Paper, although ubiquitous, is a complex material. We can classify paper as a basic network of self bonding cellulosic fibers; the chemical and physical characteristics of its surface are controlled by the raw materials, papermaking and converting processes used to produce it. Paper sometimes contains non-cellulosic fibers such as non-wood and synthetic fibers, chemical additives, fillers, and bonding agents. Other chemical additives used in the papermaking process, e.g., formation, drainage, and retention aids or coating materials may also change the physical and chemical characteristics of the paper's surface. With the greater use of recycled fibers we may expect additional changes in surface chemistry and structure.

The popularity of surface engineering has increased significantly over the past 10 years. This is usually owed to the fact that, in many instances, no more can be done to improve a material's adhesion performance through manipulation of the bulk material. Due to this, many industrialists and academics are turning their attentions to controlling material surfaces to optimize their properties, including wettability and adhesion. With its numerous benefits, when it comes to materials processing, laser surface engineering is now becoming more widely used to bring about the necessary required surface modifications for a wide range of applications such as biomedical, microbiological, tooling, battery development and for applications in the electronics industry. This Chapter discusses the implementation of lasers for the surface engineering of polymeric materials along with contact angle goniometry and tensiometry, two common methods for analysis of the wettability and adhesion of materials that will lead to the unlocking of new knowledge about wetting and adhesion regimes.

X-Ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS) were used to study the chemical modification of polyphenylene sulfide (PPS) thin films on exposure to both oxygen and ammonia plasmas. The XPS results for the oxygen plasma treatment indicated a large oxygen increase with the incorporation of various oxidized carbon species as well as oxidized sulfur. For the ammonia plasma, both nitrogen and oxygen were incorporated. IRRAS proved to complement the XPS results, showing a wide range of C O and CO functionalities incorporated on oxygen plasma exposure. For the ammonia plasma treatment, an increase in hydrocarbon, alkene-type fragments, and possibly amine groups was detected. Both the XPS and IRRAS results indicated that exposure of plasma-treated surfaces to epoxy with subsequent carbon tetrachloride washes removed most of the modification originally present after plasma treatment. IRRAS analysis showed that a thin layer of epoxy remained after repeated solvent washes and that the film seemed to be cured. For untreated PPS films, a non-cured epoxy film adsorbed. This work suggests that the plasma-modified layer plays a role in the formation of a covalent interphase region between PPS and epoxy.

The wettability of materials depends strongly on their surfaces, and endowing them with expected wetting properties promotes their applications in various fields. In this work, the biodegradable and superhydrophilic poly(butylene succinate) (PBS) nanofibrous membranes were fabricated using a combination of electrospinning and oxygen plasma treatment for the first time. The surface morphologies, chemical composition and wettability of the PBS membrane were investigated. It was found that the plasma etched the fiber surface and the etching depth increased with the plasma treatment time. The membrane became superhydrophilic from hydrophobic upon treated with oxygen plasma and the water droplet could completely spread out within 0.5 s, which was mainly attributed to the introduction of oxygen-containing groups by plasma treatment rather than the enlarged surface roughness. Meanwhile, the speed of water spread out on the modified membrane was closely and reversely related to the density of membrane. The wettability differences between nanofibrous membrane and dense films were also pointed out, and the structure had great influence in the performance. Furthermore, the wetting stability of treated membrane was explored by monitoring the evolution of contact angle. The contact angle gradually increased with days due to the decreasing functional groups, and the ageing rate was dependent on the plasma exposure time. Even though the wettability of membranes changed fast in the first 10 days, surfaces were still remained moderately hydrophilic (contact angle ~50°) after a month. The investigation concentrated on the wettability of PBS nanofibrous membrane treated with oxygen plasma is beneficial to the creation of materials with desirable properties for various applications.

THE nature of active nitrogen, the mechanism of its afterglow¹, and its gas phase reactions with organic molecules² have been discussed. I have now investigated a heterogeneous active nitrogen reaction at a polymer surface.

The surface of polyether ether ketone (PEEK) films was modified using plasma treatment, corona, or surface etching to improve their adhesion with regard to glued copper foils and copper layers generated by physical vapor deposition. After the pretreatments, surface chemical analysis was performed by X-ray photoelectron spectroscopy (XPS). The wetting behavior was qualitatively investigated by contact angle measurements. Surface topography was monitored by laser scanning microscopy (LSM). After coating, the adhesion strength of the copper layer was measured by a peel force test. Plasma treatment, corona discharge, or etching lead to a significant increase in adhesion. This increase is caused by a change in surface topography as well as by the incorporation of polar groups into the surface.

Polyethylene and polystyrene film surfaces have been plasma-oxidized and subsequently characterized by X-ray core level and valence band spectroscopies. The extent of polyethylene surface oxidation was found to be dependent on the power of the oxygen glow discharge employed and the length of time that the treated sample was left exposed to air prior to analysis. In marked contrast to these observations, plasma-oxidized polystyrene surfaces were much less dependent on the oxygen glow discharge power and were also found to retain their oxygenated character over much longer periods of ageing. These differences in oxidative behaviour are explained in terms of the molecular structures of the respective polymers.

This paper studies the effects on valid domain of contact angles and error limits of solid surface tension components and parameters (SSTCPs)/square roots of SSTCPs (SQSSTCPs) from the changes in liquid surface tension components and parameters (LSTCPs) when applying the van Oss–Chaudhury–Good (vOCG) approach. The results of maximum absolute errors and maximum relative errors (MREs) in SQSSTCPs/SSTCPs, induced by errors in LSTCPs or contact angles, show that most SQSSTCPs/SSTCPs can be evaluated at moderate accuracy from the lowest condition number liquid triplets, assuming that |Δθ_i| = 1° and  = 0.1 mN/m (i = 1, 2, 3, k = LW, +, −). This confirms the validity of the vOCG approach. The accuracy of each SQSSTSCP/SSTCP declines with increasing θ_i or decreasing parameter when θ_i > 0 or a critical value, provided the other two contact angles are kept fixed. This explains the underlying reasons for negative SQSSTCPs. At the scale proposed by vOCG, dimethyl sulphoxide is not suggested for use. Comparing with the MREs obtained at vOCG scale, considering the acidity of diiodomethane improves the accuracy of ; using the scales proposed by Lee and Shen do not affect the accuracy of SSTCPs, but using the scale proposed by Della Volpe et al. improves the accuracy of SSTCPs at low θ₂ and θ₃ while declines that at high ones. For a low , low surface tension apolar liquid is preferred for high accuracy. The dependence of the accuracy of SQSSTCPs/SSTCPs on contact angles suggests the importance of considering contact angle in accuracy evaluation.

Dependence of the wetting characteristics of a solid on the roughness of its surface is inherent in the fundamental theory of wetting action (R. N. Wenzel: Ind. Eng. Chem. 28, 988 (1936)). This is immediately apparent when analyses of wetting phenomena take into account the actual areas of the several inter-faces involved as well as their respective specific energy values. The same method of analysis has led to quantitative evaluationof the effects of surface heterogeneity and surface porosity (A. B. D. Cassie and S. Baxter: Trans. Faraday Soc. 40, 546 (1944)).

In the waterproofing of light-weight I woven or knitted fabrics, it is generally essential to preserve the airporosity of the material. The waterproofness that can be effected is therefore definitely limited by the size of the openings, because water will readily pass through if the pressure behind it is sufficient to break the surface film across the openings. Water will penetrate, however, at a much lower pressure or even against pressure, if it can spread over the surface of the threads from one face of the cloth to the other. The waterproofing of open fabrics, therefore, presents the problem of preventing this spreading of water over the thread surfaces. The desired effect is attained by depositing on the fabric some chemical substance that has of itself this ability to resist wetting.

For practical reasons, preparations intended for use in waterproofing open fabrics commonly consist of emulsions. In these preparations the active water-repellent agent is combined with other ingredients whose presence is required to ensure the desired fluidity and stability in the emulsion, to provide proper pH control, to increase the permanence of the proofing effect, and to modify the appearance and feel imparted to the finished fabric. These auxiliary constituents may impair, or they may enhance, the effectiveness of the proofing treatments. The complexity of the problem thus presented makes it desirable to study carefully the wetting characteristics of materials selected for this use.

In recent years, we have witnessed a remarkable growth in the use of the synthetic organic polymers in technology, both for high-technology and for consumerproduct applications (see Fig. 1 [1]). Polymers have been able to replace more traditional engineering materials such as metals, because of their many desirable physical and chemical characteristics (high strength-to-weight ratio, resistance to corrosion, etc.) and their relatively low cost. However, fundamental differences between polymers and other engineering solids have also created numerous important technical challenges, which manufacturing operations must overcome. An important example is the characteristic low surface energy of polymers and their resulting intrinsically poor adhesion [2–6]; the term “adhesion,” as it is used here and elsewhere in this text, may be briefly defined as the mechanical resistance to separation of a system of bonded materials [7]. Because adhesion is largely a surface property, often governed by a layer of molecular dimensions, it is possible to modify this near-surface region without affecting the desirable bulk properties of the material.

Low-pressure plasma processing of materials can be divided into three categories, namely (A) etching (removal of material),(B) deposition (addition of new material to a surface), and (C) modification (morphological, structural, and physicochemical change of the surface or near-surface region). In industries which make extensive use of low-pressure plasmas (for example, in the manufacture of integrated circuits-IC, the treatment of polymers for improved adhesion, etc), the above-named changes are deliberate and highly beneficial. However, there exist many instances where treatment can turn into a liability, or where plasma-chemical changes occur involuntarily and are a priori detrimental. The main objective of this chapter is to sensitize the reader to the existence of circumstances where plasma effects can be deleterious, for example:(1) Corona discharges, also known as silent discharges or dielectric barrier discharges, are a form of plasma which occurs when insulating materials are exposed to an alternating source of high voltage (~ 10 kV). Corona is comprised of multitudes of ultra-rapid (~ 100 ns), narrow (~ 100 μm) filamentary micro-discharges, which impinge upon the dielectric surface. Since the 1950s corona is being used commercially for treating polymeric webs up to 8 m in width, so as to render them printable (process category (C) above). However, corona treatment (like its low-pressure counterpart) can be detrimental if" overtreatment" occurs: If the reagent gas, like ambient air, contains oxygen, low-molecular-weight oxidized materials (LMWOM) form on the surface, and these can give rise to a weak boundary layer. This laboratory has compared corona and glow discharge treatment of LDPE and PET, using peel strength and XPS measurements, and has found similar" optimum" treatment criteria for both types of processes: High treatment (oxidation) levels could be correlated with elevated concentrations of acidic (O= C-O) reaction products and low peel strength.(2)

Low-temperature radiofrequency excited gas plasma was applied to the surfaces of a number of polymers. Polymers that are known to crosslink as well as those that only degrade under irradiation were included in the investigation. Surface changes were studied by viscosity, gel content, and contact-angle measurements. Changes in adhesive bond strength were used as a measure of overall practical effects of plasma treatment. In each case the response of the polymer surface to an oxidizing (oxygen) and a nonoxidizing (helium) plasma environment is discussed. Further indications of the nature of the surface changes were suggested by statistical treatment of the bond-strength data.

The study of the ionization of carboxylic acid groups at the interface between organic solids and water demonstrates broad similarities to the ionizations of these groups in homogeneous aqueous solution, but with important systematic differences. Creation of a charged group from a neutral one by protonation or deprotonation (whether -NH₃⁺ from -NH₂ or -CO₂- from -CO₂H) at the interface between surface-functionalized polyethylene and water is more difficult than that in homogeneous aqueous solution. This difference is probably related to the low effective dielectric constant of the interface (ε≃9) relative to water (ε≃80). It is not known to what extent this difference in ε (and in other properties of the interphase, considered as a thin solvent phase) is reflected in the stability of the organic ions relative to their neutral forms in the interphase and in solution, and to what extent in differences in the concentration of H⁺ and OH- in the interphase and in solution. Self-assembled monolayers (SAMs)-especially of terminally functionalized alkanethiols (HS(CH₂)_nX) adsorbed on gold-provide model systems with relatively well-ordered structures that are useful in establishing the fundamentals of ionization of protic acids and bases at the interface between organic solids and water. These systems, coupled with new analytical methods such as photoacoustic calorimetry (PAC) and contact angle titration, may make it possible to disentangle some of the complex puzzles presented by proton-transfer reactions in the environment of the organic solid-water interphase.

This paper reports on a three-part study: (1) to determine the effect of surface pretreatment of BDS, a siloxane/polyimide copolymer, on adhesion; (2) to determine the extent of segregation of components of BDS against metal substrates; and (3) to determine the properties of ultrathin polymer films against metal substrates.

Surface pretreatment of bds films with aqueous NaOH etched away the top siloxane layer, roughening the polymer surface and producing surface functional groups. These changes resulted in increased wettability and peel strength. Siloxane segregation when bds films were formed against metal surfaces was in the order: Al > Ti > Zn. The relative acidity of the metal oxides as measured by polyvinyl chloride adsorption was in the same order. Reflection-absorption measurements using Fourier transform infra-red spectroscopy were found to be useful in studying the crystallinity of thin polyphenylene sulphide (pps) films. X-ray photoelectron spectroscopy was used to show that failure occurred through a thin layer of residual pps polymer close to the copper oxide substrate.

A meat product package including an enclosing film having an EVA-containing inside surface and an in situ aqueous medium-cooked meat product in adhering relation to the film inside surface as the meat contacting and adhering surface. Starch particles are preferably dispersed across the meat contacting surface which has been both irradiated and subjected to corona treatment. A method for corona treating a thermoplastic tube inside surface in which small particles within the flat tube separate opposite surfaces providing voids, and the electric discharge crosses the flat tube through the voids.

The sessile drop contact angle measurement is a useful and reliable method for surface energy determination and cleanliness verification. A review of the available methods, commercial instruments, patents, and literature describing the state of the art in contact angle measurement is followed by a description of contact angle measurement techniques that have been modified for use on large surfaces. The negative effects of these changes on accuracy and precision are discussed, and remedies are proposed including the use of standard reference objects that mimic the size and shape of sessile drops. The combination of these validation tools and the modified contact angle measuring techniques fills a need for robust, production-line capable cleanliness verification methods.

An apparatus and method are provided for surface treating the inside surfaces of hollow or three dimensional plastic objects. While the invention will be described with respect to plastic objects, it will be understood that other objects having a high dielectric strength, such as ceramics, cardboard, paper and wood, may be similarly treated. The surface treating is effected by selectively directing a high voltage plasma field to a selected interior surface of the object to enhance adhesion of various glues, inks and the like. The plasma field is generated in the interior of a tunnel directed into an opening of the hollow portion of the object to be treated. A specially designed electrode is supported from the opening to direct in a controlled manner the field to the selected interior area of the object to be treated. The electrode is supported from a high dielectric shield covering a central area of the opening to direct the plasma field around the shield to a laterally extending electrode below the shield. The electrode is supported from the shield by a conductive rod and is fashioned to extend in a spaced relation to the interior of the object to provide a proper energy level in the plasma to the area to be treated. A plurality of electrodes may be utilized to treat separate and selected interior areas of the object.

Apparatus and method for treating the interior surfaces of hollow plastic objects to improve their adherency to and compatibility with another component, such as polyurethane foam. The invention consists of creating a vacuum in the object and drawing a conductive gas inside the object. A pair of electrodes are spaced apart from each other, and a source of electricity is provided thereto of sufficient intensity to produce an electrical discharge across the gap between the electrodes when an object is in the gap between the electrodes. The electrodes are arranged with regard to the size and configuration of the object to provide ionization of the conductive gas inside the object to surface treat the inner walls.