Polymers formed from plasma-polymerized methane were employed to modify the surface properties of silicone rubber membrane. Polymers were evaluated based on the energy input parameter W/FM, where W is the discharge power, F is the monomer flow rate, and M is the molecular weight of the monomer. Dealing with the characteristics of plasma polymerization and the deposited polymer film, the effect of pumping rate on deposition rate and the coating thickness, surface energy, and gas permeabilities of methane-plasma-polymer-coated silicone rubber membrane were investigated in three plasma regions. Because more reactive species are expelled at high pumping rates, the monomer-deficient region is reached at lower W/FM in the high pumping rate system than that in the low pumping rate system. The composite parameter W/FM had a strong influence on coating thickness, gas permeability, surface energy, and the polar component of the surface energy but little effect on its dispersion component. Examination of gas permeabilities indicated that coating thickness was another important controlling factor on the properties of plasma polymer.

New reaction products have been generated on polyethylene and polystyrene surfaces using a novel two-step process. The first stage involves exposure to a downstream nitrogen plasma, and the second to either ozone or a corona discharge. It is observed that each of the two-step reactions yields very different reaction products, with an apparent increase in the formation of CO functional groups in the former case and the formation of surface NO₂ groups in the latter case.

The effect of a remote nitrogen plasma on polyethylene and polystyrene was studied. The gas flow rate, the dilution of reactant gas, exposure times, and reactor base pressure were all found to have a large impact on the efficiency of nitrogen incorporation. Optimum conditions caused 18 atom % nitrogen to be incorporated within 20 seconds for polyethylene and 10 seconds for polystyrene. Studying a remote nitrogen plasma treated polyethylene sample over a period of 1 month indicated that except for a drop in the % N on initial exposure to air the concentration of nitrogen on the surface remained steady within the experimental limits. Angle resolved photoelectron spectroscopy indicated that nitrogen is incorporated to a depth below the analysis depth of XPS.

Some results are presented concerning the laser-induced photochemical enhancement of the adhesive bonding strength between polypropylene (PP) and adhesives on a resinous basis. The mechanism of the laser-activated processes is discussed. At some conditions a bonding strength enhancement of more than 5 times has been achieved.

The polypropylene films are pretreated in a nitrogen or ammonia low-pressure plasma in order to improve their adhesive properties towards an in-situ deposited aluminium coating. The treatment conditions are similar to industrial ones and treatment times as short as 23 ms allow a considerable improvement of the adhesion between the polypropylene and the aluminium. The aim of this work is to understand better the mechanisms involved in the adhesive phenomena. Indeed, the modifications created by the plasma (for very short treatment times) are not easily detected. SSIMS has revealed the presence of a thin non-homogeneous film of light-weight hydrocarbons on the non-pretreated polymer. This film is responsible for the non-adhesion of the aluminium coating onto the polymer. Actually when this film is removed by a cleaning process induced by the plasma, the interactions between the aluminium and the polypropylene are strong enough to allow a good adhesion. This explains one of the effects of the plasma and more experiments will be carried out in order to determine the key factor of the phenomenon: the role of the oxygen at the interface on the treated polymer will be investigated as well as the diffusion depth of the treating gas.

XPS and contact angle measurement have been used to study oxygen–plasma-treated polypropylene (PP) surfaces aged at variable temperatures. Surface rearrangement leading to low wettabillity has been observed, without alteration of the surface composition, as determined by XPS. Experimental results have been interpreted in terms of internal rearrangements of a modified layer, <5 nm thick, formed on top of the PP and immiscible with it.

We also modelled the composition of the surface layer and calculated the relative mobility of modified and non-modified polymer chains. On this basis, the experimentally observed behaviour can be interpreted in terms of surface rearrangement driven by a compromise between striving for lower surface tension and maximizing inter-and intramolecular interactions, mainly hydrogen bonds.

The surface composition observed after treatment with plasma, corona, flame or other for enhancing surface tension is then time dependent. For this reason, the procedure used for surface analysis, namely the time allowed for surface equilibration, should be specified in reports.

Several commercial polymers (polyethylene, polyimide, polytetrafluoroethylene, polyvinylchloride and polycarbonate) have been treated by low temperature glow discharge plasmas in various gases, namely NH3, O2, Ar, and CF4. These surface modifications were performed in "pure" microwave (2.45 GHz, "single-mode") or in combined microwave/radio frequency (2.45 GHz/13.56 MHz, "dual-frequency") plasma. Important systematic changes of the surface composition, wettability, and adhesion of thin metal films were observed for different substrate bias values, and for the different gases. The modified surface-chemical structure is correlated with contact angle hysteresis of water drops; this helps to identify which surface characteristics are connected with the wettability heterogeneity and with adhesive bonding properties, and how they are influenced by plasma-surface interactions.

Low-pressure plasma treatment has been introduced for the practical pretreatment of automobile bumpers. The differences between the conventional solvent vapor pretreatment and low-pressure plasma or corona treatment, are shown schematically.

The surface free energy of polyacrylonitrile carbon fibers was investigated by using the Wilhelmy technique. The difference in surface free energy between immersion and emersion was observed for the carbon fiber pyrolyzed at 2500 °C.

In contrast, the hysteresis disappeared with repyrolyzation of the carbon fibers at 3000 °C. Auger electron spectroscopic analysis indicated that the surface of the latter carbon fiber (repyrolyzed at 3000 °C) consisted of the basal planes of graphite. Rough surface topography of the carbon fiber repyrolyzed at 3000 °C, as observed by scanning electron microscope, did not affect the hysteresis. Therefore, the contact angle hysteresis was attributed to the chemical adsorbants on the activation sites of the fiber surfaces, as detected by Auger electron spectroscopy.

In a previous paper it was shown that negative interfacial tensions between predominantly monopolar surfaces (i.e., surfaces with mainly H-acceptor properties) and polar liquids are real phenomena. Such negative interfacial tensions do however decay rapidly. For miscible liquids, the decay of the interface is, in general, so rapid that it practically excludes measurement of interfacial tension. However, if one liquid is present in the form of a gel, and if the other liquid is placed as a drop upon the gel, there is often enough time to measure contact angles. This may be done at various concentrations of the liquid encased in the gel, and an extrapolation made to zero concentration of the gelling agent. With this method we found the existence of negative interfacial tensions at liquid/liquid interfaces.

Two different experimental approaches based on ellipsometry and zeta potential measurements have been employed to determine the dispersion and polar surface free energy components of glass. From ellipsometry the adsorption isotherms of n-octane and water have been determined, yielding values for the film pressures of n-octane and water and the dispersion and polar surface free energy components of glass. Similarly, zeta potentials in water of glass covered with various amounts of n-octane and n-hexanol have been determined. Next, the film pressures of these liquids and surface free energy components of glass were also calculated. Thus determined values are 32 and 80 mJ/m² (from ellipsometry) and 25 and 80 mJ/m² (from zeta potentials) for the dispersion and polar components, respectively. The correspondence between the surface free energies obtained by two completely independent methods gives confidence to the approaches employed.

—The effects of oxygen plasma treatment time, duration of storage, and heat treatment on the surface chemistry of and Cr adhesion to Dupont RC5878 and Kapton polyimides were investigated using X-ray photoelectron spectroscopy (XPS), and contact angle and peel strength measurements. The XPS results indicate that the initial stage of plasma treatment involves oxygen adsorption with insignificant modification of the surface chemistry. After 5 s of plasma treatment the surface chemistry is modified, as suggested by the changes in the carbonyl and partially oxidized carbon functional groups' contributions to the C(1s) line shape. These modifications resulted in an increase in the peel strength and a decrease in the contact angle of water. Over the first month of storage, the intensity of the carbonyl functional group peak decreased, while the contact angle increased and reached a steady-state value of 30° after 20 days of storage. These changes are mainly attributed to moisture absorption. Importantly, the metal adhesion to polyimide remained fairly constant over the storage period. The aged plasma-treated surface experienced loss of moisture when baked at 150°C for less than 5 min. This was followed by an increase of the partially oxidized carbon at the expense of the plasma-induced carbon-oxygen bonds at higher baking temperatures or longer times.

Electret charging methods on the basis of gas discharge in air offer many advantages, including a very simple arrangement, no direct contact to the electret surface, and no restrictions on charging temperature. For discharge in air two arrangements are in use: (1)discharge in a parallel air gap and (2) corona discharge. A comparison of both methods, showing significant similarities, is given.

Starting with investigations of charging in a parallel air gap, the practical knowledge is applied to the more complex corona charging. The characteristics of equilibrum electret voltage and its dependence on applied voltage are measured and interpreted theoretically. The influence of deviations in gap spacing on electret voltage is discussed. Electrical breakdowns of the electret foil affect the results. Therefore the role of breakdown is investigated in more detail.

X-ray photoelectron spectroscopy (XPS) and contact angle methods were used to examine the surfaces of an homologous series of poly(ether urethane) (PEU) samples before and after cleaning treatments. Four PEU films with Shore hardnesses varying from 45 to 75 D were studied as well as two commercially available intravenous catheters of related PEUs. The four as received PEU films have similar surface compositions (~79% C, ~17% O, ~2% N, and ~ 2% Si) although they differ in bulk composition. Critical surface tension (γ_c) values are all similar and high (45-46 dynes/cm). The similarity in the surfaces of the four PEUs, despite the differences in their mechanical properties, demonstrates that surface properties do not necessarily reflect bulk properties. Soap washing and methanol-acetone extraction of the PEU films resulted in surfaces more representative of the bulk compositions of the PEUs. Analysis of the intravenous catheters confirmed that they are lubricated with PDMS, a common practice in the medical device industry. This study documents the value of detailed surface analysis for an enhanced understanding of the surface zone of PEUs. It also illustrates how cleaning protocols can remove labile surface species.

Surface tension data can be used for estimating the solubility of polymers in liquids. By determining the apolar and the polar components of the surface tension of polymers and of solvents, the attractive free energy, δG₁₂₁, of a polymer (1) in a given solvent (2) can be established. By also taking into account the contactable surface area of two polymer molecules, immersed in a liquid, δG₁₂₁ can be expressed in units of kT. Solubility then is favored when -1.5 kT < δG₁₂₁ < 0 for apolar systems, and when -1.5 kT < δG₁₂₁ for polar systems. In polar solvents, hydrogen bonding can often increase δG₁₂₁ from <-1.5 kT to > + 1.5 kT. Positive values are frequently attained and this strongly shifts the behavior from insolubility to solubility. A number of proteins exemplify this behavior.

—ESCA, wettability measurements, SEM, weight-loss determinations, and an ink adhesion test were used to characterize low-molecular-weight oxidized materials (LMWOM) formed during the corona-discharge treatment of polypropylene film. Water-soluble LMWOM is readily formed by scission processes occurring during corona treatment. The presence of water-soluble LMWOM complicates the interpretation of wettability-based measurements of corona effectiveness. Surface roughening on corona-treated polypropylene is caused by the interaction of LMWOM and water in a high-relative-humidity environment. LMWOM does not necessarily form a weak boundary layer that hinders subsequent adhesion of ink to the corona-treated film.

The effects of argon glow discharge and selected organic solvents on the surface wettability of poly(ethylene terephthalate) (PET) and on the wettability decay of glow discharged PET films were studied. Glow discharge in argon (30 W/1 min) drastically reduced the initial water contact angle (CA) measurement of PET from 67.0 to 26.2°. The glow-discharge-induced wetting, however, decayed during the first 7 days and stabilized at 33.1°. Treatments in dimethyl sulfoxide, dimethyl formamide, pyrdine, and water at 80°C caused some improvement in surface wettability as shown by decreases of water CAs in the range of 53–56°. When the solvent and glow discharge treatments were applied consecutively on PET, additive effects on improving surface wettability were observed. The stabilized water CAs of the solvent-and-glow-discharged films ranged from 25.0 to 32.1° depending upon the solvent type. The solvent treatments prior to glow discharge either reduced the extent of CA decay or the time taken to reach stabilization on PET films. Scanning electron microscopic evaluation showed no difference between the solventtreated and the untreated PET surfaces, but a finely etched surface was observed on the glow discharged PET at a 40,000 magnification and above. The distinctly different surface of the DMSO-and-glow-discharged PET indicated that morphological changes on PET surface were induced by the solvent.

Surface modification of poly(tetrafluor oethylene) (PTFE) by NH₃-plasma treatment was investigated by means of contact angle measurement, XPS, and ATR FT/IR spectroscopy. The modified surfaces were adhesively bonded to nitril rubber. The NH₃-plasma irradiation made PTFE surfaces hydrophilic. The contact angle of water on the modified PTFE surface was 16 deg, and the surface energy was 62-63 mJ/m². The NH₃-plasma irradiation improved adhesion between PTFE and nitril rubber using a phenol-type adhesive. The peel strength of the joints reached 8.1 × 10³ N/m. Carbonyl and amido groups were created on PTFE surfaces by the NH₃-plasma irradiation. The mechanism of the improvement of adhesion by the NH₃-plasma irradiation is discussed.

The nature of low-pressure glow-discharge plasma, plasma equipment, and the effect of plasma on materials is reviewed. Examples are given of the improved adhesive bonding of polymers after plasma treatment (2–10 times improvement in lap-shear) and of the surface cleaning and chemical modification that occurs during plasma treatment.

The adhension between aluminum and poly(ethylene-co-vinyltrimethoxysilane) (EVS) and poly(ethylene-co-butylacrylate-co-vinyltrimethoxysilane) (EVSBA), respectively, have been studied. For comparison an ordinary low density polyethylene (LDPE), a poly(ethylene-co-butylacrylate) (EBA), and an ionomer regarded as a bonding polymer were studied as well. The peel strength of laminates obtained by pressing were measured by a T-peel test. The structure of the fracture surfaces were investigated by reflection-IR, ESCA, and SEM. The peel strength of the LDPE and the EBA samples were 100 and 700 N/m, respectively. Although the amount of vinylsilane was low, about 0.2–0.3 mol %, its presence had a pronounced influence on the adhesion: 1800 and 3000 N/m for EVS and EVSBA, respectively. This is even higher than the value observed for the ionomer, 1560 N/m. Although there was a marked difference in surface topology, the SEM and ESCA analysis showed that the fracture was cohesive for both EVS and EVSBA. Immersion in water at 85°C increased the peel strength even more, especially in the case of EVSBA (up to 9000 N/m), in contrast to what is normally observed with aluminum polyethylene laminates. The results suggest that strong and nonhydrolyzable bonds, e.g., covalent bonds, have been formed across the polymer-metal interface for the ethylene copolymers containing vinylsilane.