ABSTRACTS
The following is a list of the abstracts for papers which will be presented in THIRD INTERNATIONAL SYMPOSIUM ON ADHESION ASPECTS OF POLYMERIC COATINGS. The listing is alphabetical by presenting author. This list is updated continually to add abstracts as they become available and make appropriate corrections. This list may be conveniently searched by using the editor provided with most popular browsers (e.g. Microsoft Explorer, Netscape, ... etc.)
Ultrathin Organic Layers as Adhesion Promoters and Corrosion Inhibitors
The adsorption and self-organisation process of alkyl-phosphonic acids and phosphoric acid monoalkyl esters on technical aluminium surfaces have been investigated by different surface sensible techniques. The aim of these studies was to replace the present technical procedure for pretreatment of aluminum surfaces with chromate acid in order to improve the corrosion inhibition and the coating adhesion.
The ability for self-assembly is given by substances which have a surface reactive group and a long-aliphatic or aromatic spacer and a supramolecular order is built-up between these spacers. The results show that these molecules are able to adsorb spontanously onto the aluminum surface and subsequently a structured molecular order is formed.
Also polymeric nano-particles with phophoric acic groups form a thin smooth well-packed film on aluminium surfaces. Surprisingly we could watch that the film formation process of the functionalized crosslinked microspheres is much faster the smaller the particles.
These effects were confirmed by industrial linked adhesion and corrosion tests.
New results with thiophene functionalized alkyl phosphonic acids and their polymerization with thiophene on the surface will be showed also.
Carbon Fiber-polyaniline Composites: Kinetics of Electrodeposition of Polyaniline Onto Carbon Fibers by Cyclic Voltammetry
Homogeneous and uniform coatings of polyaniline were successfully deposited on carbon fibers by aqueous electropolymerization technique using p-toluene sulfonic acid as the electrolytes. Electrochemical polymerization of aniline was carried out by cyclic voltammetry in the potential range of -0.2V to 1.0V vs. SCE. The electrochemical polymerization parameters such as the number of cycles, scan rate, monomer and electrolyte concentration were systematically varied. Gravimetric analysis showed that the amount of composite coatings on carbon fibers was dependant on the electrochemical deposition parameters. From the weight gain analysis, rate of the reactions were calculated. The effect of surface morphology on the adhesion of carbon fibers onto epoxy was studied in detail.
The Role of Ions Diffusion in the Cathodic Delamination Rate of Organic Coated Steel
A very important mechanism of organic coating deterioration is the cathodic delamination. The basic knowledge about the diffusion mechanism of ions, oxygen and water through the coatings and through the defects in the coatings is not yet sufficient to improve performance of the organic coatings by developing more resistant coatings, and more research is necessary. In this study a new special electrochemical cell has been developed in order to maintain separated the solution in contact with an artificial defect (inner solution) and the solution in contact with the rest of the intact organic coating (outer solution). In this way it is possible to polarize the sample in the cathodic region and to control the environment (ions and concentration, oxygen, water activity) in the defect and around the defect. With this cell many identical samples of polyester coated phosphatised steel were studied. The cathodic delamination was measured, as a function of the different solutions, by measuring the distance of delamination from the artificial defect after different hours of exposure in polarization condition. The experimental results can be discussed as a function of two parameters: the starting time (time necessary to note the beginning of delamination) and the delamination rate (square millimeters of delamination per hour). Comparing many experimental data it is possible to obtain new and interesting information on the delamination mechanism, determining also the rate controlling step of the phenomenon, which is the cation diffusion both through the coating and through the defect. The proposed mechanisms were confirmed also by SEM observation and surface analysis.
6, rue Boussingault 67083 Strasbourg, FRANCE
Distribution of Small Molecules in Waterborne Coatings
Waterborne coatings very often also contain low molecular weight species, intentionally or not. These small molecules can be, for instance, undesirable residual monomers or oligomers; or they can be voluntary added formulation additives like wetting agents, crosslinkers, adhesion promoters, plasticisers, coalescents, stabilisers, texturing agents,…
In all cases, these molecules have a profound influence on properties like adhesion. Not only do the small molecules affect adhesion through their total amount, but also, at a given concentration, through their distribution in the film. A better control of the distribution of small molecules in organic coatings would lead to a marked improvement in properties. Controlling the distribution first requires a better understanding of the complex phenomena leading to the concentration profile of a small molecule in a polymeric film prepared under given conditions. Lots of efforts have been committed in industry and academia in that direction. However, the level of understanding is still not satisfactory because of the complexity of the underlying phenomena and the variety of the systems.
This lecture does not aim to be a general literature review of the problem of distribution. It will mainly give a recent example of what is done in academia in this field. The example deals with the distribution of surfactants in waterborne silicone films. Silicones, used as hydrophobic waterproofing joints or films, adhesives, or coatings for release papers, are under the same pressure of VOC regulations than other organic compound releasing systems. Consequently, efforts are committed to develop waterborne systems, in which surfactant distributions play key roles in influencing adhesion.
Improving Wet Adhesion of Waterborne Acrylic Dispersion on Wood by Bond Activation
(Abstract not yet available)
1) Dept. of Chemical, Biochemical and Materials Engineering, Stevens Institute of Technology, Hoboken, New Jersey 07030
2) Army Research Laboratory, Aberdeen, MD
3) presently with the Mahidol University, Bangkok, Thailand
The Width of The Epoxy-alumina Interphase
At a polymer-solid interface, an inorganic adherend may influence the structure and/or chemistry of the polymer in the near-interface region. This region is referred to as the interphase. While there is general agreement that interphases exist, there is debate concerning the characteristic length scale of the interphase and its composition and structure. The present research examines the size and composition of the epoxy-aluminum interphase using spatially resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Aliphatic PACM20 [bis(p-aminocyclohexyl)methane] curing agent and aromatic DGEBA [diglycidyl ether of bisphenol-A] epoxy resin were selected as a model system. Spatially resolved -*, carbon, and thickness profiles were measured using EELS in the epoxy region immediately adjacent to the interface between the bulk epoxy and the nanoporous oxide on the aluminum adherend surface. These profiles systematically show deviations in the spectral intensities characteristic of carbon and aromaticity over distances extending 90±15 nm from the oxide surface. Simulations of such data indicate that these fluctuations cannot be accounted for by variations in specimen thickness but rather result from changes in epoxy composition near the oxide surface. The results show that this epoxy-aluminum interphase is enriched in curing agent, as indicated by a gradual compositional change from 25±5 vol% PACM20 in the bulk epoxy to 80±15 vol% PACM20 at the epoxy/oxide interface. This chemical segregation has important implications on the properties and performance of epoxy-aluminum adhesive joints. Work is undergoing to study levels of hydration in such systems with a goal of addressing how moisture in interphases affects composite durability.
Surface Adhesion in In-Situ Phosphatizing Coatings
Surface adhesion of an organic coating depends generally on the density and uniform distribution of primary chemical bonds produced between polymer films and metal substrates, and also on the formation of a defect free and highly dense paint film that is impermeable by electrolytes. In this presentation, a "green chemistry" technology of metal finishing, in-situ phosphatizing coatings (ISPCs), will be described. In an ISPC, the in-situ phosphatizing reagent (ISPR) is pre-determined and its optimum amount is pre-dispersed in the paint systems (water-based or solvent-borne) to form a stable and compatible coating formulation. When an ISPC is applied to a bare metal substrate (cold-rolled steel, aluminum alloys - 3003 and 2024 T3, or titanium alloy - Ti-6Al-4V), the phosphatizing reagent chemically and/or physically reacts in-situ with metal surface to produce a metal phosphate layer and simultaneously forms covalent P-O-C (phosphorus-oxygen-carbon) linkages with the polymer film. Both 3 and vibration modes in PO43- for the interfacial metal phosphate layer and band structure at 934 cm-1 for the P-O-C linkage are observed in the grazing angle refractive FTIR spectra. The surface morphology of a smooth, dense, and uniform metal phosphate layer is verified by the SEM/EDX scans.
In an ISPC, the ISPR is designed to provide a dual purpose of generating in-situ metal phosphatization and catalyzing the polymer curing reactions. The paint system catalyzed by ISPR gives a dense and corrosion-resistant film, and a thermal stable and defect free coating. The surface adhesion of ISPCs is characterized by saltwater immersion and cathodic delamination tests. The corrosion inhibition of ISPCs is quantified by salt (fog) spray test and electrochemical impedance spectroscopy. The coating protective performance of ISPCs is shown to be superior to that of the current multi-step coating practice. The technique of ISPC is a one-step self-phosphating process and uses no toxic form of chromium (Cr6+). The recent advancement on the effects of incorporating organofunctional silanes in ISPCs (i.e., 2nd generation ISPCs) will also be discussed.
Influence of Coating and Substrate Properties on the Adhesion of Polymeric Coatings
In this paper it will be argued that the practical adhesion between a substrate and a polymeric coating may be rationalised in terms of the Griffith-Orowan theory of fracture. According to this theory, the strength, fracture stress of a material, sf, is given by
sf = k(EG/l)½
where k is a constant, l is the length of the critical crack which leads to fracture, E is the modulus and G the fracture energy. Fracture will occur where the term EG/l is lowest. When the theory is applied to substrate-coating adhesion, it is necessary to recognise that E and G are semi-local properties, the values of which can be influenced by the properties of both coating and substrate. Thus modification of the properties of one of the phases joined, or of the interface between them, may alter absolute value and the locus of the minimum of EG/l. This will change the practical adhesion, even though fracture may occur remote from the site of the modification.
Examples will be discussed showing how a wide range of levels of adhesion can be obtained between the same substrate and coating. The adhesion depends upon the properties of the substrate-interface-coating system taken as a whole.
Nanoscale Scratching of Polymers
As the thickness of functional coatings continually decreases to satisfy the structural and protective needs of modern day thin film applications, quantitative instrumentation has become a necessity for adequate evaluation of material properties, particularly scratch resistance and plastic deformation of the coating. The Nano-Scratch Tester (NST) is a new instrument overcoming the limitations of both the classical stylus scratch test (normal force range) and the scanning force microscope (SFM) technique (short sliding distances), allowing scratch lengths of up to 10 mm. Tangential force and penetration depth are simultaneously measured during the scratching process, providing important complimentary information in addition to assessment of scratch damage. For high resolution inspection of the deformed or damaged area, a scanning force microscope (SFM) is integrated into the system. Experimental results are presented for a range of polymer materials where the pre- and post-scan modes of scratching allow the true penetration depth to be measured as well as the residual depth after scratching. The latter provides information about the viscoelastic properties of the material and correlates well to other test methods (e.g. mar resistance, gloss retention, etc.).
1) Maharajas College, Ernakulam, INDIA-682 011
Optical and Thermal Characterization of Plasma Polymerized Diethylaniline Thin Film
Material synthesizing, processing and characterization is one of the most active areas of research in the development of science and technology. Plasma polymerization has been widely used for the preparation of materials from a large variety of compounds. Plasma polymerised thin films are highly adhesive and are extensively used in the corrosion resistant applications. From microelectronics to sensor technology, these films find applications in most of the relevant fields of the present century. Although the optical and dielectric properties of various plasma polymerized films are reported from time to time, the thermal properties remain unexplored to a certain extent. In the present work, in addition to the optical properties, the thermal diffusivity of r.f. plasma polymerized diethylaniline thin film is reported. The optical properties like direct band gap energy, indirect band gap energy and refractive index of the thin film is determined from UV-Vis-NIR absorption and transmission spectra. The possible linkage of polymerization is suggested from the FTIR spectra, though the exact structure of the polymer cannot be predicted due to the cross-linked and highly branched nature of the plasma polymers. The thermal diffusivity of the poly diethylaniline thin film is determined using the Probe Beam Deflection (PBD) technique, one of the most sensitive of photothermal techniques. Various other photothermal techniques like photoacoustics, pyroelectric techniques can also be used for material characterization. However, our sample being thermally thin and optically transparent, it is difficult to employ the latter two techniques for successful evaluation of thermal diffusivity. The probe beam deflection signal is analyzed using the Phase method for the determination of thermal diffusivity.
Failure of Bulk and Thin Film Glassy Polymer Adhesives
We present recent results from molecular level modeling of elasto-plastic deformation, and craze formation and breakdown in glassy polymer adhesives. Linear chain molecules are modeled through a coarse-grained bead-spring model, which is studied with molecular dynamics (MD) simulations. Small elemental volumes are considered that represent different stages of failure in bulk polymers or polymer coatings. We first consider small strains and compare the yield behavior of the model polymer to established shear yield criteria for general loading conditions. When the stress is sufficiently tensile, the polymer fails by cavitation and crazes develop at large strains. As the craze widens, the dense polymer is expanded into a fibril network. Our simulations reproduce experimental trends with temperature and strain rate. In the final stage, the craze fibrils fail either through chain pullout or chain scission. The onset of chain scission and the fibril breaking stresses are calculated as a function of chain length and entanglement density. We conclude with a multiscale calculation of the macroscopic toughness of glassy polymers, in which we combine MD results from the microscopic volumes with a continuum fracture model.
Evaluation of Adhesion property of Conducting Polymer Composite Coatings on Al-2024
Substitute Polyaniline composite coatings were electrodeposited onto Al-2024 in aqueous solution of oxalic acid. The coatings were electrodeposited using both cyclic voltammetry and galvanostatic polymerization. Filler like carbon fibers and carbon black have been used to make the composite coatings. The adhesion properties of these coatings are evaluated using Dynamic Contact Angle Analyzer (CAHN instruments). The effects of various electrodeposition parameters like monomer concentration, filler concentration, deposition time and the applied current density onto the adhesion property of the coatings have been studied.
Peelable Seals with Polymer Coated Packaging Steels
Polymer coated packaging steels are new products that offer new developments in steel packaging. The polymer coatings offer excellent protection of the packed food, make lacquering superfluous and are ideally suited for difficult products. Next to that, the polymer coatings of the packagings steels can be used to form joints by sealing.
Modern packages should be safe and easy-to-open for consumers. Conventionally, easy openable steel lids can be achieved by scoring. An improvement to this, are closures achieved by sealing of the polymer coating with lid materials with a peelable polymer layer.
A review is given on the factors that determine the peelability of the sealed polymer coatings. The technologies used to produce peelable polymer coatings are discussed. Peelability is however only one important functional property of closures of steel based packages. Peelable seals must also withstand pressure differences at elevated temperatures in moist atmoshpere during pasteurisation or sterilisation of filled packages. The potential of polymer coated packaging steels together with peelable seals for improvements and new developments will be discussed.
Characterizing Polymer Viscoelasticity Using Nanoindentation
For many industry-relevant polymer systems, including polymeric coatings, early times-to-failure can be linked to local chemical and physical degradation, including local changes in mechanical behavior. Further, the interphase regions that form at the component interfaces of coating systems affect performance attributes such as adhesion. Development of techniques to characterize microscale and nanoscale mechanical properties thus is important for understanding degradation mechanisms and improving the durability of these materials. In this presentation, nanomechanical measurements of several polymer systems are discussed, including the characterization of viscoelastic behavior.