Ultra-thin Plasma Polymer Films Research Articles

Enhanced corrosion resistance of epoxy-films on ultra-thin SiOx PECVD film coated laser surface melted Al-alloys

The influence of ultra-thin SiOx plasma deposited films on the corrosion resistance of adhesive films on a laser surface melted 7075 aluminium alloy was investigated by means of complementary techniques in comparison to the just laser surface melted state. Laser surface melting (LSM) was performed using a continuous wave mode at a wavelength of 1064 nm. Ultra-thin plasma polymer films were deposited from a mixture of hexamethyldisilane (HMDSO), oxygen, and argon by means of an audio-frequency glow discharge. The surface morphology and surface chemistry compositions were investigated by employing field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), diffuse reflection infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy. The corrosion resistance of plasma polymer coated LSM Al-7075 alloy was studied using linear sweep voltammetry and electrochemical impedance spectroscopy in a chloride-containing electrolyte. The electrochemical studies showed an improved corrosion resistance for plasma film-coated alloys compared to the just laser surface melted state. To study the corresponding surface adhesive properties, the samples were coated with an epoxy amine adhesive. 90°-peel test under humid conditions confirmed the improvement of interfacial wet-adhesion corrosion tests showed a strong improvement of the delamination resistance of adhesives caused by the ultra-thin interfacial SiOx-films.

The deformation response of ultra-thin polymer films on steel sheet in a tensile straining test: the role of slip bands emerging at the polymer/metal interface

Abstract Forming of pre-coated sheet metal becomes of increasing importance in various fields of industrial application. In the recent years, ultra-thin plasma-polymer films have emerged as promising candidates as pre-treatments for steel sheet. Not much, however, is known about the forming behaviour of ultra-thin polymer coatings on ductile substrates, while an extensive literature exists for the reverse case, metal films on polymer, or brittle films on deformable substrates in general. For these cases, advanced models exist, mostly based on the so-called shear lag approximation. The heterogenous, highly localized strain and stress distribution, typical of ductile substrates, as well as out of plane displacements at the interface are disregarded, but cannot be neglected at the high strain levels of interest for elastic polymer films. This paper will focus on the role of slip bands on cracking of ultra-thin polymer films.

Promotion of Adhesion of Green Flame Retardant Coatings onto Polyolefins by Depositing Ultra-Thin Plasma Polymer Films: A Critical Review

Various methods have been used for introducing fire retardant additives into polymers. Deposition of thick fire retardant coatings directly onto polymer substrates is an alternative technique. An important advantage of the coating technique is the preservation of the physical and chemical integrity of the polymer material. Moreover, the fire retardancy of the polymer materials can be achieved following their production. Suitable coating materials are inorganics, intumescent, char-forming, oxygen-diluting, and cooling or radical quenching layers. The most important problem is to achieve sufficient coating thickness to withstand the direct attack of flame and to protect the polymer bulk from pyrolysis, otherwise blistering of coating, caused by emitted pyrolysis gases, is often observed. To avoid blistering of coating, the adhesion between polyolefin substrate and fire retardant coating has to be extraordinarily high. In order to achieve such a high level of adhesion, the polymer surface has to be modified with adhesion-promoting functional groups. The deposition of thin plasma polymers as adhesion-promoting layers with NH2, OH or COOH groups has been the most suited method. These functional groups are able to form covalent bonds and other interactions between the fire-resistant coating and the plasma-modified polyolefin substrate. Additionally, the plasma polymer counteracts the strong mechanical stresses in the laminate on exposure to high temperatures by its flexibility. The thick fire retardant coatings were chosen based on green ecological aspects to avoid flame-initiated emission of toxic or corrosive gases and remains of toxic char.

Ultra-Thin Plasma Polymer Films as a Novel Class of Adhesion Promoters: A Critical Review

Several reaction mechanisms have been proposed for formation of plasma polymers, such as monomer fragmentation followed by poly-recombination into randomly structured and crosslinked films; fragmentation, accompanied by the formation of acetylene or other film-forming intermediates and deposition of polystyrene-like material; plasma-initiation of radical chain-growth polymerization; and ion-molecule reactions, as well as ionic chain-growth polymerization. The bulk structure of plasma polymers was found to be more or less randomly formed, far from that of classic polymers. Nevertheless, the retention of functional groups in the plasma polymer is higher than the retention of monomer structure in repeat units of polymer backbones. Such functional groups bearing plasma polymers were found to be suitable as adhesion promoting layers in polymer composites. These functional groups are essential for covalent bonding to substrate and coating. Additional introduction of aliphatic spacers could flexibilize the interface between plasma polymer covered substrate and coating. Thus, maximum adhesion in composites and laminates was produced. Several examples are given where plasma polymers alone or linked with spacers have been shown to be effective as adhesion promoter.

Correlation of interfacial electrode potential and corrosion resistance of plasma polymer coated galvanized steel. Part 1: Ultra-thin plasma polymer films of varying thickness

Ultra-thin SiO 2-like plasma polymer films were deposited on zinc coated steel. Such films led to a strong inhibition of cathodic and anodic electrochemical reactions and a negative shift in the electrode potential. When the SiO 2-like films are additionally coated with a few micron thick organic film, the resulting interface electrode potential is further shifted cathodically down to −0.8 V SHE as measured by means of a scanning Kelvin probe. This interface potential is about the same as the free corrosion potential of zinc in a chloride containing electrolyte. Accordingly, the interface proved to be extremely resistant to cathodic de-adhesion processes.

Substrate influence on the initial growth phase of plasma-deposited polymer films

In this communication we demonstrate that in the initial stages of deposition of ultrathin plasma polymer films, both the growth rate and the chemical composition of the films are affected by the nature of the substrate which is an important question surprisingly neglected until now.

Comparing the growth of PVD silver nanoparticles on ultra thin fluorocarbon plasmapolymer films and self-assembled fluoroalkyl silane monolayers

Adsorbed silver nanoparticles were prepared by means of electron beam evaporation ofsilver on ultra thin Si-supported heptadecafluoro-1-decene plasma polymer films andself-assembled heptadecafluorodecyl-trimethoxysilane monolayers. The morphology of thesilver nanoparticles, characterized by their size, size distribution, shape and interparticleseparation, was observed to depend on the type, chemical composition and surface energyof the sub-layer as well as the amount of silver deposited. Field emission-scanning electronmicroscopy was used to study the change in the morphology of the silver nanoparticles as afunction of the preparation parameters. The silver nanoparticles on the ultra thin plasmapolymer films demonstrated a much smaller and narrower size distribution due to thecross-linking within the film, which more effectively hinders the penetration of silverthrough the film in comparison to the self-assembled monolayers. Moreover, the opticalproperties of the resulting silver nanoparticles on the ultra thin fluorocarbon plasmapolymers and their correlation to size and size distribution were investigatedby spectroscopic ellipsometry in the wavelength range between 300 and 800 nm.

Negative Thermal Expansion in Ultrathin Plasma Polymerized Films

An intriguing large negative thermal expansion behavior was observed in ultrathin plasma polymer films. The thermal expansion of plasma polymerized films exhibited a profound hysteresis between the heating and cooling cycles. The surprising thermal behavior was explained as a consequence of high residual stresses caused by the “wedging” phenomenon.

Spectroscopic analysis of the interface chemistry of ultra-thin plasma polymer films on iron

The bonding of organosilanes to iron surfaces was analysed on three model samples using FTIR-reflection absorption spectroscopy (IRRAS) for the layer characterisation and ToF-SIMS to characterise specific fragments that are commonly interpreted as the proof for a covalent +Si–O–Me-bonding. On an ultra-thin HMDSO plasma polymer coated specimen, characteristic fragments of a covalent bonding of organosilanes to iron oxide surfaces as discussed by other authors could be reproduced, whereas on the pure iron substrate no such peaks could be observed. On an iron surface dip-coated from a diluted polydimethylsiloxane solution, the discussed characteristic fragments of a covalent bonding could be found. This arises questions on the validity of the common interpretation, since in the case of pure physical adsorption of a non-reactive long-chain siloxane, no such bonds should be detectable. Additionally, ToF-SIMS sputter depth profiles on the HMDSO plasma polymer coated iron surface and of the iron surface covered with polydimethylsiloxane could be shown to behave qualitatively identical.

The deformation response of ultra-thin polymer films on steel sheet in a tensile straining test: the role of slip bands emerging at the polymer/metal interface

Abstract Forming of pre-coated sheet metal becomes of increasing importance in various fields of industrial application. In the recent years, ultra-thin plasma-polymer films have emerged as promising candidates as pre-treatments for steel sheet. Not much, however, is known about the forming behaviour of ultra-thin polymer coatings on ductile substrates, while an extensive literature exists for the reverse case, metal films on polymer, or brittle films on deformable substrates in general. For these cases, advanced models exist, mostly based on the so-called shear lag approximation. The heterogenous, highly localized strain and stress distribution, typical of ductile substrates, as well as out of plane displacements at the interface are disregarded, but cannot be neglected at the high strain levels of interest for elastic polymer films. This paper will focus on the role of slip bands on cracking of ultra-thin polymer films.

Correlation of morphology and barrier properties of thin microwave plasma polymer films on metal substrate

The barrier properties of thin model organosilicon plasma polymers layers on iron are characterised by means of electrochemical impedance spectroscopy (EIS). Tailored thin plasma polymers of controlled morphology and chemical composition were deposited from a microwave discharge. By the analysis of the obtained impedance diagrams, the evolution of the water uptake ϕ, coating resistance and polymer capacitance with immersion time were monitored and the diffusion coefficients of the water through the films were calculated. The impedance data correlated well with the chemical structure and morphology of the plasma polymer films with a thickness of less than 100 nm. The composition of the films were determined by means of infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The morphology of the plasma polymer surface and the interface between the plasma polymer and the metal were characterised using atomic force microscopy (AFM). It could be shown that, at higher pressure, the film roughness increases which is probably due to the adsorption of plasma polymer nanoparticles formed in the plasma bulk and the faster film growth. This leads to voids with a size of a few tens of nanometers at the polymer/metal interface. The film roughness increases from the interface to the outer surface of the film. By lowering the pressure and thereby slowing the deposition rate, the plasma polymers perfectly imitate the substrate topography and lead to an excellent blocking of the metal surface. Moreover, the ratio of siloxane bonds to methyl-silyl groups increases which implies that the crosslink density is higher at lower deposition rate. The EIS data consistently showed higher coating resistance as well as lower interfacial capacitance values and a better stability over time for the film deposited at slower pressure. The diffusion coefficient of water in thin and ultra-thin plasma polymer films could be quantified for the smooth films. The measurements show that the quantitative evaluation of the electrochemical impedance data requires a detailed understanding of the film morphology and chemical composition. In addition, the measured diffusion coefficient of about 1.5×10 −14 cm 2 s −1 shows that plasma polymers can act as corrosion resistant barrier layers at polymer/metal interfaces.

Formability of ultra-thin plasma-polymer films deposited on metal sheet: mesoscopic and nanoscopic aspects of defect formation

Forming of pre-coated metal sheet becomes of increasing importance in various fields of industrial application. For instance, the trend in automotive industry goes for ready coated steel sheet that can be formed and cut without loss of performance. This so called “finish first, fabricate later” concept increases the value of the steel sheet supplied by the steel industry and releases the automotive industry from the burden of the coating process. Consequently, studies on the effect of forming on the performance of corrosion protective coating systems adhering to metals sheet are carried out in order to determine the forming limiting curves for existing coatings [1]. New coating systems are sought in order to improve the formability of coating/metal sheet composites. As a very promising step into this direction, in the recent years ultra-thin plasma-polymer films have emerged as candidates for substituting phosphatation and the environmentally critical chromatation as pre-treatments for steel sheet. These Si-containing plasma polymers provide good corrosion protection properties to steel as well as to zinc-coated steel [2–3].

Corrosion mechanisms in theory and practice

Introduction to Surface Reactions: Electrochemical Basis of Corrosion, D. Landolt Introduction to Surface Reactions: Adsorption from Gas Phase, J. Oudar Surface Effects on Hydrogen Entry into Metals, E. Protopopoff and P. Marcus Anodic Dissolution, M. Keddam Thin Oxide Film Formation on Metals, F.P. Fehlner and M.J. Graham Growth and Stability of Passive Films, B. MacDougall and M.J. Graham Passivity of Austenitic Stainless Steels, C.R. Clayton and I. Olefjord Mechanisms of Pitting Corrosion, H.-H. Strehblow Sulfur-Assisted Corrosion Mechanisms and the Role of Alloyed Elements, P. Marcus Further Insights on the Pitting Corrosion of Stainless Steels, B. Baroux Crevice Corrosion of Metallic Materials, P. Combrade Stress-Corrosion Cracking Mechanisms, R.C. Newman Corrosion Fatigue Mechanisms in Metallic Materials, T. Magnin Corrosion Prevention by Adsorbed Organic Monolayers and Ultrathin Plasma Polymer Films, M. Rohwerder, G. Grundmeier, and M. Stratmann Atmospheric Corrosion, C. Leygraf Microbially Influenced Corrosion, D. Thierry and W. Sand Corrosion in Nuclear Systems: Environmentally Assisted Cracking in LightWater Reactors, F.P. Ford and P.L. Andresen Corrosion of Microelectronic and Magnetic Data-Storage Devices, G.S. Frankel and J.W. Braithwaite Organic Coatings, J.H.W. de Wit, D.H. der Weijde, and G. Ferrari Index

Plasma polymerization. X. A systematic investigation of materials synthesized in inductively coupled plasmas excited in tetrafluoropyridazine

AbstractA detailed investigation was made by ESCA of the gross structural features and chemical composition of ultrathin plasma polymer films prepared from tetrafluoropyridazine. The data reveal evidence of extensive rearrangement that accompanied polymerization and that the C:F and C:N stoichiometries of the polymer films were similar to those of the starting monomer. From an initially high contact angle with water the surfaces became completely wettable with time and this is attributed to surface hydrolysis. A comparison is made between surface and bulk compositions. Brief consideration is also given to sleeve effects.