Metallized polymer or polymer-based materials are used in a large range of electronics applications including the fabrication of ohmic contacts, chip-level interconnects, printed circuit boards and shielded materials.^1–7 For such technological applications, electroless deposition is the most widely used method in practice today.⁸ Basically, electroless plating is an autocatalytic redox process occurring in aqueous solution between ions of the metal to be deposited (generally Ni or Cu) and a strong reducer. Typical procedures involve a variety of multi-step sequences for the preparation of the surfaces to be coated. Conventionally, substrates are cleaned with solvents to remove surface contaminants, chemically etched to obtain a micro-roughened oxidized surface, and then seeded with a catalyst such as palladium. Chronologically, the seeding process was first accomplished by using a two-step procedure involving substrate treatment successively in dilute SnC1₂ (sensitization step) and PdC1₂ (activation step) acidic solutions. Further, a one-step procedure using a colloidal suspension containing both Sn and Pd species (a SnC1₂/PdC1₂ acidic solution) has been developed and is presently in common use in industrial environments. In this last case, the Pd/Sn colloidal particles adsorbed on the polymer surface must be exposed (acceleration step) to a solubilizer (a HCl or NaOH solution) to remove the excess of Sn⁺² species surrounding the catalytic Pd-based core of the colloidal particles. As can easily be inferred from the details of such multi-step procedures, it is today highly desirable to develop alternative approaches for making the insulating surfaces catalytically active. These approaches should require no chemical surface etching, reduce the number of process steps, and provide a highly selective, well-defined interaction between the catalytic species and the surface to be coated.⁹

The effectiveness of the treatment with ultraviolet light (UV) on several polymeric surfaces has previously been established. In this study, a low pressure mercury vapour lamp was used as a source of UV radiation for the surface treatment of a difficult-to-bond block styrenebutadiene-styrene rubber (S6), the treatment time ranging from 10 s to 30 min. The UV-treated S6 rubber surfaces were characterized by contact angle measurements (ethylene glycol, 25°C), ATR-IR spectroscopy, XPS, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). T-peel tests on UV-treated S6 rubber/polyurethane (PU) adhesive/ leather joints (before and after ageing) were carried out to quantify adhesion strengths. The UV treatment of S6 rubber produced improved wettability, the formation of CO, CO and COO moieties, and ablation (removal of a thin rubber layer from the surface). The extent of these modifications increased with increasing treatment time. The extended UV treatment produced greater surface modifications, as well as the incorporation of nitrogen moieties at the surface. Furthermore, noticeable ablation of S6 rubber surface occurred. Peel strength values increased with increased treatment time of UV treatment of S6 rubber. Also, with increasing treatment time, the adhesive joints showed different loci of failure: adhesional failure for the as-received and 2 min-UV treated S6 rubber/polyurethane adhesive/leather joints changed to mixed failure (cohesive in the treated S6 rubber + adhesional failure) for the 30 min-UV treated S6 rubber/polyurethane adhesive/leather joint.

A styrene-butadiene-styrene (S6) rubber was treated with corona discharge to increase its surface energy and adhesion to polyurethane (PU) adhesive. The influence of the length of treatment (the speed of the upper plate was varied from 80 to 900cm/min) during corona discharge was analyzed. The corona energy applied to S6 rubber surface ranged from 0.4 to 4.6J/cm ² . The surface modifications produced as a consequence of the corona discharge were characterized immediately after treatment was carried out and were monitored by means of different surface analysis techniques, mainly contact angle measurements (ethylene glycol, 25 ^o C), ATR-IR spectroscopy, XPS and Scanning Electron Microscopy (SEM). T-peel tests of corona-discharge-treated S6-rubber/polyurethane (PU) adhesive/leather joints (72h after joint formation) were carried out to evaluate the influence of the surface modifications produced by the corona discharge on the adhesion properties of the treated S6 rubber.The corona discharge improved the wettability of the S6 rubber due to the formation of polar moieties, mainly C-O, C=O and COO ^- groups. These chemical modifications were not detected by ATR-IR spectroscopy (depth of analysis about 5μm), indicating that a nanometer-range oxidized layer was created on the S6 rubber surface by treatment with corona discharge. Besides, surface cleaning and removal of rubber contaminants (mainly silicon moieties) were produced but roughness was not created as a consequence of the treatment. These modifications were enhanced when a low speed treatment (long treatment and high corona energy) was carried out. Peel strength values of corona-discharge-treated S6 rubber/PU adhesive/leather joints only moderately increased (mainly for long length of the corona discharge). Although corona treatment chemically modified the surface of the S6 rubber, the absence of surface roughness might likely be responsible for the slight improvement in its adhesion properties.

SBS rubbers containing different loadings of calcium carbonate and/or silica fillers were surface treated with UV-ozone to improve their adhesion to polyurethane adhesive. The surface modifications produced on the treated filled SBS rubbers have been analyzed by contact angle measurements, ATR-IR spectroscopy, XPS and SEM. The adhesion properties have been evaluated by T-peel strength tests on treated filled SBS rubber/polyurethane adhesive/leather joints. The UV-ozone treatment improved the wettability of all rubber surfaces, and chemical (oxidation) and morphological modifications (roughness, ablation, surface melting) were produced. The increase in the time of UV-ozone treatment to 30 min led to surface cleaning (removal of silicon-based moieties) due to ablation and/or melting of rubber layers and also incorporation of more oxidized moieties was produced. Although chemical modifications were produced earlier in an unfilled rubber for short time of treatment with UV-ozone, they were more noticeable in filled rubbers for extended length of treatment, mainly for S6S and S6T rubbers containing silica filler. The oxidation process seemed to be inhibited for S6C and S6T rubbers (containing calcium carbonate filler). On the other hand, the S6S rubber containing silica filler and the lowest filler loading showed the higher extent of modification as a consequence of the UV-ozone treatment. The UV-ozone increased the joint strength in all joints, more noticeably in the rubbers containing silica filler, in agreement with the greater extents of chemical and morphological modifications produced by the treatment in these rubbers. Finally, the nature and content of fillers determined the extent of surface modification and adhesion of SBS rubber treated with UV-ozone.

A remarkable agreement between Weber's linear analysis and experiment makes it possible to determine the dynamic surface tension of viscous liquids from the growth rate of axisymmetric disturbances on excited capillary jets. The method is very accurate and can be used to determine the surface tension at as short as 10⁻⁴ sec surface age. Aqueous glycerol solution and inks developed for inkjet printing were used as test liquids in the experiments. While a dye base ink showed time-dependent surface tension, the surface tension of inks which were colloid suspensions of small pigment particles and contained surfactant micelles equalled their equilibrium value at 10⁻⁴ sec surface age. In the tentative explanation of this phenomenon, the dynamic equilibrium between surfactant molecules in solution and in micelles was substituted for long-range surfactant transport by diffusion. A result of this assumption is that surface tension in nonequilibrium states depends only on the composition of the surface layer.

The purpose of this research was to classify fluoropolymer surfaces with regard to their wettability by various liquids. Thin solid blades, coated with various fluoropolymers, were suspended from a force transducer balance. The blades penetrated various hydrocarbon/air and hydrocarbon/water interfaces, and the curves of force acting on the blade versus displacement were recorded. The contact angles hydrocarbon/solid/air and hydrocarbon/solid/water were calculated using: $\text{COS}\text{θ =}\text{t}\text{γL}$ and $\text{COS}{}_{\mathrm{i}}\text{θ =}\text{T}{}_{\mathrm{i}}\text{γi}$ where θ, θ_i: contact and interfacial contact angle; γL, γi: surface and interfacial tension; and τ, τ_i: adhesion and interfacial adhesion tension. Cos θ versus γ_L for various γ_L were plotted and γ_c (for cos θ = 1) was determined. It was found that there are two critical surface (γ_c) and critical interfacial (γ_cⁱ) tensions due to contact angle hysteresis. Three different fluoropolymer surfaces were investigated. When the surface can be used in the form of a well-defined blade and when enough liquid to be tested is available, the method was found to be useful, rapid, and reproducible. Under these circumstances it can be used in place of Zisman's well-known sessile drop method.

Electrical characterization is based on a display of voltage and charge which appears as a simple parallelogram. The area is a measure of energy input per cycle and is independent of voltage waveform but very dependent on the maximum voltage. A useful model for such corona discharges employs a Zener diode to simulate the corona drop. The buffer dielectric plays a major roll in controlling the corona power, and the air gap importance depends on the electrode system employed. Proper interpretation of the voltage-charge traces provides insight as to the corona performance and serves as a diagnostic procedure for obtaining optimum performance.

A sphere in continuum model, with an internal surface, is used to relate surface tension and internal pressure. The results support the previous use of this model for polar interactions. The agreement of theory and experiment is close to that obtained with a recent lattice model.

A technique for generating active species with the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) has been developed and used to sterilize and increase the surface energy, wettability and wickability of nonwoven fabrics. The OAUGDP is a non-thermal, fourth-state-of-matter plasma with the classical characteristics of a low pressure DC normal glow discharge that operates in air (and other gases) at atmospheric pressure. No vacuum system or batch processing is necessary, and a wide range of applications to fabrics and polymeric webs can be accommodated in a parallel plate plasma reactor. In addition to directly exposing webs and workpieces to active species for surface energy increase in a parallel-plate reactor, we have shown that active species capable of sterilization can be convected at near room temperature to a remote exposure chamber. This technology is simple, produces many effects that can be obtained in no other way, generates minimal pollutants or unwanted byproducts, and is suitable for online treatment of webs, films, and fabrics.

Early exposures of nonwoven fabrics to the OAUGDP required minutes to produce relatively small increases of surface energy. These durations appeared too long for commercial application to fast-moving webs. Recent improvements in OAUGDP power density, plasma quality and impedance matching of the power supply to the parallel plate plasma reactor have made it possible to raise the surface energy of a variety of polymeric webs (PP, PET, PE, etc.) to levels in the range of 60 to 70 dynes/cm with one second of exposure. In most cases these high surface energies were not durable, and fell off to 50 dynes/cm after periods of weeks to months. Here, we report the exposure of nonwoven fabrics made of PP and PET at the UTK Textiles and Nonwovens Development Center (TANDEC) to an impedance matched parallel plate OAUGDP for durations ranging from one second to several tens of seconds. Data will be reported on the surface energy, wettability and wickability as functions of time of exposure, and of the aging effect after exposure. We will report the use of a OAUGDP with air as the working gas to sterilize a broad range of microorganisms on a variety of surfaces, and in several distinct applications. These include a Remote Exposure Reactor to sterilize large workpieces 20 centimeters or more from the plasma-generating region, and a sterilizable air filter.

In this paper, we present data on the physics and phenomenology of plasma reactors based on the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP^™) that are useful in optimizing the conditions for plasma formation, uniformity and surface treatment applications. It is shown that the real (as opposed to reactive) power delivered to a reactor is divided between dielectric heating of the insulating material and power delivered to the plasma available for ionization and active species production. A relationship is given for the dielectric heating power input as a function of the frequency and voltage at which the OAUGDP^™ discharge is operated.

Different methods used to determine the surface energy of solids from the contact angles of different liquids were compared considering their theoretical background, and multicomponent approaches were applied to polymers and surface-treated polymers containing only C, H, O and N. These methods involve different approximations and give different results regarding surface energy, supporting the view that none of them provides absolute values having the accuracy expected for thermodynamic parameters and their use in computing quantities such as the work of adhesion and interfacial energy. Nevertheless they ranked the surface polarity in the same order, which was also the order simply provided by the water contact angle. A multivariate analysis of works of adhesion deduced from measured contact angles for a set of liquids on different solids may be a relevant alternative to deterministic approaches for ranking surfaces and deciphering the factors which govern their behavior. As the acid-base interactions are involved in surface energy and are due to specific chemical functions, the relationship between the water contact angle and the surface composition was examined, using surface-oxidized polypropylene as a model case. The cosine of the water contact angle was found to correlate with the “surface” oxygen concentration determined by XPS. However, this correlation may be misleading. Actually the surfaces showing the highest oxidation and the highest apparent hydrophilicity should be regarded as covered with a layer of adsorbed compounds, rather than belonging to a defined solid phase.

In the conventional methods of estimating the wetting characteristics of solids from contact angle experiments, the surface energetic properties of the solid are assumed to be identical in the environments of both the surrounding medium and probe fluids. While this assumption is suitable for solids which possess rigid surface structures (such as glasses, ceramics, and metals for example), it is generally inapplicable to polymeric solids, since the surfaces of the latter are relatively mobile so as to be able to adopt considerably different configurations in different environments. Based on a recognition of this feature of polymeric surfaces, a sequence of contact angle experiments is suggested to estimate: (a) the instantaneous as well as equilibrium surface energetic properties of a polymeric solid in an aqueous environment and (b) the time required for the polymeric surface to attain its equilibrium wetting characteristics in the aqueous environment. In order to illustrate the applicability of the suggested contact angle procedure, it is necessary to prepare model polymeric surfaces, which are smooth in surface texture, nonporous, and also chemically homogeneous. Such model surfaces were prepared in this study, by radio frequency sputter deposition of thin solid films of oxidized fluorocarbon compounds (from a Teflon FEP target) onto the smooth surfaces of highly polished, single crystal silicon substrates. The estimation of the wetting characteristics of the sputtered polymer films in an aqueous environment was then carried out by the suggested contact angle procedure. The results of the contact angle experiments indicate that the solid-water interfacial free energy of the sputtered polymer film which was initially equilibrated in an octane environment, decreases from an instantaneous value of 50.88 dyn/cm to an equilibrium value of 26.59 dyn/cm, over a duration of about 24 h. Such a change in the solid-water interfacial free energy of these model polymeric surfaces can arise due to a time-dependent reorientation of the buried polar groups of the solid from its bulk to its surface, when it is placed in contact with a strongly polar liquid like water. This interpretation was found to be consistent with the results of ESCA characterization, which indicated that the outer surface layers of the sputtered polymeric specimen contained a fair amount of the polar oxygen atoms that are capable of reorienting themselves from either the interior of the solid to its surface or vice versa, depending on their surrounding environment.

Adhesion is a surface phenomenon occurring in many processes, e.g., bonding, painting or varnishing. Knowing the adhesion properties is critical for evaluating the usability or behaviour of materials during these processes. Good adhesion properties favour the processes of bonding, resulting in high strength of adhesive joints. Adhesive bonded joints are used in many industries, and the subject of this study was 7075 aluminium alloy sheet bonded joints as typically used in the aviation or construction industry. Surface free energy (SFE) can be used to determine the adhesion properties of the materials. The SFE of the tested sheets was determined with the Owens–Wendt method, which consists in determining the dispersion and polar components of SFE. The purpose of this work was to correlate the bonded joint strength of selected aluminium alloy sheets to the surface free energy of the sheets that had been subjected to degreasing only and no other prior treatment was used. Single-lap bonded joints of 7075 aluminium alloy sheets were tested. Higher joint strength was measured for the thinner sheets, while the lowest strength was measured for the thickest sheets. This suggests that the thickness of the joined parts is an important factor in the strength of bonded joints. The comparison of adhesion properties to the strength of adhesive joints of tested materials shows that there is no direct relation between good adhesion properties (i.e., high SFE) and joint strength. As for degreasing, the highest joint strength was observed for aluminium alloy sheets with the lowest SFE; the sheets which were not degreased gave the highest SFE and highest joint strength.

Protective properties of zinc coating increase with an additional coating such as: chromate, phosphate, paint and polymer coating. Besides, additional treatment of zinc coating serves decorative purposes as well. The paper presents the influence of additional coating of zinc coating on their adhesive properties which are especially helpful in processes where adhesion plays an essential role. These processes include among others: gluing, painting or varnishing. Adhesive properties are characterized by the value of surface free energy.

Polyamide 6, polyamide 12, polybutyleneterephthalate, and polyetherimide films are plasma treated in an APGD unit using various applied voltages, gas flow rates, frequencies, and dwell times. The results show changes in the surface chemistry (FTIR); the degree of change in dynamic contact angle is found to be dependent on the polymer type, dwell time, and electrical characteristics of the plasma.

In order to characterize a solid surface, the commonly used approach is to measure the advancing and receding contact angles, i.e., the contact angle hysteresis. However, often an estimate of the average wettability of the solid–liquid system is required, which involves both the dry and wetted states of the surface. In this work, we measured advancing and receding contact angles on six polymer surfaces (polystyrene, poly(ethylene terephthalate), poly(methyl methacrylate), polycarbonate, unplasticized poly(vinyl chloride), and poly(tetrafluoroethylene)) with water, ethylene glycol and formamide using the sessile drop and captive bubble methods. We observed a general disagreement between these two methods in the advancing and receding contact angles values and the average contact angle determined separately by each method, although the contact angle hysteresis range mostly agreed. Surface mobility, swelling or liquid penetration might explain this behaviour. However, we found that the 'cross' averages of the advancing and receding angles coincided. This finding suggests that the cross-averaged angle might be a meaningful contact angle for polymer–liquid systems. Hence, we recommend using both the sessile drop and captive bubble methods.

After the impact of the great review of M. Strobel and C. S. Lyons on contact angle measurements, we discuss some claims of the authors. The Wilhelmy method is not generally “the best technique for measuring the contact angle hysteresis” as the authors claimed. Otherwise, we think that, even though equilibrium contact angle is an “unattainable” angle, the most-stable contact angle obtained from the system relaxation is experimentally accessible. The most-stable contact angle is energetically significant for evaluating quantitatively the surface energy value of rough, chemically homogeneous surfaces from the Wenzel equation, and the average surface energy of smooth, chemically heterogeneous surfaces from the Cassie equation. The most-stable contact angle, the advancing contact angle and the receding contact angles enable the thermodynamic description of the range of contact angle hysteresis and the distribution of metastable system configurations.