Most polymers and inorganic materials have acidic or basic sites (or both) which can interact to enhance wettability, adsorption, charge-transfer, and adhesion. These interactions, termed “polar” in the past, are independent of dipole moments and occur only when one material has acid groups which can interact with basic groups of the other material. the presence of a third component (solvent, plasticizer, penetrant, etc.) can interfere with adsorption, charge-transfer, or adhesion if the third component has strong enough acid-base interactions with either or both components. Water, a weak acid and a weak base, tends to weaken adhesion of polymers to inorganic materials but not when these have strong acid-base interactions.

A quantitative approach to predicting the enthalpy ΔH^ab of acid-base interactions between polymers and inorganic surfaces is presented based on determining the E and C constants of Drago's correlation for polymers and inorganic surfaces. Preliminary E and C constants are presented for polymethylmethacrylate, for chlorinated polyvinylchloride, for silica surfaces and for iron oxide surfaces.

Advances in glow discharge excitation for sputtering and surface treatment are reviewed. Conditions for the production of the glow discharges either by using a DC supply with a cold cathode or using an RF supply capacitively coupled to an electrode are discussed. Examples are given of surface treatment processes at present under study including RF magnetron sputtering of silica, a-C film growth in hydrocarbon plasmas and plasma nitriding.

The main available theories for the dynamics of wetting are brieflysummarized and discussed in reference to experiments. In partial wetting,hydrodynamic and molecular theories are equivalently efficient, even if thephysical meaning of parameters is not so clear in the former ones. Incomplete wetting, hydrodynamic theories are the only ones valid at lowangles, but some care has to be taken in the interpretation of the “slip length” introduced to remove the divergence of thedissipation at the contact line. The situation is less favourable at themolecular scale, where the theoretical description is still at itsbeginning, due to the multiplicity of behaviours.

The surface modification and adhesive bonding of a unidirectional GFRP Nylon-6,6 thermoplastic composite has been investigated. Wettability studies of plasma-treated specimens showed a significant reduction in the advancing and receding contact angles in water, relative to untreated material. The most effective treatment used oxygen plasma. The increases in wettability observed were determined to be the result of (a) an increase in the concentration of oxygen- and nitrogen-containing functional groups on the surface of the polymer and, (b) removal of fluoropolymer contamination, the source of which was identified as the PTFE mould release agent. This was established by SSIMS analysis. The surface modification resulted in significantly improved adhesion between the composite and an applied toughened epoxy adhesive; a considerable increase in the Mode II critical strain energy release rate, G_IIc, was observed following plasma treatment. Specimens treated in an oxygen plasma showed the greatest improvement in G_IIc, failing cohesively at a value of 1.6 kJ·m⁻² after only 15 seconds exposure. Without plasma treatment the specimens failed in an adhesive mode at very low values of G_IIc. Adhesion was further optimised by moulding the GFRP Nylon-6,6 against steel plates instead of PTFE.

Long-term durability of a structural adhesive joint is an important requirement, because it has to be able to support the required design loads, under service conditions, for the planed lifetime of the structure. One way of improving bond durability is through the use of surface treatments prior to bonding, which will activate the adherends’ surface, making it more receptive to the adhesive. In this study, the effects of two surface pre-treatments (corona discharge and flame ionization) on three timbers (maritime pine, iroko, and European oak) were evaluated quantitatively through contact angle measurements. These measurements allowed the determination of the changes in the timber surface thermodynamic characteristics, thus indicating which pre-treatment performed better. The results showed that both techniques increased each timber's surface free energy, which could translate into a durability enhancement of bonded joints. Overall, the corona-discharge treatment looks more promising, since this treatment leads to a bigger increase in the timber's surface energy, especially in its polar component, whilst also tended to be less species specific, less susceptible to variation, and the treatment effects lasted longer for this type of treatment.

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.

An atmospheric pressure plasma system has been used to treat amorphous polyethylene terephthalate (APET) to enhance its healseal properties to a polyethylene terephthalate (PET) film. The plasma treated APET sheet material was thermoformed into trays for use in the food packaging industry and heatsealed to a PET film. The heatsealing properties of the resulting package were assessed using the burst test technique. It was found that the plasma treatment significantly enhanced the adhesive properties and an increase in burst pressure from 18 to 35 kPa was observed for plasma treated food trays. The APET surface chemistry was assessed after plasma treatment where it was found that the plasma treatment had affected an increase in oxygen and an addition of nitrogen species to the polymer surface. The surface roughness (R_a) of the plasma treated samples was also observed to increase from 0.4 to 0.9 nm after plasma treatment.

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.

An ultraviolet-ozone oxidation process is shown to be an effective adhesion pretreatment for polyethylene (PE) and polyetheretherketone (PEEK). The data obtained indicate that the treatment gives considerable oxidation and improved wettability for PE and PEEK surface types. Treated surfaces were analysed using X-ray photoelectron spectroscopy (XPS) and water contact angles. XPS was also used to follow the chemistry and mechanism of the oxidation. Adhesion with a two-part epoxy was measured for PE and PEEK and was observed to improve significantly after pretreatment.