The interfacial region of coated plastics is an example of a multicomponent polymer system. Practical adhesion, as determined by the peel test, has been found to be strongly dependent on the composition of the system and the degree of interaction between its components. Several interactions are possible during the coating process of polypropylene (PP)/ethylenepropylene-diene-monomer (EPDM) blends with chlorinated polyolefin (primer) and polyurethane (PUR) paint. Wettability, a necessary but not sufficient condition alone for molecular interdiffusion, was found to be good in all cases. The lack of interfacial adhesion between PP and PUR and between EPDM and PUR was explained by high interfacial tensions calculated from surface energetics, which, in turn, were determined by contact angle and inverse gas chromatography (IGC) measurements. The improvement of interfacial adhesion between PUR and PP by chlorinated polyolefin was explained by acid-base interactions detected by IGC. The creation of surface topography by extraction of low molecular weight fractions during the coating process does not influence the adhesion. Molecular interdiffusion was shown to be facilitated by solvents.

A review of studies of polymer-paper adhesion illustrates the thermodynamic nature of the bondability of polymers to plain, uncoated paper surfaces. The bond strength depends strongly on the chemical nature of the polymer surface and on that of the fibrous paper surface. Adhesion to paper may be characterized indirectly through thermodynamic analysis of the paper substrate, or directly through paper laminate or adhesion tape peel testing. The need for adequate paper adhesion is emphasized, particularly for some of the newer printing processes (electrophotographic and thermal imaging). It is concluded that some of the indirect methods of adhesion characterization (surface energetics analysis via contact angle measurements or the inverse gas chromatography technique) may serve to characterize paper adhesion in these processes.

This paper aims to provide an analysis of the correlation between various plasma effects on polymers exposed to atmospheric pressure plasma. The relationship linking the surface polarity, the chemical structure and composition and the crystalline/amorphous phase contribution in the surface modification mechanisms of plasma-exposed polymers is explored. Different polymers were chosen comprising of various structures, functionality, degree of oxidation, crystallinity, and were treated under a particular experimental configuration, and dielectric barrier discharge-type. The plasma parameters and the treatment settings are observed, in relation to relevant surface properties, as surface energy components, surface topography, structural changes and chemical composition, under conditions where the gaseous environment chosen, He-N₂, allows complex surface modification, by combined functionalisation and crosslinking.

In this paper, we report and discuss the results of the surface treatment, using an atmospheric pressure dielectric barrier discharge (DBD), of selected polymer films which have no bonded oxygen in their intrinsic structures. Contact angle, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) data are presented with respect to post-treatment characterisation and the dependence of these outcomes on the salient processing variables: energy dissipated, exposure duration and inter-electrode gap. Under the treatment conditions used, remarkably uniform treatment and markedly stable modified surface properties result from the test surfaces exposed to the discharge, even at transit speeds simulating those associated with continuous on-line processing. The DBD system thus described, provides chemically mild and mechanically non-destructive means of altering surface properties, targeting improved surface characteristics and potentially better application performance.

In this paper, we report and discuss a surface treatment method, using a dielectric barrier discharge (DBD) of random filamentary type. This offers a convenient, reliable and economic alternative for the controlled modification (so far, largely dependent on surface oxidation) of various categories of material surfaces. Remarkably uniform treatment and markedly stable modified surface properties result over the entire area of the test surfaces exposed to the discharge even at transit speeds simulating those associated with continuous on-line processing. The effects of air-DBD treatment on the surfaces of various polymer films and polymer-based fabrics were studied. The dielectric barrier concerned has been characterized in terms of the energy deposited by the discharge at the processing electrodes and the resultant modifications of the surface properties of the treated samples were investigated using x-ray photoelectron spectroscopy, contact angle/wickability measurement and scanning electron microscopy. The influence of the surface treatment parameters, such as the energy deposited by the discharge, the inter-electrode gap and the treatment time were examined and related to the post-treatment surface characteristics of the materials processed. Relationships between the processing parameters and the properties of the DBD treated samples were thus established. Of the three process variables investigated, the duration of the treatment was found to have a more significant effect on the surface modifications found than did the discharge energy or the inter-electrode gap. Very short air-DBD treatments (fractions of a second in duration) markedly and uniformly modified the surface characteristics for all the materials treated, to the effect that wettability, wickability and the level of oxidation of the surface appear to be increased strongly within the first 0.1–0.2 s of treatment. Any subsequent surface modification following longer treatment (>1.0 s) was less important. The modification of the surface properties also appears to be stable with time, as minimal recovery of the surface properties is shown on ageing post-treatment. The behaviour of the woven textile polymers examined was found to be very similar, under DBD treatment, to that of thin-film variants based on the same polymers. For the porous textile fabrics examined, rapid and efficient treatment (fractions of a second) on both sides of the treated samples was found to be ensured. Thereby the system regime used offers the attractive prospect of controlling the modification of non-compact materials of various texture, porosity, etc. The DBD described system thus provides a chemically mild and mechanically non-destructive means of altering surface properties targeting improved surface characteristics and potentially better application performance.

In this paper, we report and discuss the results of the surface treatment, using an atmospheric pressure dielectric barrier discharge (DBD), of selected polymer films which have no bonded oxygen in their intrinsic structures. Contact angle, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) data are presented with respect to post-treatment characterisation and the dependence of these outcomes on the salient processing variables: energy dissipated, exposure duration and inter-electrode gap. Under the treatment conditions used, remarkably uniform treatment and markedly stable modified surface properties result from the test surfaces exposed to the discharge, even at transit speeds simulating those associated with continuous on-line processing. The DBD system thus described, provides chemically mild and mechanically non-destructive means of altering surface properties, targeting improved surface characteristics and potentially better application performance.

In this paper, continuing previous work, we report on the installation and the testing of an experimental dielectric barrier discharge (DBD) reactor run in a controlled atmospheric pressure gaseous environment other than air. Here, the effects of a N₂-DBD treatment on the surface of a test polymer material (UHMW polyethylene) are examined, reported, discussed and compared to results obtained previously following air-DBD treatment. Surface analysis and characterization were performed using x-ray photoelectron spectroscopy, contact angle measurement and scanning electron microscopy before and following the DBD processing described. The discharge parameters used were correlated with the changes in the surface characteristics found following DBD treatments of various durations in a nitrogen atmosphere. The work focuses on the control of the gaseous environment supporting the discharge and on the possibility of overcoming the potentially dominant effect of reactive oxygen-related species, derived from any residual air present. The results obtained underline the very high reactivity of such species in the discharge, but are encouraging in respect of the possibility of the implantation or generation of functional groups other than oxygen-related ones at the surface of interest. The processing conditions concerned simulate 'real' continuous high speed processing, allowing the planning of further experiments, where various gaseous mixtures of the type X + N₂ will be used for controlled surface functionalization.

Adhesion of epoxy resins on copper foils for printed circuit board (PCB) applications is improved by nearly a factor of 5, using surface cleaning and deposition of a 15-nm-thick film in a low-pressure remote plasma-enhanced chemical vapor deposition process. The cleaning pretreatment, using an N₂–O₂ oxidizing gas mixture with moderate heating (343 K), gives the best results. This pretreatment removes the carbonaceous contaminants present on the topmost surface of the sample and slightly oxidizes the copper into CuO. This oxide is then reduced during the deposition treatment, presumably by reaction with the aminopropyltrimethoxysilane (APTMS) precursor. The surface roughness is unchanged after treatment, thereby showing that the improvement of the copper/epoxy adhesion is only due to the chemistry of the plasma coating. Applying these results to dielectric barrier discharges allows us to achieve the same level of adhesion, which, therefore, does not depend on the process.

An environmentally friendly plasma amination process for the activation of polymers prior to electroless metallization using dielectric barrier discharges (DBD) at atmospheric pressure was investigated. One focus of the work was on the correlation between plasma parameters and palladium coverage on the polymer on the one hand and the palladium coverage and adhesion of a galvanic copper metallization on the other hand. Using XPS spectroscopy it was found that a DBD treatment of polyimide (PI) films with mixtures of N₂ and H₂ leads to considerably higher Pd surface concentrations than on untreated reference samples or foils treated in air-DBD. The Pd coverages achieved result in peel strengths of a copper metallization of up to 1.4 N · mm⁻¹.

A large-volume microwave plasma (LMP) apparatus has been used to polymerize organosilicone and styrene vapors onto paper substrates. Polymerization rates were established in the active glow of the plasma and in the dark, downstream volume of the reactor. Rates decrease from about 70 Ä/s in the former to about 1 Ä/s in the latter space. Surface modifications of paper substrates were studied by measurements of contact angles, of resistivity, and of charge retention properties. Plasmapolymer layers increased water contact angles from about 45 for control paper samples to> 110 for plasma-treated specimens. Resistivity was increased by up to four orders of magnitude, and the charge retention of coated papers was increased significantly. Controlled variations of the environment into which materials were placed immediately after plasma polymerization led to changes in the property balance of paper, confirming that plasma-polymer surfaces remain in active states for some time following quenching of the plasma.

We report on the preparation of amphiphilic diblock copolymers containing a hydrophilic segment, poly(acrylic acid)(PAA), and a polystyrene hydrophobic part. We analysed, by means of contact-angle measurements, how the hydrophilic segments usually bury themselves under the hydrophobic when exposed to air to reduce the surface free energy of the system. In contrast, in contact with water, the hydrophilic blocks have a tendency to segregate to the interface. We first describe the parameters that control the surface reconstruction when the environmental conditions are inversed from dry air to water vapour. Then, annealing time, temperature, composition and size of the diblock copolymers, and size of the matrix that influenced the surface migration process are the main parameters also considered. Finally, the density of the carboxylic functions placed at the surface was determined using the methylene blue method.

The chemical and physical effects incurred at the surface of biaxially oriented polypropylene film during silent discharge plasma treatment have been investigated using XPS, NMR, TOF-SIMS, and AFM techniques. It is found that chain scission accompanied by oxidative attack leads to the formation of low molecular weight oxidized material which agglomerates into globules at the surface due to a large difference in interfacial free energy between the underlying hydrophobic substrate and the oxygenated overlayer.

The surface tension of a model, water-based, flexographic printing ink was measured at a range of surfactant concentrations along with the equilibrium contact angle formed with polymer substrates. The surface excess of surfactant at each concentration was calculated using the Gibbs adsorption isotherm and assumed equal to the concentration of surfactant at the interface. The change in the surface tension of the ink formulation was assumed to be determined entirely by the surface concentration of surfactant. This allowed the estimation of the surface tension at the solid–liquid and solid–vapour boundaries when in contact with substrate based on the values obtained for pendant drops. The associated polar and dispersive contributions to the surface tension were then calculated using the Young–Dupré equation. The values of the polar and dispersive surface tension components extracted in this manner were compared with those calculated using the approach of van Oss, Chaudhury and Good. The use of surface excess in estimating the contributions to surface tension was found to give far better agreement with experimental data than the van Oss approach which is intended for use with pure liquids.

Plasma diagnostic tools are an essential element towards the proper understanding and development of technological plasmas. Knowledge of the particle densities and energies in the bulk and at boundaries, the electrical potentials and the spatial and temporal evolution of these parameters allow technologists to operate plasmas in the most efficient way and allow the intrinsic plasma processes to be tailored to suit a particular application. There are many different diagnostic tools that can be used, depending on the type of plasma under investigation and the specific information that is required. Here, we have chosen to highlight four techniques frequently used in both academia and industrial settings. The first of these is the interpretation of the driving current and voltage waveforms. These measurements do not affect the plasma and can yield useful information on the major processes in the discharge. The second is electrical probing which, by their nature, are intrusive, since their presence affects the plasma under investigation. Their use is usually confined to low-pressure and low-temperature plasmas in which the heat flux will not destroy the integrity of the probe. The third area is mass spectrometry, which is most often performed at the substrate or plasma boundaries and may in many cases not affect the plasma unduly. The fourth diagnostic method discussed, optical emission spectroscopy, is non-perturbing; however, interpretation of spectral response is often difficult in low-pressure plasmas where the species are not in local thermodynamic equilibrium.

Cellulose is a biodegradable, renewable, flexible, inexpensive biopolymer that is abundant in nature. However, due to its hydrophilicity, applications of cellulose (paper) in the handling of liquids are severely limited. Appropriate plasma-or glow discharge-assisted processing sequences can be used to modify the surface of cellulose/paper so that the interaction of liquids with these surfaces can be altered. In particular, nanostructures associated with crystalline regions of cellulose fibers can be uncovered by plasma-enhanced etching; subsequent plasma-enhanced fluorocarbon film deposition (~ 100 nm) converts the surface into a superhydrophobic (static water contact angle> 150o; receding contact angle< 8o) state. Similar results can be obtained by depositing diamond-like carbon films on the plasmaetched surface, in spite of the inherently hydrophilic nature of diamond-like carbon itself. In addition, droplet adhesion and mobility can be controlled; depending on the etch cycle parameters, the paper surface can be rendered ‘roll-off’or ‘sticky’superhydrophobic. Use of a commercial printer to generate hydrophobic ink patterns on superhydrophobic paper surfaces allows controlled movement, transfer and storage of water or other aqueous liquids on the paper surface. These basic functionalities can be combined to design simple two-dimensional lab-on-paper (LOP) devices. Finally, by controlling both the cellulose fiber size and spacing, and depositing a fluorocarbon film, paper surfaces can be rendered superomniphobic, repelling both polar and apolar liquids.

Oxygen plasma treatment can be used for increasing the hydrophilicity of polymer surfaces, however, it is widely known that this effect decays significantly with time. This ageing phenomenon is thought to be caused by both migration of low molecular weight fragments and reorientation of modified polymer chains. It has recently been shown that the aged surface becomes transiently hydrophilic before attaining a final surface energy significantly lower than the initially treated surface. X-ray photoelectron spectroscopy (XPS) and contact angle measurements were used to monitor the changes in surface chemistry of plasma oxidized poly(ether ether ketone) (PEEK) during post treatment storage. The decay and transient increase in hydrophilicity were found to be dependent upon crystallinity and storage temperature.

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.

Pretreatments of polyolefins and fluoropolymers are usually necessary to achieve satisfactory adhesion for bonding and related technologies. In this paper results for various pretreatments of these polymers are presented. These are the treatment of polyolefins with aqueous reagents, dilute fluorine and a natural gas flame, the treatment of PTFE with sodium naphthalenide and the treatment of ECTFE with sodium naphthalenide and a flame. X-ray photoelectron spectroscopy was used to investigate the chemical changes caused by the treatment and the adhesion levels were discussed in relation to wetting, interactions across interfaces and weak boundary layers.

A comparative study of the treatment of polytetrafluoroethylene (PTFE) and poly(vinyl fluoride) (PVF) with “Tetra-Etch” has been carried out. The treatment of PTFE resulted in extensive changes in surface chemistry and topography, whereas with PVF there was no significant change in topography and the chemical changes were much less marked. However, treatment of both polymers resulted in large increases in bond strength.

Multiple bonding experiments in which samples are repeatedly fractured and re-bonded were carried out with untreated PTFE and PVF. These resulted in moderate increases in bond strength with PTFE and large increases with PVF. The results indicate that weak boundary layer (WBL) removal is a key element in adhesion improvement by “Tetra-Etch” on PVF. With PTFE, WBL removal also improves adhesion, but the chemical and/or topographical changes introduced by the “Tetra-Etch” are required for optimum performance.

Surface pretreatment methods to enhance adhesion to polymers with low surface energies generally either remove a region of low strength from the surface or introduce new surface functional groups. The relative importance of these two mechanisms is examined in the present paper for various combinations of pretreatment and polymer.

Adhesion to polyethylene and polypropylene is a complex subject requiring understanding of (a) the poor adhesive characteristics of these polymers; (b) the superior performance following certain pretreatments and (c) the nature of the changes brought about by these pretreatments and the mechanisms involved. This review discusses work on these topics and examines the impact of recent data resulting from the application of surface analytical techniques. The roles of ‘weak boundary layers’, surface energy and wettability and specific interactions are discussed in some detail.

In the last 25 years, surface sensitive analytical techniques have made a major contribution to our understanding of adhesion phenomena and problems. There are several areas where these techniques have provided important information including the identification of failure modes, the chemistry of a substrate before and after pretreatments, the stability of surfaces and interfaces, the identification of surface contaminants, the interaction across an interface and the nature of interphases. X-ray photoelectron spectroscopy (XPS or ESCA), Auger electron spectroscopy (AES) and static secondary ion mass spectrometry (SSIMS) have proved to be especially useful. Many examples of the usefulness of these techniques are given.

The most effective commercial methods for pretreating fully fluorinated polymers at present are sodium in liquid ammonia and sodium naphthalenide in a solvent such as tetrahydrofuran. A number of other methods can produce large increases in bondability but are relatively inefficient. Plasma treatments of fully fluorinated polymers such as PTFE often introduce functional groups and/or increase wettability but result in moderate improvements at best in bondability. However, recent work with ammonia plasmas has resulted in big improvements in bondability. Some batches of partially fluorinated polymers may be effectively bonded without a pretreatment. However, other batches possess surface regions of low cohesive strength. Partially fluorinated polymers such as poly (vinyl fluoride) may be rapidly and effectively treated with a conventional flame treatment. Where a flame treatment is unsuitable, as with complex shapes, potassium hydroxide solutions provide effective treatments for partially fluorinated polymers such as poly (vinyl fluoride) and poly (vinylidene fluoride).

Good adhesion to polymers is required in a number of important technologies including adhesive bonding, printing, and painting. To achieve a satisfactory level of adhesion it is often necessary to pretreat the polymer by one of a wide range of methods. Two books are of particular interest [1, 2]. In the case of polar polymers such as nylon 66 and epoxide thermosets, a treatment may not be necessary, or if the surfaces are contaminated, a physical method such as solvent degreasing or grit blasting to remove the contaminants may be all that is required. On the other hand, if a polymer lacks suitable functionality, it will be necessary to modify its surface chemically. Polymers with no active functionality include low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP). A wide variety of methods for introducing new groups is available, including the use of low-pressure plasmas, corona discharges, flames, etchants, and active gases. Flame treatment to enhance adhesion to polymers has been used since the early 1950s, one of the first applications being to enhance print adhesion to lowdensity polyethylene. Since that time, flame treatment has been used with many other polymers in a variety of applications. Flame treatment has a number of advantages over the other main method of treating large areas of polymers, ie, the corona treatment. These include no reverse-side treatments, no creation of pinholes, no Ozone production, and better aging characteristics.

Surface and interface characterization of polymeric materials has not enjoyed the multi-technique approach which typifies other types of materials. X-ray photoelectron spectroscopy (XPS) has dominated, despite several major disadvantages. New approaches are discussed which either improve XPS (particularly derivatization techniques) or utilize ‘static’ secondary ion mass spectrometry (SIMS) to overcome these limitations, with examples of their application in materials problem solving.