deformation temperature likewise prevents the development of these defects during an increase in the surface area of the polymer in the process of its inelastic deformation.     

Adhesion of silicon oxide layers on poly(ethylene terephthalate). I: Effect of substrate properties on coating's fragmentation process

Fragmentation tests in the uniaxial mode were performed on poly(ethylene terephthalate) (PET) films coated with a 100 nm thin silicon oxide layer. The coating's fragmentation process was analyzed in light of the mechanical behavior of the polymer substrate. It was shown that, upon unloading samples strained to less than 4% nominal strain, strain recovery leads to the closure of coating cracks. The usual fragmentation diagram, which shows the crack density (CD) versus applied strain, was used to identify the various energy dissipation mechanisms controlling the fragmentation process. An alternative presentation of CD versus true stress provided accurate measurements of both fragmentation and saturation onsets. The interfacial strength was modeled from the CD at saturation according to the Kelly-Tyson approach, including a Weibull distribution of the coating strength. The prediction was compared to the substrate shear stress at saturation. Effects of substrate yield, temperature, and molecular orientation are discussed. It was shown that the coating deposition by evaporation on the PET substrate did not induce structural changes at the polymer interface, whereas heat treatments increased the polymer crystallinity in the interfacial zone, resulting in higher interfacial strength. © 1997 John Wiley & Sons, Inc. J. Polym Sci B: Polym Phys 35 : 1449–1461, 1997     

热诱导金属/聚合物膜系图案化控制的研究

近年来 ,在简单体系上形成复杂规则的图案已引起诸多学者的注意 ,其中以聚合物为母体的体系发展了模板、局部紫外照射和激光诱导等一系列技术 ,从而得到可控的表面图案[1～ 6] .本文用激光刻蚀法对溅射在聚合物膜上的金属薄膜进行处理 ,在热诱导情况下使金属 /聚合物膜系表面产生了规则的图案 .薄膜热应力的可控释放作用和激光刻蚀造成的区域局限作用被认为是诱导这种可控图案产生的两种基本要素 .通过控制激光刻蚀区域 ,可控制薄膜表面形貌变化 ,从而实现可控的图案化设计 .1　实验部分1.1　原料及仪器　聚苯乙烯 (PS) :北京燕山石油化工…     

Transient Behavior of the Metal Interface in Lithium Metal–Garnet Batteries

The interface between solid electrolytes and Li metal is a primary issue for solid‐state batteries. Introducing a metal interlayer to conformally coat solid electrolytes can improve the interface wettability of Li metal and reduce the interfacial resistance, but the mechanism of the metal interlayer is unknown. In this work, we used magnesium (Mg) as a model to investigate the effect of a metal coating on the interfacial resistance of a solid electrolyte and Li metal anode. The Li–Mg alloy has low overpotential, leading to a lower interfacial resistance. Our motivation is to understand how the metal interlayer behaves at the interface to promote increased Li‐metal wettability of the solid electrolyte surface and reduce interfacial resistance. Surprisingly, we found that the metal coating dissolved in the molten piece of Li and diffused into the bulk Li metal, leading to a small and stable interfacial resistance between the garnet solid electrolyte and the Li metal. We also found that the interfacial resistance did not change with increase in the thickness of the metal coating (5, 10, and 100 nm), due to the transient behavior of the metal interface layer.     

Sol–gel titania coating on unmodified and surface-modified polyimide films

Sol–gel coating of metal oxides on polymer substrates is a useful process to fabricate various organic–inorganic hybrid materials under mild conditions. However, this process is hardly applicable to pristine polyimide (PI) films because their surfaces do not display effective functional groups for metal oxide coatings. In this study, we firstly examined direct sol–gel coating of titania thin layers on unmodified PI film surfaces. The results confirmed homogeneous, ultrathin titania layer coating and showed that the thickness and microscopic morphology of the titania layers were affected by titanium alkoxide concentrations in the spin coating solutions. We next investigated titania layer coating on surface-modified PI films that prepared using alkaline hydrolysis, which generated carboxylic acid groups on the film surfaces. Optimal hydrolysis time was determined using FT-IR spectroscopy and contact angle measurements. After sol–gel titania coating on the hydrolyzed PI film surfaces, the Scotch tape test was conducted to evaluate adhesion strength between the titania layers and PI film surfaces. Morphological observations of the sample surfaces after the tests clearly showed that surface modification of PI films increased titania layer adhesions. Effect of hydrothermal treatments on film formability and adhesion strength between titania-PI film interfaces was also evaluated.     

Enhancement of composite‐metal interfacial adhesion strength by dendrimer

The interface between carbon fiber reinforced polymer composites and metal plays a critical role in determining the strength of epoxy/metal laminated composites. We propose to introduce one dendrimer layer into the epoxy/metal interface, aiming to enhance the interfacial adhesion strength so that the interface could more effectively transfer the load from epoxy to metal. In this paper, the preparation and adsorption of dendrimer layer onto the alumina surface were systematically investigated. The results show that a highly stable and nanopatterned dendrimers layer was dip‐coated onto alumina substrates by adsorbing poly (amidoamine) dendrimers. It was confirmed that the dendrimers were adsorbed onto the alumina via acid‐base chemical interactions. The adsorption depends on the reaction time. The adhesion property between dendrimers and alumina was examined by sonication method. Copyright © 2010 John Wiley & Sons, Ltd.     

Solvent-induced porosity in ultrathin amine plasma polymer coatings

Plasma polymers deposited from n-heptylamine onto silicon wafers have been found to form a porous microstructure when immersed in water and other solvents, with pores of dimensions and densities that vary considerably between coatings deposited under different plasma conditions. This solvent-induced pore formation was found to correlate with the observed percentage of extractable material. With low radio frequency (rf) power inputs, the resultant softer coatings possess considerably more extractable material than coatings deposited at higher applied power levels. The porosity is thus proposed to result from the formation of voids created by the extraction of soluble low-molecular-weight polymeric material, which produces shrinkage stress that the coating, firmly attached to the substrate, cannot relieve by macroscopic contraction. The microscopic contraction of plasma polymer volume creates voids that appear to span the entire film thickness. The effect of aging plasma polymers in air was also investigated. For films deposited at low power it led to reduced extraction of soluble material and different pore morphology, whereas for films deposited at higher rf power levels, the extracted amounts and pore formation were the same for aged coatings. It was also found that the density of surface amine groups was lower for films deposited under the two lowest power settings, in contrast to the commonly held belief that the use of minimal applied rf power aids retention of functional groups. These porous plasma polymer coatings with surface groups suitable for further interfacial chemical immobilization reactions may be useful for various membrane and biotechnology applications.     

高长径比管式反应器内壁SiO2与TiO2钝化层的原子层沉积制备及抗积碳性能

采用原子层沉积技术(ALD)在不锈钢微通道管式反应器内壁沉积二氧化硅(SiO₂)和二氧化钛(TiO₂)薄膜, 以抑制碳氢燃料热裂解过程中由于金属催化作用导致的结焦. 使用石英晶体微天平(QCM)测得SiO₂和TiO₂薄膜的生长速率分别为0.15 nm/周期和0.11 nm/周期, 因此可以通过改变沉积周期数精确控制钝化层的厚度. 在结焦实验中, 当钝化膜层较薄时, 其抗积碳钝化作用较弱; 随着钝化薄膜厚度的增加, 其钝化作用逐渐增强, 微通道反应器的运行寿命显著延长. 实验表明, TiO₂薄膜的抗积碳钝化性能普遍优于SiO₂薄膜. 沉积周期数为1000的TiO₂膜层具有最佳的抗积碳钝化效果, 能够使反应器的运行时间延长4~5倍.     

Ultrafine grain formation and coating mechanism arising from a blast coating process: A transmission electron microscopy analysis

This article examines the substrate/coating interface of a coating deposited onto mild steel and stainless steel substrates using an ambient temperature blast coating technique known as CoBlast. The process uses a coincident stream of an abrasive blast medium and coating medium particles to modify the substrate surface. The hypothesis for the high bond strength is that the abrasive medium roughens the surface while simultaneously disrupting the passivating oxide layer of the substrate, thereby exposing the reactive metal that then reacts with the coating medium. The aim of this study is to provide greater insight into the coating/substrate bonding mechanism by analysing the interface between a hydroxyapatite coating on both mild and stainless steel substrates. The coating adhesion was measured via a tensile test, and bond strengths of approximately 45 MPa were measured. The substrate/coating interface was examined using transmission electron microscopy and selected area diffraction. The analysis of the substrate/coating interface revealed the presence of ultrafine grains in both the coating and substrate at interface associated with deformation at the interface caused by particle impaction during deposition. The chemical reactivity resulting from the creation of these ultrafine grains is proposed to explain the high adhesive strength of CoBlast coatings.     

Ion-exchange voltammetry with nafion/poly(sodium 4-styrenesulfonate) mixed coatings on mercury film electrodes: characterization studies and application to the determination of trace metals

This work aimed to produce improved polymer coatings for the modification of thin mercury film electrodes (TMFEs). The goal is to obtain sensitive, reproducible, mechanically stable and antifouling devices suitable for the determination of trace metal cations in complex media. Therefore, novel mixed coatings of two sulfonated cation-exchange polymers of dissimilar characteristics-Nafion (NA) and poly(sodium 4-styrenesulfonate) (PSS)-were produced by solvent evaporation onto glassy carbon electrodes. The effect of the mass ratio (NA:PSS) on the film morphology was studied by scanning electron microscopy, revealing the formation of biphasic polymer systems, where PSS bead-shaped clusters appeared randomly dispersed into a uniform and compact NA environment. The permselectivity/ion-exchange features of the mixed films onto glassy carbon were evaluated using cathecol, urate, and dopamine. To allow trace metal analysis, thin mercury films were plated through the NA/PSS coatings, being the reproducibility and ion-exchange features of the mixed coatings-TMFE evaluated using lead ions. The best NA/PSS coating was found for the mass ratio of 5.3. Analytical performance of the NA/PSS-TMFE yielded a detection limit of 5.5 nM (3sigma), and the application of this modified electrode to an untreated polluted estuarine water sample produced significant improvements in the quality of the signal compared with that for a bare TMFE.     

TiO_2/316L不锈钢薄膜电极在NaCl溶液中的耐腐蚀性能

应用sol gel法和提拉技术于 316L不锈钢表面构筑纳米TiO2薄膜,再经水热后处理以消除膜中的细小龟裂.SEM和XRD技术表征膜的形貌和厚度,线性极化法分别考察膜厚度、pH、和Cl浓度对纳米膜电极耐腐蚀性能影响.电化学交流阻抗检测纳米TiO2膜在 0. 5mol/LNaCl溶液中的阻抗随浸泡时间的变化,光电子能谱技术测定了经浸泡 1008h后的纳米膜中各元素相对百分含量和价态.结果表明:在中性或碱性条件下,厚度为 375~464nm的纳米膜其耐腐蚀性随浸泡时间的延长呈现初期增加而后稳定,浸泡 48h后腐蚀电流较之浸泡初期降低 2个数量级,耐腐蚀电阻增加 2个数量级,在浸泡 1 008h内没有发现腐蚀的产物,Fe是以原子态扩散到膜中.