The main properties of corona discharges are reviewed, with emphasis on the features which make them unique for use as non-equilibrium chemical reactors : Their stability andease of operation over a wide range of gasesand pressures, including atmospheric : their sharply confined ionization regions where hot electrons interact with cold gas, inducing reactions without back reactions ; and their extended low field drift regions which act as gaseous electrolytes, inducing electrochemical reactions on surfaces. Present and future applications are discussed : Synthesis of ozone and ammonia, promotion of flames and combustion, surface treatment, and electrical insulation improvement.

A recent study has illustrated a sizeable increase in the printing characteristics of nonwovens following atmospheric plasma treatments. The improvement of properties such as wettability, printability and adhesion opens up new application prospects for treated fabrics.

The surface functionalization of polyimide (Matrimid^® 5218) films was carried out by cold plasma treatment with CF₄, N₂ and O₂ gases using a radio frequency discharge and the optimum plasma conditions were evaluated by water contact angle measurements. The surface hydrophobicity of polyimide films was obtained after CF₄ plasma treatment, while O₂ and N₂ plasma treatments contributed to the hydrophilic surface functionalization. X-ray photoelectron spectroscopy (XPS) results revealed the presence of CF_x, amino or oxygen-containing groups attached to the polyimide film surface depending on the treatment gas. A strong influence of the used plasma gas on the film roughness was determined by atomic force microscopy (AFM) measurements. The influence of the surface modification on CO₂, N₂ and O₂ gas permeation through the plasma treated films was evaluated. The permeation behaviour was characterized in terms of transport parameters, namely, coefficients of permeability, diffusion and solubility. The permeability coefficient of all plasma treated polyimide films for the studied gases (CO₂, N₂ and O₂) was found to decrease following the order of increasing the kinetic molecular diameter of the penetrant gas. Besides, the selectivity coefficient was found to be significantly increased after the plasma treatments – α_CO2/N2 was increased up to 36% and 98% for O₂ and N₂ plasma treated Matrimid^® 5218 films, respectively. The relationship between the gas permeation behaviour and the surface modification of polymer film by cold plasma was discussed.

In moist environments biaxially-oriented corona-treated polyethylene terephthalate (BOPET) film undergoes a decay in surface energy with time. This decay is a significant and well-known problem and it considerably restricts the industrial application of BOPET film. In the present study the decay effect and the dynamics of corona-treated BOPET film in an aqueous environment have been studied using water contact angle and variable angle X-ray photoelectron spectroscopy (XPS) measurements. In addition the surface decay mechanism of the corona-treated BOPET film in aqueous environments was analyzed and a molecular moving model for the decay mechanism is proposed.

BOPET corona films undergo a decrease in surface energy with time, a so called decaying effect, which has become a serious and widely known problem which prohibits their downstream industrial applications and needs to be carefully understood. Herein, the decaying behaviors and dynamics of decaying BOPET corona films in hot air were studied carefully by measuring water contact angle and surface tension and variable angle XPS. It was found that the molecular mechanism for the decaying effect involves migration of polar groups from the surface to the interior, and the decaying process is highly dependent on temperature. In addition, it was also found that such a temperature-dependent decay process is related to the glass transition of BOPET, and the glass transition temperature (Tg) can be predicted through analysis of the dynamics.

In this work, two different techniques to modify polymeric surfaces are compared: laser irradiation and ion implantation. The treated polymers were samples of ultra high molecular weight polyethylene. The irradiation treatment was performed by utilizing two different laser sources operating in the UV and IR range by applying many laser shots in an air atmosphere. Ion implantation was performed using a new laser ion source accelerator with an accelerating voltage of 40 kV. Contact angle, roughness and Fourier transform infra red measurements were carried out before and after the treatments in order to compare surface characteristics. An increase of the wettability and roughness was observed when using UV laser treatment, while an increase of the hardness was obtained by ion implantation.

Plasma chemistry of polymers may be categorized into two major types of reactions as (1) surface reaction of polymers and (2) polymerization of monomers by plasma. So far as these two types of reactions are concerned, plasma is very similar to other ionizing radiation, such as ..gamma.. radiation, x radiation, UV radiation, and high-energy electron beams, which can (1) initiate polymerization of certain monomers, and create free radicals on polymer exposed, which lead to (2) crosslinking of the polymer and/or (3) degradation of the polymer, or can be further utilized as the initiation sites of (4) graft copolymerization. The characteristic features of plasma are (1) the radiation effect is limited to the surface, and the depth of the layer affected by the plasma is much smaller than that by other more penetrating radiation, and (2) the intensity at the surface is generally stronger than that by the more penetrating radiations. Therefore, plasma treatment provides an ideal means of modifying surface properties of polymers. Examples are presented and discussed.

Drop-on-demand inkjet printing, familiar to most of us from small home and office printers, is taking an increasing role in printing for the broader commercial and industrial market. Inkjet printing has made serious inroads into the market for printing banners and signs of all sorts. Wide-format and super wide-format printing is now the norm and has, to an increasing degree, superseded analog printing as the method of choice for printing large format and point-of-purchase signage. Overall, inkjet printing has now taken over 30 percent of the general sign and banner market. One area of printing that holds promise for future growth is that of packaging and labels. Many forms of commercial printing, although a huge market today, are threatened on multiple fronts from various forms of electronic media. Printing and decoration for packaging, on the other hand, is expected to increase in volume in the foreseeable future. In spite of this great promise, penetration of digital printing, in general, and inkjet printing, in particular, into packaging and label printing is still in the low single digits. This article will focus on the label market as an example of printing for packaging. Printing for packaging is a much broader and diverse subject than just labels, but many of the conclusions that follow can be extrapolated to the broader packaging market. Toner-based methods, both wet and dry, have been at the vanguard of penetrating the label market. Today, inkjet is slowly gaining market share. Inkjet has great potential because there is more flexibility in the type and characteristics of fluids that can be applied from an inkjet head. While there are many possible explanations for the relatively low penetration of digital printing into this market, this article will concentrate on the technical challenges involved in reliably printing labels of acceptable quality with inkjet printing. Only now is the inkjet printing industry overcoming these challenges.

A review is presented on the surface preparation of polymers and composites using atmospheric pressure plasmas. This is a promising technique for replacing traditional methods of surface preparation by abrasion. With sufficient exposure to the plasma afterglow, polymer and composite surfaces are fully activated such that when bonded and cured with epoxy adhesives, they undergo 100% cohesive failure in the adhesive. Depending on the material, the lap shear strength and crack delamination resistance (GIC) can be increased several fold over that achieved by either solvent wiping or abrasion. In some cases, a plasma-responsive layer must be incorporated into the top resin layer of the composite to achieve maximum bond strength to the adhesive. Adhesion does not correlate well with water contact angle or surface roughness. Instead it correlates with the fraction of the polymer surface sites that are oxidized and converted into active functional groups, as determined by x-ray photoelectron spectroscopy and infrared spectroscopy.

The wetting of solids by liquids is connected to physical chemistry (wettability), to statistical physics (pinning of the contact line, wetting transitions, etc.), to long-range forces (van der Waals, double layers), and to fluid dynamics. The present review represents an attempt towards a unified picture with special emphasis on certain features of “dry spreading”: (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.

A method is described for measuring dynamic surface and interface tension. The technique is essentially a variation of the pendant drop method in which the drop is allowed to oscillate after sudden formation at the tip of a syringe. Immediately after the oscillation stops but before the drop detaches, there is an instant of rest. At this moment, the profile of the drop is obtained using high‐speed photography. The boundary tension is then calculated from the profile using established methods. The technique is demonstrated on systems consisting of aqueous solutions of sodium stearate or oleate on one hand and mineral oil or air on the other hand. Surface or interface tensions may be obtained within 0.25 to 5 s after surface formation.

A new method of quickly and precisely measuring the surface tension of liquids and solutions is described. Utilizing the fact that the size of the bubbles formed from a gas flowing out of a nozzle is dependent on the nozzle diameter and the surface tension of the liquid used, the surface tension of a liquid can be determined by simply counting the number of bubbles formed from a gas flowing out at a constant flow rate or by measuring the period of bubble formation. The expected accuracy of the method is below 0.1% of variance. An evident correlation between the period of bubble formation and the surface tension was shown with several kinds of liquids which differ in surface tension. Changes in surface tension with varied degree of neutralization were determined in an aqueous solution of polyacrylic acid (PAA), 20-30 points of measurement with an accuracy of about 0.1% could be easily obtained within one hour.

Knowledge of the surface free energy of solids is important to understanding a number of processes involving wetting and adhesion to solid surfaces. The measurement of surface free energy has been a subject of active interest for at least 50 years. Despite the importance of the problem to a variety of industries a universally accepted method or set of methods for determination of solid surface free energies has not been agreed upon. In this review article various methods that have been used for the calculation of surface free energies are discussed. The limitations and concerns for employment of each of these methods are furthermore highlighted. Of principal concern is the use of contact angles that meet the requirements to be Young’s contact angles and the mixing of quantities obtained by contact angle measurements with those obtained by IGC, as surface free energies obtained by IGC tend to be larger than those obtained from contact angle measurements. Calculated values from IGC data are presumably larger than those from contact angle data as IGC data are often collected at very low surface coverages.

Flame treatment was initially developed in the 1950s to improve the adhesion properties of polyolefin films. Flame treatment typically creates oxidized species on the surface of films, by the formation of hydroxyl, carboxyl and carbonyl functionalities. Treatment (oxidation) depth varies with the substrate type, as does the generation of low molecular weight oxidized material at the surface. Surface exposure to flame treatment directly modifies the electron distributions and densities of molecules, resulting in oxidation at the polymer surface up to several nanometers deep. This review aims to provide a summary of developments regarding flame treatment as a valuable technique for improving the surface properties of polymers. In particular, in the first part special focus is on the combustion process and the main process parameters of flame treatments. In the second part, effects due to flame activation processes on polymers are discussed from different points of view (chemical, physical, morphological). Although the flame treatment represents the oldest activation treatment, the optimization of process parameters and the changes in chemistry and morphology of the polymeric materials were investigated in detail only recently.

The above results are intended to be suggestive rather than definitive. Nevertheless, they strongly support the premise that a cross-fertilization of both concepts and experimental data from the apparently unrelated fields of Lewis acid-base chemistry and adhesion theory can lead to potentially valuable results for both fields, emphasizing again the value of using a generalized acid-base vocabulary in describing the phenomena of chemistry, whatever one's area of specialization.

Natural rubber thermoplastic elastomers (NRTPEs) made by dynamic vulcanization of natural rubber during its mixing with polypropylene were subjected to various halogenation surface treatments. Marked reduction in the coefficient of friction is possible depending on the chemical treatment employed, TPE composition and the presence of a lubricant. As a result of halogenation there is an increase in the microroughness and hardness of the NRTPE surface. These effects in part explain the large decrease in the friction coefficients since the contact area is decreased. Thus NRTPE can be employed in applications requiring low friction, such as certain types of seals. Another consequence of halogenation of NRTPE is the increase in its surface energy which in turn promotes adhesion to various polar substrates. Indeed it was determined that halogenation of NETPE is an effective way of priming the surface of these materials for adhesion to acrylic and other substrates. Ethylene Propylene Diene Monomer rubber-Polypropylene thermoplastic elastomers (EPTPEs) were used as a control in this study to assess how a low unsaturation EPDM-based TPE compares with the high unsaturation NRTPEs in different halogenation surface treatments.

World-class, fully automated manufacturing processes rely more and more on advanced, environmentally friendly surface treatment technologies. An innovative atmospheric pressure plasma technique allows inline rubber and plastic manufacturing processes to become fully automated with total process control. A thorough pretreatment must produce surfaces with reliable and repeatable characteristics to achieve optimal adhesive bonding, coating and printing results. In addition, pretreatment must be delivered in a cost-effective and safe manner. The new process uses the high effectiveness of plasma for microfine cleaning, high-surface activation and nanocoating. In most cases the plasma application takes the place of environmentally unfriendly and costly solvent cleaning or chemical adhesion promoters and primers.

Atomic-force microscopy was used to study structural chemical transformations on the surface of polyvinyl chloride films subjected to modification with compounds based on acrylic acid derivatives, with preliminary activation of the polymer surface with a corona discharge.

The use of gas and/or liquid-phase carbon dioxide (CO2) with atmospheric plasma discharge surface pretreatment technology can remove micron and submicron particulates and hydrocarbon-based contaminations on plastics and metals. The cleaning process is based upon the expansion of either liquid or gaseous carbon dioxide through an orifice. The paper provides an understanding of the basic removal mechanism and provides experimental evidence of remarkable adhesion improvements relative to a broad range of applications in electrical, medical, and automotive manufacturing communities.