The effect of Ar, Ar/C2H5OH, O2 and Ar/O2 RF (13.56 MHz) plasma treatments on surface free energy and morphology, optical properties and adhesion of polycarbonate (PC) substrates has been studied. Changes in the surface properties were followed as a function of the plasma treatment time. The polar and dispersion components of the polymer free surface energy were determined on the basis of the theory of Owens, Wendt, Kaelble and Uy. It was found that all RF plasma treatments led to an increase in the polar component of PC, mainly due to an increased hydrogen bonding ability. The increase in surface free energy reached its maximum at short plasma treatment with 3:1 gas mixture of Ar/O2. This treatment also led to pronounced improvement of the adhesion of thin SiO2 films plasma deposited on modified PC substrates, while the treatments with pure oxygen or Ar/ethanol plasma had negative effect on the adhesion.

Poly(tetrafluoroethylene) and a fluoroethylene copolymer were surface treated with a 2.45-GHz microwave plasma to enhance their adhesion to a vinylester thermoset. The plasmas were generated with an inert gas (Ar) and with reactive gases (H₂, O₂, and N₂). The lap-joint shear stress was measured on fluoropolymer samples glued with the vinylester. In general, the stress at failure increased with increasing plasma-energy dose. The H₂ plasma yielded the best adhesion, and X-ray photoelectron spectroscopy revealed that it yielded the highest degree of defluorination of the fluoropolymer surface. The defluorination efficiency declined in the order H₂, Ar, O₂, and N₂. Contact angle measurements and scanning electron microscopy revealed that the surface roughness of the fluoropolymer depended on the rate of achieving the target energy dose. High power led to a smoother surface, probably because of a greater increase in temperature and partial melting. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 838–842, 2005
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.22174

This paper describes theoretical and experimental investigations of the effect of an electrode coating on the onset voltage of a corona on negatively stressed electrodes. Dielectric-coated hemispherically-capped rod-to-plane gaps positioned in air are investigated. The onset voltage is calculated based on the self-recurring single electron avalanche developed in the investigated gap. Accurate calculation of the electric field in the vicinity of a coated rod and its correlation to the field values near a bare rod of the same radius are obtained using the charge simulation method. The calculated field values are utilized in evaluating the onset voltage of the corona. Also, laboratory measurements of the onset voltage on bare and coated electrodes are carried out. The effects of varying the field nonuniformity, the coating thickness and its permittivity on the onset voltage values are investigated. The results show that coating the electrodes with a dielectric material is effective in increasing the onset voltage of the corona on its surface. The calculated onset voltage values for coated and bare electrodes agree satisfactorily with those measured experimentally.

There is currently an interest in techniques to control surface and interfacial properties of polymeric materials, such as wettability, adhesion, biocompatibility, friction, and wear, for different applications and technologies and for the design of novel materials. The desired surface properties range from complete release toward all contacting gaseous, liquid or solid substances to irreversible covalent bonding to other substrates of interest. The macroscopic interfacial phenomena describing these properties are wetting, adhesion, and adsorption. They all share a common basis; they are dependent upon the intermolecular and surface forces and, on the molecular level, upon the chemical and physical details of the molecular structure of the surfaces, especially upon the availability of particular functional groups at the surface. This chapter focuses on the strategies to estimate the surface energetic from wetting and surface tension measurements. The fact that the surface chemistry of polymers might differ substantially from the average bulk chemistry is also caused by the structural features of macromolecules. Therefore, it has become a powerful tool to control the surface energetic of polymers by their chemical bulk structures.

This chapter presents a comprehensive study on the thermodynamics of contact angles on general rough, heterogeneous surfaces. Conventionally, contact is defined as the angle formed between a liquid-vapor interface and a liquid-solid interface at the solid-liquid-vapor three-phase contact line. On an ideal solid surface, which is smooth, homogeneous, isotropic, and non-deformable, the contact angle is expressed by the Young equation. The concept of liquid front simplified the thermodynamic treatments of contact angles on rough, heterogeneous surfaces and thus made it possible to model real surfaces. Receding contact angles are poorly reproducible for hydrophilic surfaces but for extremely hydrophobic surfaces, advancing contact angles might have a poor reproducibility. An impurity might cause poor reproducibility for receding contact angles if it is the component with the smallest intrinsic contact angle, but it can make the advancing contact angle. An impurity might not affect contact angle hysteresis if it is the component with an intermediate intrinsic contact angle.

Atomic force microscopy (AFM), contact-angle measurements, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize biaxially oriented poly(propylene) (PP) films modified by exposure to a corona discharge. Surface analysis was performed on PP films modified at various corona energies to explore the changes in surface topography, wettability, and oxidation state resulting from the corona treatment. Even at low corona energies, water-soluble low-molecular-weight oxidized materials (LMWOM) are formed. These LMWOM products agglomerate into small topographical mounds that are visible in the AFM images. For the detection of LMWOM on corona-treated surfaces, AFM appears to be at least as sensitive as contact-angle measurements or ESCA. A major advantage of AFM relative to the other surface analytical techniques used to confirm the presence of the LMWOM is that no washing of the surface with water is required in conjunction with the AFM analysis.

The surface chemistry and nanotopography of low-density polyethylene (LDPE) were modified by downstream, inductively coupled, radio frequency (rf) Ar plasma without inducing surface damage. The extent of surface modification was controlled by the applied ion energy fluence, determined from the plasma ion density measured with a Langmuir probe. The treated LDPE surfaces were characterized by atomic force microscope (AFM) imaging, contact angle measurements, and X-ray photoelectron spectroscopy (XPS). Analysis of AFM surface images confirmed that topography changes occurred at the nanoscale and that surface damage was insignificant. Contact angle measurements demonstrated an enhancement of the surface hydrophilicity with the increase of the plasma power. XPS results showed surface chemistry changes involving the development of different carbon-oxygen functionalities that increased the surface hydrophilicity. Physical and chemical surface modification was achieved under conditions conducive to high-density inductively coupled rf plasma.

Polytetrafluoroethylene (PTFE) surfaces were treated by oxygen and nitrogen species generated either in a remote (filtered) RF plasma or in an ion gun. In the first case, the majority of the species reaching the surface are neutral molecules, whereas in the second case, ions are the reactive agent. In this paper, we show that ions alone do not lead to a significant grafting of new functions on the PTFE surface. The XPS analysis of the treated surface show identical behaviour with oxygen and nitrogen ion treatment, and the evolution of the C1s peak shape suggest a progressive sputtering, leading to defluorination of the surface. The nitrogen plasma treatment lead to a subsequent grafting that is attributed mostly to the “excited neutrals”, but we suggest here that the ions could play a significant role in the activation process of the surface. The exposure of PTFE to an oxygen plasma lead to chemical etching of the surface, different from the physical sputtering induced by the ion treatment, that lead to a super-hydrophobic behavior of the surface attributed to an increase in the surface roughness.

The synthesis of ozone from oxygen in a cylindrical ozonizer operating under surface discharge conditions with a plasma electrode was studied. The conditions of ozone synthesis were optimized. The dependence of ozone concentration and specific energy consumption on gas pressure in the plasma electrode and on distance between the coils of a corona electrode was determined. The results were compared with data obtained with the use of classical surface barrier discharge.