The effect of CO₂-laser treatment on the wettability of mild steel is presented. In addition, data are presented on the initial joint strengths and durability of joints formed between a single-part epoxide and both mild steel and aluminium. A large increase in stressed durability performance was observed with the laser-treated aluminium compared with degreased-only controls. The laser treatment was shown to efficiently remove the organic contamination from the metallic substrates. Auger analysis showed that the laser interacts more with the mild steel than the aluminium adherends, to produce a relatively thick surface oxide. The changes to the mild steel surface introduced by the CO₂-laser treatment facilitate an durability trials was greater with the laser-treated adherends than with degreased-only controls.

This study focused on the behavior of the paper-polypropylene-paper (PPP) laminate while aging in hot oil in the absence of voltage stress. The results provide an understanding of both the quality of the interfacial bond and the performance of this bond during service. X-ray photoelectron spectroscopy performed on two different peeled laminates suggest that the bond failed primarily adhesively. Weibull statistical analysis of the peel strength data obtained on unaged laminates and those aged in polybutene oil at 90°C for 120 hours showed that the strength loss is consistent with one failure mechanism and the failure rate increases with applied stress. For the aged sample, Weibull analysis results are consistent with the prior loss of peel strength due to the aging. Experiments on the solubility of the oil show that lamination reduces the amount of absorption in comparison to the unlaminated composite. Swelling experiments on the individual components show differential swelling between the paper and polypropylene to be the source of the strength loss. The polypropylene swells, and the paper shrinks. Measurements on the laminate show that both paper and polypropylene shrink, indicating that the paper governs the laminate swelling process. During aging, the differential swelling generates internal stresses on the interface. In addition to yielding the magnitudes of these stresses, finite element analysis also predicts plastic deformation and creeping of the polypropylene as well as tensile stresses between the paper and polypropylene at a free edge. Very likely these processes damage the bond and contribute to the loss of bond strength.

The different methods available in the literature to calculate the surface tension of a solid from contact angle measurements are discussed and compared. The discussion is based on the contact angles of water, glycerol, and diiodomethane measured at 20°C on the surface of a side-chain liquid crystalline polymer. Some discrepancies exist among the results obtained with the different methods, mainly between the values yielded by Neumann's equation and those obtained with approaches that postulate the decomposition of the surface tension into several terms associated with different types of molecular interactions (methods of Owens and Wendt and of Good and van Oss). The physicochemical basis of these various treatments is discussed.

The surface free energy and surface structure of poly(tetrafluoroethylene) (PTFE) film treated with low temperature plasma in O₂, Ar, He, H₂, NH₃, and CH₄ gases are studied. The contact angles of the samples were measured, and the critical surface tension γ_c (Zisman) and γ_c (max) were determined on the basis of the Zisman's plots. Furthermore, the values of nonpolar dispersion force γ^a_s, dipole force γ^b_s, and hydrogen bonding force γ^c_s to the surface tensions for the plasma-treated samples were evaluated by the extended Fowkes equation. Mainly because of the contribution of polar force, the surface free energy and surface wettability of PTFE film which was treated with H₂, He, NH₃, Ar, and CH₄ for a short time increased greatly. Electron spectroscopy for chemical analysis (ESCA) shows that the reason was the decrease of fluorine and the increase of oxygen or nitrogen polar functional group on the surface of PTFE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1733–1739, 1997
https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1097-4628(19970328)63:13%3C1733::AID-APP4%3E3.0.CO;2-H

Silicone polymers exhibit good mechanical properties for a variety of biomedical and industrial applications. For instance, silicone rubber has been used for voice prostheses, urinary catheters, contact lens material, and icing coating materials. However, their inherently high hydrophobicity limits certain applications of this material despite its favorable mechanical properties6. Plasma treatment of silicone polymers may affect their hydrophobicity and therewith their boundability to other materials without affecting the bulk properties. Plasma treatment often involves progressive oxidation of the surface and cross-linking of surface molecular groups which inhibits migration of low molecular weight oligomers to the surface. Various gases have been used to modify silicone polymers by plasma treatment, such as oxygen, helium, ammonia, carbon dioxide, nitrogen and argon. Frequently a thin cross-linked, sometimes water washable, silica-like surface layer was produced by plasma treatment, but there is no consensus about the nature of the chemical groups produced at the outermost surface. The surface hydrophilicity created by plasma treatment is often lost over time. This so-called hydrophobic recovery can be influenced by the storage conditions, whether in air or in liquid, temperature or subsequent adsorption of a surfactant.

Low-pressure plasma-treatments aimed to selectively graft-NH2 groups onto the surface of conventional polymers such as polyethylene, polystyrene and polyethyleneterephtalate are described. The combined use of plasma and surface diagnostics allowed elucidation of the effect of the experimental parameters on the extent of the surface modifications and to understand chemical mechanisms involved in the surface processes. The diagnostic approach is essential for engineering polymer surfaces with a dosed relative density of-NH2 groups, for scale-up and process transfer.

A method of preparing modified surfaces, referred to as soft-landing, is described in which intact polyatomic ions are deposited from the gas phase into a monolayer fluorocarbon surface at room temperature. The ions are trapped in the fluorocarbon matrix for many hours. They are released, intact, upon sputtering at low or high energy or by thermal desorption, and their molecular compositions are confirmed by isotopic labeling and high-resolution mass measurements. The method is demonstrated for various silyl and pyridinium cations. Capture at the surface is favored when the ions bear bulky substituents that facilitate steric trapping in the matrix.

Careful measurements of the surface tension of solid polymers, y_s°, based on the data on contact angles for wetting liquids with various surface tension, y_L°, allows one to establish the functional dependence of y_s° = f(y_L°). This dependence is divided into three zones: one zone, where there is no dependence of y_s° on y_L° and two zones where y_s° changes linearly with y_L°.

It was shown that when polyurethanes designed for use in biopolymer applications were immersed in orienting fluids, significant increases in their non-dispersive surface energies took place. The kinetics of the surface energy response were found to be a function of the immersion medium's acid-base interaction potential. Restructuring from the as-cast state, similar to that reported for two-component polyurethane adhesives, occurs in response to thermodynamic demands and is attributable to a preferential concentration of low energy segments in the surface region. Since shifting surface energies in polyurethanes may pose problems in biological applications, an attempt was made to crosslink the surface of the polymers by the use of cold, microwave plasma discharges with Argon as the treatment gas. Plasma treatments proved to be successful, in that polyurethane surfaces so modified responded much more weakly to changes in the polarity of contact media.

Such polymers are commonly used as release coatings for pressure sensitive adhesive tapes. In this paper the bulk, surface, and interfacial structures of polyvinyl N-alkyl carbamates having either decyl or octadecyl side chains are examined. The bulk structures and thermal transitions were characterized using X-ray scattering and differential scanning calorimetry. Dynamic mechanical thermal analysis was used to investigate thermal transitions and rheology (i.e., segmental mobility) of the polyvinyl N-alkyl carbamates. The surface energies of polyvinyl N-alkyl carbamate coatings were determined using contact angle methods, while X-ray photoelectron spectroscopy and static secondary ion mass spectrometry were employed to characterize the near-surface compositional profiles of the coatings. The peel force provided by the polyvinyl N-alkyl carbamate coatings, as a function of aging time and temperature, was measured for a tape having an acrylic acid containing alkyl acrylate based pressure sensitive adhesive. The changes in peel force with aging time and temperature were related to the ability to maintain a stable interfacial structure between the PSA and polyvinyl N-alkyl carbamate coatings. Changes in the interfacial composition upon aging were characterized by comparing the surface compositions of the PSA and polyvinyl N-alkyl carbamate coatings initially, prior to contact, as well as after aging and peeling them apart. The increase in peel force upon aging can be attributed, in large part, to a restructuring at the PSA/polyvinyl alkyl carbamate interface. Energetically favorable acid-base interactions between the basic urethane and acetate groups in the polyvinyl alkyl carbamates and the acrylic acid groups in the PSA provide a driving force for the restructuring. If the segmental mobility within the polyvinyl alkyl carbamate is sufficient, restructuring can occur, leading to increased concentrations of these groups at the PSA/polyvinyl alkyl carbamate interface, resulting in higher attractive forces and greater adhesion. The propensity for the polyvinyl N-alkyl carbamate coatings to restructure upon contact with a polar medium was also characterized by monitoring the receding contact angle of water, as a function of water contact time and temperature. A good correlation is seen between the ability of the polyvinyl alkyl carbamate coatings to provide a low peel force for the acrylate PSA tape and the ability of the coatings to maintain a high water receding contact angle.

Ar⁺1 ion irradiation on a polycarbonate (PC) surface was carried out in an oxygen environment in order to investigate the effects of surface chemical reaction, surface morphology, and surface energy on wettability of PC. Doses of Ar⁺ ion were changed from 5 × 10¹⁴ to 5 × 10¹⁶ at 1 keV ion beam energy by a broad ion beam source. Contact angle of PC was not reduced much by Ar⁺ ion irradiation without flowing oxygen gas, but decreased significantly as Ar⁺ ion was irradiated with flowing 4 sccm (ml/min) oxygen gas and showed a minimum of 12° to water and 5° to formamide. A newly formed polar group was observed on the modified PC surface by Ar⁺ ion irradiation with flowing oxygen gas, and it increased the PC surface energy. On the basis of x-ray photoelectron spectroscopy analysis, the formed polar group was identified as a hydrophilic CO bond (carbonyl group). In atomic force microscopy (AFM) study, the root mean square of surface roughness was changed from 14 Å to 22–27 Å by Ar⁺ ion irradiation without flowing oxygen gas and 26–30 Å by Ar⁺ ion irradiation with flowing 4 sccm oxygen gas. It was found that wettability of the modified PC surface was not greatly dependent on the surface morphology, but on an amount of hydrophilic group formed on the surface in the ion beam process.

Surfactants — an acronym for surface-active agents — are versatile and ubiquitous chemicals. They are found in industrial areas related to detergents (Hancock 1984; Thayer 1993), pharmaceuticals (Tadros 1984; Attwood and Florence 1983), cosmetics (Ainsworth 1993), paints (Nylen and Sunderland 1965), pesticides (Wada et al. 1983; Tann, Berger and Berger 1992) and oil recovery (Neustalder 1984), to mention a few. Mother Nature used them, long before humans, as major building blocks of biological membranes, taking advantage of the so-called hydrophobic effect (Tanford 1980). This chapter focuses on applications of surfactants in liquid film coating processes, and in particular in coatings involving aqueous solutions, as encountered in the photographic industry.

Wetting is basic to coating. Initially air contacts the solid, and during coating the liquid displaces the air from the moving solid surface so that none is visible in the coated film. Thus, coating is a process of dynamic wetting. For uniform coating, the wetting line must remain straight and advance steadily. At sufficiently high speeds, however, the wetting line becomes segmented and unsteady as a thin air film forms between the solid and liquid. The air film disrupts the uniformity of the coated film, and often air bubbles appear in the coating. Dynamic wetting failure limits coating speed.

Chemical modification of the PET surface by carbon dioxide plasma treatment has been studied using X-ray photoelectron spectroscopy (XPS). The plasma process results mainly in the formation of carbonyl, carboxyl, and carbonate groups at the PET surface. Under rather mild treatment conditions (low plasma power combined with a short treatment time), the formation of CO bonds was found to be dominant, whereas the formation of highly oxidized carbon or double-bonded oxygen-containing groups required a high plasma power or a relatively long treatment time. The treatments performed under excessive conditions frequently led to degradation at the polymer surface. Angle-resolved XPS analyses performed on a freshly modified PET film showed a slight decrease in the O/C atomic ratio when the take-off angle (TOA) increased, indicating a relatively uniform distribution of oxygen within the sampling depth (estimated to be about 8 nm at 80° TOA). The chemical composition of the plasma-modified surface was found to be relatively stable on extended storage in air under ambient conditions. The decrease in oxygen-containing groups at the carbon dioxide-plasma-treated PET surface upon ageing is mainly ascribed to the surface rearrangement of macromolecular segments, the loss of oxygen-containing moieties introduced by the plasma treatment, and the possible migration of non-affected PET chains from the bulk to the surface region.

Surface modification of Kapton polyimide film (325 nm thick) by means of chromic acid and perchloric acid at different times and temperatures has been carried out. The contact angle of water decreased from 82 to 55° and the surface energy increased accordingly from 26 to 45 mJ/m² with times of etching by chromic acid up to 45 min at 33°C. Etching at higher temperatures increased the surface energy. Chromic acid was more effective than perchloric acid. IR and XPS studies indicated multiple bonding and generation of poler groups on the surface. The peak at 1778 cm^-1 due to the imide group decreased on acid etching. The O/C ratio increased and the N/C ratio decreased. The peel strength of the joint polyimide film/copper film/epoxy adhesive/aluminium sheet increased about two-fold on modification of the polyimide (PI) film at 33°C for 45 min, although the changes were marginal for the PI film/silicone rubber/PI film joint. The peel strength is a function of the time and temperature of etching.

In extrusion coating, the inadequate adhesion between the polymer coating and the fiber-based paper substrate (paper and paperboard) is both a common and a constant problem. The lack of adhesion between the printing ink, or glue, and the polymer coating is another area where adhesion improvement is needed. The common means of improving adhesion are flame, corona, and ozone treatments. A modem extrusion coating line is equipped with both a pretreatment and a post-treatment unit. From the work presented here, the following observations were made. The higher the applied corona power and the thicker the coating, the higher the surface energy and polarity of the low density polyethylene (PE-LD) surface. When a high corona power was applied to the coating, only the polar component of the surface energy was increased. The surface energy decreased sharply as a function of aging, but remained more or less constant after about 2 weeks' storage time. The contact angles of water on paper correlated well with the oxygen contents (determined by ESCA) and with the applied corona power. The polarities of both paper and paperboard increased as a function of the applied corona power. Corona pretreatment of paper and paperboard improved their adhesion to PE-LD remarkably. The adhesion of the polypropylene (PP) homopolymer is based more on mechanical interlocking than on interfacial bonding. On the other hand, the oxidizing pretreatments of the paper substrates significantly promoted the adhesion of the PP copolymer.

One of the causes leading to low bond strength between a coating and a substrate (adhesion strength) - if coatings are formed at elevated temperatures in air - is assumed to be a weak boundary layer generated in the region of adhesional contact: the boundary layer consisting mostly of low-molecular-weight products resulting from thermal oxidative degradation of the polymer. It has been verified experimentally that products of oxidation diffuse from the coating surface layer to the contact area. The oxidation process is supposed to be localized within that surface layer. A method has been devised to determine the thickness of the layer, and model experiments have been conducted to show that low-molecular-weight products of oxidation deteriorate the adhesion strength. Ways have been found to increase the adhesion strength of coatings by means of modification of the coating applied in a layer-by-layer manner. The idea is to introduce separately such modifiers as antioxidants, inorganic fillers possessing high adsorption capacities, and crosslinking agents into the coating surface layer. This method of coating modification allows one to eliminate the negative effects of the low-molecular-weight products generated in the surface layers during the formation.

Surface modifications of polyetheretherketone (PEEK) made by chemical etching or oxygen plasma treatment were examined in this study. Chemical etching caused surface topography to become irregular with higher roughness values R_a and R_q. Oxygen plasma treatment also affected surface topography, unveiling the spherulitic structure of PEEK. R_a, R_q and surface area significantly increased after plasma treatment; topographical modifications were, nonetheless, moderate. Wetting angle measurements and surface energy calculations revealed an increase of wettability and surface polarity due to both treatments. XPS measurements showed an increase of surface oxygen concentration after both treatments. An O:C ratio of 3.10 for the plasma-treated PEEK surface and 4.41 for the chemically-etched surface were determined. The results indicate that surface activation by oxygen plasma treatment for subsequent coating processes in supersaturated physiological solutions to manufacture PEEK for biomedical appiications is preferable over the chemical etching treatment.

A theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday. Results are obtained, in concentric sphere geometry, for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions, negative ions and metastable oxygen molecules, coupled with Poisson's equation. A series of ‘saw-toothed’ current pulses of period about is predicted with a DC current level. Accompanying the current peaks are discrete pulses of light 30 ns wide. Successive ‘shells’ of positive ions, from successive current pulses, carry 96% of the mean current. The mean current - voltage relationship has the classic square-law form. The seed electrons required for successive pulses are detached from negative ions by metastable oxygen molecules. Photo-ionization is crucial for the discharge at the anode and for the formation of negative ions throughout the gap. The pulse frequency varies with applied voltage and is found to be approximately proportional to the positive-ion mobility. The surface electric field at the central electrode remains close to Peek's onset field. The origin of onset streamers is explained and sub-microsecond voltage pulses are found to produce streamers. The results for concentric-cylinder electrodes are described briefly.

Injection-moulded plates of ten polypropylene (PP) and thermoplastic polyolefin (TPO) materials with varying material composition (different type of rubber, varying degree of ethylene etc.) were characterized before and after oxygen plasma treatments. Untreated materials were studied by means of differential scanning calorimetry (d.s.c.), size exclusion chromatography (s.e.c.), Fourier-transform infrared spectroscopy (FTi.r.), attenuated total reflectance (ATR) and transmission measurements, and the effect of plasma treatment conditions was followed by X-ray photoelectron spectroscopy (X.p.s.) and contact angle measurements. S.e.c. analysis revealed only minor variations among the materials, while the d.s.c. and FTi.r. experiments confirmed that the differences were to be expected as a result of the variation in material composition. The FTi.r.-ATR results showed that all samples had a gradient in material composition. The materials were generally more rich in PP in the topmost ∼ 200 nm than in the first ∼800 nm, and a lesser extent of ethylene modification and/or rubber was observed in the topmost ∼ 200 nm. It was also shown that the degree of surface crystallinity was normally greater at ∼ 800 nm than at ∼ 200 nm, and that a higher mould temperature led to a higher degree of surface crystallinity. The water contact angles and the atomic composition showed that the materials were more oxidized after plasma treatment at high power-to-gas pressure (P/G) ratios than at low ratios. Moreover, the dependence on material composition was weak for samples that were plasma-treated at low P/G ratios whereas the materials that were least ethylene-modified were less oxidized than the others at high P/G ratios. © 1997 Elsevier Science Ltd.

Polypropylene sheets are treated with oxygen plasma for the interfacial control of GF/PP composites. The interfacial strength between glass fabric and PP resin is estimated by the T-peel test method. The evaluation of T-peel test data is done by both the T-peel strength method and the T-peel amplitude method. The T-peel strength value and T-peel amplitude value were respectively increased to about 50% and 120% compared with each value of non-treated specimens. The T-peel strength relates to the surface energy on the PP-sheet and the T-peel amplitude relates to the fracture pattern of the delamination surface. From SEM observations on the delamination surface, many voids in the space enclosed with fiber bundles are observed in the case of non-treated specimen and no void and fiber bridging are observed on the plasma treated specimens. It is found that interfacial properties between fiber and resin are improved by this plasma process.