The effect of oxygen and ammonia plasma treatments on changes of the surface properties of linear high-density polyethylene (HDPE) was studied. Surface energies of the polymer substrates were evaluated by contact angle measurements using Lifshitz-van der Waals acid-base approach. The surface energy of untreated HDPE is mainly contributed by Lifshitz-van der Waals interactions. After 5 min of plasma treatment, hydrogen bonds are formed on the surface, which is reflected in predominant acid-base interactions. The SEM results obtained demonstrate considerable changes of the surface roughness due to different types of the plasma gas used. Evolution of oxygen- or amino-containing moieties was detected by XPS and ATR FT IR. The prepared polyethylene surfaces were used as a basic support for further fabrication of novel hybrid biocomposite sandwich structures.

Surface free energies have been calculated for solid fluorocarbon materials by employing a method that utilizes dielectric data and theoretical predictions of van der Waals (dispersion) interactions. Excellent agreement between the results of direct force measurements and those of the theory for retarded van der Waals interactions supports the methodology. Two relatively new fluorocarbon polymers have been identified as having the lowest known surface free energies of all bulk homogeneous polymeric solids. This study provides confirmation that estimates of solid surface free energies based on contact angle measurements with dispersive organic liquids depend on the dielectric properties of both the liquids and the solid.

Parallel plates dielectric barrier discharge (DBD) at atmospheric pressure has been investigated to modify and functionalize the surface of different polymer substrates, e.g. polyolefins, poly(ethylene terephtalate), polyamide, in order to enhance their hydrophilic properties. Surface properties have been altered to meet the requirements of specific applications by introducing the appropriate functionalities through the use of either acetic acid or ethyl acetate. The coatings have been characterized through wettability measurements, labeling coupled with X-Ray photoelectron spectroscopy, and IR spectroscopy.

Recent progress in the correlation of contact angles with solid surface tensions are summarized. The measurements of meaningful contact angles in terms of surface energetics are also discussed. It is shown that the apparent controversy with respect to measurement and interpretation of contact angles are due to the fact that some (or all) of the assumptions made in all energetic approaches [7–14] are violated when contact angles are measured and processed. For a large number of polar and non-polar liquids on different solid surfaces, the values of γ_1v cos θ are shown to depend only on γ_1v and γ_sv when the appropriate experimental techniques and procedures are used. An equation which follows these experimental patterns and which allows the determination of solid surface tensions from contact angles is discussed.

This chapter discusses the physico-chemical hydrodynamics of rising bubble. At small Reynolds numbers effective approximate analytical methods allow to characterize different states of dynamic adsorption layers quantitatively: weak retardation of the motion of bubble surfaces, almost complete retardation of bubble surface motion, transient state at a bubble surface between an almost completely retarded and an almost completely free bubble surface. The measurement of bubble terminal velocity in water cannot be used for the experimental verification of these theories because uncontrolled impurities in water immobilize a small bubble surface almost completely without any addition of surfactant. The rising bubble velocity relaxation caused by the dynamic adsorption layer (DAL) formation can be measured. The DAL study is more realistic for large bubbles and large Reynolds numbers (Re) because trace concentrations of surface active impurities cannot retard the bubble surface movement completely.

The thin-layer wicking technique was used to determine the surface free energy components and the surface character of three celluloses (Sigmaccll 101, Sigmacell 20, and Avicel 101), using an appropriate form of the Washburn equation. For this purpose, the penetration rates of probe liquids into thin porous layers of the celluloses deposited onto horizontal glass plates were measured. It was found that the wicking was a reproducible process and that the thin-layer wicking technique could be used for the determination of the celluloses' surface free energy components. The size of the cellulose particles was characterized with the Galai CIS-100 system and their crystallinity was measured by X-ray diffraction. The three celluloses have high apolar (y^LWS = 50-56 mJ/m²) and electron donor (γs = 42-45 mJ/m²) components, while the electron acceptor component (γS⁺ ) is practically zero. The free energy interactions of cellulose/water/cellulose calculated from the components are positive, regardless of the cellulose crystallinity. This would mean that the cellulose surfaces have a hydrophilic character. However, the work of spreading of water has a small negative value (3-9 mJ/m²), indicating that the surfaces are slightly hydrophobic. It is believed that the work of spreading characterizes better the hydrophobicity of the surface than the free energy of particle/water/particle interaction, because in the latter case, no electrostatic repulsion is taken into account in the calculations.

The surface of oxygen-plasma-treated polystyrene (PSox) was investigated using X-ray photoelectron spectroscopy (XPS), streaming potential measurements and a dynamic study of the wetting properties at different pH (Wilhelmy plate method). The PSox surface is functionalized with various oxygen-containing groups, including carboxyl functions, and must be viewed as covered by a polyelectrolyte which swells depending on pH. The wetting hysteresis, its evolution upon repeated cycles and the influence of pH are controlled by the dissolution of functionalized fragments and the retention of water upon emersion; the retained water may evaporate progressively and allow macromolecule compaction and/or reorientation. Modification of the PSox surface upon aging in dry atmosphere, humid atmosphere, and water was studied using XPS and dynamic wetting measurements. Aging in water provoked the dissolution of PSox macromolecular chains, as indicated by adsorption of released fragments on a check PS sample placed nearby. However, the concentration of functionalized molecules at the surface of water-aged PSox was still sufficient to allow swelling at pH 5.6 and 11.0. Hydrophobicity recovery was faster in humid air (R. H. 95%) compared to dry air (R. H. 5%), due to the plasticizing effect of water. Hydrophobicity recovery upon aging in air was reversed quickly by immersion at pH 5.6 or 11.0, due to deprotonation and swelling.

Cleanliness can be characterized in industrial applications via "simple" wettability measurements, and has been successfully done so for at least two centuries. A problem in much of general manufacturing and maintenance industries is not that more sophisticated measurement and evaluation technology is necessary to provide value, but that technology developed at least several generations ago has not been more widely and profitably used. This paper describes and references that technology, and identifies published case histories where it has been both successfully and unsuccessfully used.

Static and dynamic contact angles of aqueous solutions of three surfactants--anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (DTAB), and nonionic pentaethylene glycol monododecyl ether (C(₁₂)E(₅))-were measured in the pre- and micellar concentration ranges on polymer surfaces of different surface free energy. The influence of the degree of substrate hydrophobicity, concentration of the solution, and ionic/nonionic character of surfactant on the drop spreading was investigated. Evaporation losses due to relatively low humidity during measurements were taken into account as well. It was shown that, in contrast to the highly hydrophobic surfaces, contact angles for ionic surfactant solutions on the moderately hydrophobic surfaces strongly depend on time. As far as the nonionic surfactant is considered, it spreads well over all the hydrophobic polymer surfaces used. Moreover, the results obtained indicate that spreading (if it occurs) in the long-time regime is controlled not only by the diffusive transport of surfactant to the expanding liquid-vapor interface. Obviously, another process involving adsorption at the expanding solid-liquid interface (near the three-phase contact line), which goes more slowly than diffusion, has to be active.

Detailed physical and chemical surface characterization of fractured adhesive joints, guided by qualitative fracture mechanics theory, constitutes a semiempirical method to elucidate adhesive bonding phenomena. Inherent flaws, interfacial separation, viscoelastic and plastic responses, and crazing and crack propagation are the main factors governing overall bond strength. Surface analyses (primarily by SEM/EDAX² and ESCA³) provide an estimate of the nature and extent of each mechanism. Results from various fluoropolymer joints are presented and rationalized in terms of the elastic modulus and fracture work in the failure zone. Bond strength on untreated fluoropolymers is negligible, but ESCA shows a small amount of fluorocarbon transfer to the adhesive. Surface treatments increase surface energy via a hydrocarbon layer ∼20 to >500 Å thick, and useful peel strength results. SEM shows fracture relatively deep in the fluoropolymer with pronounced microdeformation. When the surface treatment is depleted by heat or light, bond strength varies with surface composition. Also, copolymers with perfluoropropylvinyl ether side chains in place of perfluoromethyl groups are superior hot melt adhesives. The combination of SEM and ESCA shows cohesive failure in both instances, but the latter separates closer to the interface and with relatively little deformation.

Acid–base interactions across interfaces are shown to have predictable influences on adhesion. The history of this development, and methods to assay the acid–base character of solvents, polymers and a variety of powders and fibers are reviewed briefly. Recent studies are described that demonstrate directly how acid–base interactions influence both ‘fundamental’ and ‘practical’ adhesion.

The role of Lewis acid-base interactions at the fiber-matrix interface in composites is studied with both glass and Teflon fibers. In the glass fiber case, surface chemistry is modified with amino-, methacryloxy- and glycidoxy-silane coupling agents (A-1100, A-174 and A-187, respectively). Silane adsorption mechanisms as well as the properties of filament-wound, unidirectional epoxy and polyester composites are explained by a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and flow microcalorimetry. The heats of adsorption of pyridine and phenol prove that the coupling agents add acidic sites to the glass fiber surface as well as stronger basic sites. The subsequent adhesion of the matrix polymers and the short beam shear strengths of composites are explained on this basis. The Teflon fibers are first etched with sodium naphthalene solutions, and then sequentially hydroborated and acetylated, producing approximately monofunctional hydroxyl (acidic) and ester (basic) groups on the surfaces, as determined by XPS, FTIR, and electrophoretic mobility analyses. Composites prepared with the acetylated fibers and a chlorinated polyvinyl chloride (acidic) matrix are superior in tensile properties, and SEM fractography shows PTFE fibrillation, indicative of good fiber-matrix adhesion and stress transfer, in this case only.

By combining four techniques—X-ray photoelectron spectroscopy (ESCA), soft X-ray spectroscopy, contact-angle hysteresis, and electron microscopy—a powerful method to elucidate the nature of solid surfaces is created. ESCA provides semiquantitative elemental analysis of the uppermost 5–100 Å of the sample. Soft X-ray spectroscopy extends the elemental analysis to a depth of about a micron. Contact-angle measurements can be interpreted in terms of the distribution of surface energy and roughness, and a view of the microtopography is obtained with the electron microscope. This method of surface characterization has been applied to several problems in fluoropolymer surface chemistry. For example, certain sodium complex solutions are shown to react with fluoropolymer surfaces, removing most of the fluorine and leaving a sponge-like surface with characteristics of an unsaturated, oxidized hydrocarbon. Also analyzed are surface changes that occur upon exposure of these sodium-etched films to environmental conditions. In another application, films of poly(tetrafluorethylene/hexafluoropropylene) melted and recrystallized against a gold substrate were analyzed. The unusual wettability of such films has been attributed to the presence of a “transcrystalline” surface region, but our analysis indicates the presence at the surface of a very thin layer of materials with the characteristics of an oxidized hydrocarbon. The increased wettability is evidently due to the presence of this layer.

Amorphous and graphitic carbon fibers and film surfaces are characterized by wettability measurements and surface energy analysis which isolate the (London-d) dispersion γ^d _svand (Keesom-p) polar γ^p _sv contribution to solid-vapor surface tension γ_sv =γ^d _sv + γ^p _sv Graphitized carbon fibers which are surface treated to provide strong bonding to polar matrix resins show consistent strong polar contributions to total surface tension with γ^d _sv|γ_sv ≃ γ^p _sv|γ_sv ≃ 0.50. Amorphous carbon films prepared for biological implant applications display dominant dispersion character in surface energy with γ^d _sv|γ_sv ≃ 0-74 to 0.95 and γ^p _sv|γ_sv ≃ 0.05 to 0.24.

With increasingly stringent EPA guidelines for controlling emissions of volatile organic compounds on the horizon, the desirability to move to water-based printing inks is evident This paper examines the effects of corona discharge treat ments which are commonly used to improve ink adhesion to polvethylene. Electron spectroscopy for chemical analysis (ESCA) was used to determine the surface chemi cal changes induced by corona treatments in pure polyethylene extruded films and in formulated resin systems This data was correlated with surface tension and ink adhesion measurements to show the effects of treatment and additives on the final printability of the films with particular emphasis on water-based inks. In addition, the effects of stonng treated film prior to printing and of retreating these films were also examined The results of these tests have shown that formulated linear low den sity polyethylene (LLDPE) films treat and print at least as easily as high-pressure low-density polyethylene (HP-LDPE) counterparts.

We report on the surface modification of Sylgard-184 poly(dimethyl siloxane) (PDMS) networks by ultraviolet (UV) radiation and ultraviolet/ozone (UVO) treatment. The effects of the UV light wavelength and ambient conditions on the surface properties of Sylgard-184 are probed using a battery of experimental probes, including static contact angle measurements, Fourier transform infrared spectroscopy, near-edge X-ray absorption fine structure, and X-ray reflectivity. Our results reveal that when exposed to UV, the PDMS macromolecules in the surface region of Sylgard-184 undergo chain scission, involving both the main chain backbone and the side groups. The radicals formed during this process recombine and form a network whose wetting properties are similar to those of a UV-modified model PDMS. In contrast to the UV radiation, the UVO treatment causes very significant changes in the surface and near-surface structure of Sylgard-184. Specifically, the molecular oxygen and ozone created during the UVO process interact with the UV-modified specimen. As a result of these interactions, the surface of the sample contains a large number of hydrophilic (mainly –OH) groups. In addition, the material density within the first ≈5 nm reaches about 50% of that of pure silica. A major conclusion that can be drawn from the results and analysis described in this work is that the presence of the silica fillers in Sylgard-184 does not alter the surface properties of the UVO- and UV-modified Sylgard-184.

Etching and modification of polymers by plasmas is discussed in terms of the roles played by atomic and molecular oxygen, atomic fluorine, CF_x radicals, ions, high energy metastable species, and photons. Addition of fluorine-containing gases to oxygen can increase both 0 atom densities in the plasma and polymer etching rates. The etching rate be- havior generally exhibits a maximum at a specific concentration of this additive. Process parameters which alter the concentrations of 0 and F atoms in the plasma or affect the rate of delivery of these species to the polymer surface shift the position of this maximum with respect to feed gas composition. However, the gas composition which yields maximum rates exhibits a strong dependence on polymer structure, specifically, its degree of unsaturation. This is explained on the basis of molecular orbital (MO) arguments which predict that the surfaces of unsaturated polymers have a higher affinity than saturated polymer surfaces for atomic fluorine. Favored reaction pathways leading to volatile etching products are pro-posed based on MO calculations of relative bond strengths for various oxygenated and fluorinated organic model compounds. Although fluorine abstraction of hydrogen plays a major role in generating radical sites on saturated polymer surfaces, it is likely that etching of unsaturated moieties proceeds through a saturated radical intermediate resulting from addition reactions of fluorine atoms. Excessive amounts of fluorine in the plasma result in reduced etching rates and incorporation of fluorine and/or CF_x radicals into the polymer. Polymer film surfaces are also modified by high energy metastables and ultraviolet radiation generated from noble gas plasmas, The effect of vacuum ultraviolet radiation from helium microwave plasmas on films of polytetrafluoroethylene and polyethylene is addressed.

Webs of Kapton 200-H and Upilex-S polyimide films were treated using oxygen plasma prior to sequential sputter deposition of chromium and copper in a roll metallization system. Two plasma system configurations were employed for treatment. In one configuration, the sample traveled downstream from a microwave plasma; in the other, the web moved through a DC-generated glow discharge. For the DC-glow treatment, the potential difference between the plasma and the web, Φ_f, and relative ion densities, n+, were measured at various values of chamber pressure and DC power using a Langmuir probe. Although samples treated downstream from the microwave plasma were not subjected to bombardment by energetic ions, Φ_f for the DC-glow operating conditions was between 5 and 13 eV. For both films, advancing DI water contact angles of less than 20° were achieved using both modes of treatment. Contact angles for untreated films were greater than 60°. However, 90° peel tests yielded values of 15 to 20 g/mm for microwave plasma treatments and 40 to 60 g/mm for DC-glow treatment. Peel values for untreated Kapton and Upilex films were about 25 g/mm. High-resolution X-ray photoelectron spectroscopy in the C1s region for Kapton film surfaces treated downstream from the microwave plasma showed increases in carbonyl groups, with concentrations inversely proportional to web speed. In contrast, DC-glow modification was due mainly to formation of carboxylates with a small increase in carbonyl component. It is proposed that treatment downstream from the microwave plasma results in formation of a weak boundary layer at the polyimide surface. Ion bombardment occurring in the DC-plasma configuration results in relatively more crosslinking at the polymer surface. Furthermore, adhesion between the sputter-deposited chromium and the DC-glow modified polyimide improved with increasing values of Φ_fn+.

A viscous-liquid drop spreads on a smooth horizontal surface, which is uniformly heated or cooled. Lubrication theory is used to study thin drops subject to capillary, thermocapillary and gravity forces, and a variety of contact-angle-versus-speed conditions. It is found for isothermal drops that gravity is very important at large times and determines the power law for unlimited spreading. Predictions compare well with the experimental data on isothermal spreading for both two-dimensional and axisymmetric configurations. It is found that heating (cooling) retards (augments) the spreading process by creating flows that counteract (reinforce) those associated with isothermal spreading. For zero advancing contact angle, heating will prevent the drop from spreading to infinity. Thus, the heat transfer serves as a sensitive control on the spreading.

In this investigation the fracture surface between bovine dentine and bovine enamel and a dental cement was observed using the scanning electron microscope at magnifications up to 10,000 ×. The results indicated that the topography of the adherend plays an important role in the formation of an adhesive bond and in the fracture pattern of an adhesive joint, even when cohesive failure is involved.

The thermodynamics of an idealized rough surface is treated, using the geometry of a vertical plate partially immersed in a liquid. Gravity is included explicitly in the theory. The results of this treatment are more general than those of previous studies and are more easily extended to other surface topographies. Some novel results are found, such as a delineation of the conditions under which a macroscopic contact angle of 180° will result from geometric properties of the solid surface. On rough surfaces consisting of material for which, if smooth, the equilibrium contact angle would be different from 90°, the slopes of the asperities will be a very important factor in determining the effective equilibrium contact angles.

Gas discharge plasma treatment can be used to modify the surface properties of biomaterials for a variety of biomedical applications. An established application is the use of oxygen and nitrogen plasmas to improve the hydrophilicity of surfaces, encouraging cell attachment and subsequent growth. The physical properties and surface chemistry of the biomaterial influences cell attachment and subsequent culture. In-situ cells are surrounded by a complex extracellular matrix (ECM) containing fibronectin, laminin, collagen types I-V, and proteoglycans. In this study, ammonia and sulphur dioxide gases have been chosen with the objective of incorporating carboxylic acid, sulphur and nitrogen containing groups on the surface.