Ozlem Ozcan

Silicon oxide barrier films deposited on PET foils in pulsed plasmas: influence of substrate bias on deposition process and film properties

A widely used plastic for packaging, polyethylene terephtalate (PET) offers limited barrier properties against gas permeation. For many applications of PET (from food packaging to micro electronics) improved barrier properties are essential. A silicon oxide barrier coating of PET foils is applied by means of a pulsed microwave driven low-pressure plasma. While the adjustment of the microwave power allows for a control of the ion production during the plasma pulse, a substrate bias controls the energy of ions impinging on the substrate. Detailed analysis of deposited films applying oxygen permeation measurements, x-ray photoelectron spectroscopy and atomic force microscopy are correlated with results from plasma diagnostics describing the deposition process. The influence of a change in process parameters such as gas mixture and substrate bias on the gas temperature, electron density, mean electron energy, ion energy and the atomic oxygen density is studied. An additional substrate bias results in an increase in atomic oxygen density up to a factor of 6, although plasma parameter such as electron density of ne = 3.8 ± 0.8 × 1017 m−3 and electron temperature of kBTe = 1.7 ± 0.1 eV are unmodified. It is shown that atomic oxygen densities measured during deposition process higher than nO = 1.8 × 1021 m−3 yield in barrier films with a barrier improvement factor up to 150. Good barrier films are highly cross-linked and show a smooth morphology.

Water and Ions at Polymer/Metal Interfaces

The adsorption and transport of water and ions at polymer/metal interfaces has a strong impact on the adhesion of the polymer as well as on the kinetics of corrosive degradation. Although not directly correlated both wet-de-adhesion and corrosive de-adhesion are accelerated by water enrichment at the interface which promotes the ingress of ions. The discussion of these phenomena starts with the consideration of the adsorption of water on oxide surfaces, as all engineering metals are covered with an ultra-thin atmospheric oxide film, and ends with the cathodic and anodic corrosive de-adhesion mechanisms of polymers from oxide covered metals. The bridge between the water adsorption and corrosive de-adhesion reactions is built based on the separation of water and ion transport in polymeric interphases and the discussion of diffusion and migration as the principal processes.

Single Molecule Desorption Studies on Immobilized Nanoclay Particle Surfaces

AFM-based single molecule force spectroscopy was performed on sheetlike inorganic particles of Na-montmorillonite to study the pH-dependent adsorption and desorption behavior of polyelectrolytes in aqueous solutions. Polyallylamine macromolecules were covalently attached on gold-coated AFM cantilevers. Heterogeneous surfaces were formed by immobilizing the nanoclay sheets on mica-stripped ultraflat Au(111) surfaces using aminothiol chemistry. Because of the constant surface charge of the particles over a wide pH range, polymer line charge density was the only parameter that affected the adsorption and desorption behavior when the ionic concentration was kept constant. Polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) was performed on cast polyallylamine films to study the pH-dependent charge density of polyallylamine molecules. A good correlation was found between the line charge density and the adsorption characteristics of polyallylamine.

Molecular Studies of Adhesion and De-Adhesion on ZnO Nanorod Film-Covered Metals

This paper aims at the investigation of the effect of ZnO nanorod film deposition on the adhesion between a zinc surface and a model epoxy-based adhesive, with and without the adhesion promoter 3-aminopropylphosphonic acid (APPA) treatment. The stability of octadecylphosphonic acid (ODPA) monolayers on ZnO nanorod surfaces was investigated by means of contact angle measurements and FT-IRRAS to simulate wet de-adhesion conditions at the phosphonate-zinc oxide interface. Peel tests were performed under controlled humidity to study the wet de-adhesion of the model epoxy-amine coating from the ZnO nanorod surface. The deposition of ZnO nanorod films resulted in a significant increase of peel forces in comparison with bare zinc. In the case of APPA-treated ZnO nanorod films the increase of the macroscopic adhesion forces was more pronounced. The high surface area ZnO nanorod films provide for the adsorption of polymers as well as adhesion promoters and makes them promising candidates for improving the adhesion properties of engineering metals.

Physico-Chemical Characterisation of Protective Coatings and Self Healing Processes

The assessment of repair or self healing for advanced materials and novel coating systems can be performed using electrochemical methods or physicochemical methods. In this chapter the authors review the literature both inside and outside the field of self healing materials on a range of characterisation techniques that can be used for determining the level of self healing. Techniques include direct measurement of healing, vibrational, electron and optical spectroscopies, particle techniques and tomographic techniques. Limitations and pitfalls in the use of these techniques for determining the level of healing are also discussed.