The process of modifying the surface of polytetrafluoroethylene in a glow discharge plasma in vapors of organic compounds of various classes was investigated. It was established that the greatest increase of wettability is seen when modification is done in acrylic acid vapor. Multiple attenuated total internal reflection infrared spectroscopy was used to study the spectra of the coatings that formed and to demonstrate their difference in the case of acrylic acid.

Polymers have wide-ranging applications in food packaging and decorative products, and as insulation for electronic devices. For these applications, the adhesion of materials deposited onto polymer substrates is of primary importance. Not all polymer surfaces possess the required physical and/or chemical properties for good adhesion. Plasma treatment is one means of modifying polymer surfaces to improve adhesion while maintaining the desirable properties of the bulk material. This paper addresses the interaction of organic surfaces with the various components of a plasma, with examples taken from a review of the pertinent literature.

A new plasma-based micropatterning technique, here referred to as plasma printing, combines the well known advantages given by the nonequilibrium character of a dielectric barrier discharge (DBD) and its operation inside small gas volumes with dimension between tens and hundreds of micrometres. The discharge is run at atmospheric pressure and can be easily implemented for patterned surface treatment with applications in biotechnology and microtechnology. In this work the local modification of dielectric substrates, e.g. polymeric films, is addressed with respect to coating and chemical functionalisation, immobilisation of biomolecules and area-selective electroless plating.

Atmospheric pressure plasma treatment has unique advantages over vacuum treatment for such industrial applications as surface energy ehancement of materials, cleaning, decontamination, and sterilization of surfaces, surface etching, plasma chemical vapor deposition (PCVD), and related tasks. The MOD VIII plasma reactor system has been developed to provide roll-to-roll surface treatment of fabrics and films using a One Atmosphere Uniform Glow Discharge Plasma (OAUGDP®) operating in air. Webs can be continuously and uniformly treated by proper control of gas flow; electrode configuration; plasma voltage, current, and frequency; fabric speed; and fabric tension.

A novel plasma chemical process PPCP (pulse corona induced plasma chemical process) can produce copious active radicals in air under NTP (normal temperature and pressure) by using an extremely fast rising narrow high voltage pulse between corona electrodes and grounded counter electrodes so that intense streamer coronas are generated. This provides an effective means of surface treatment to a plastic material placed between the two electrodes through generation of free bonds on the surface directed to the corona electrodes. Special features of this method are that it can cope with a complex shape of the material to be treated, and that it does not spark even at the periphery near the grounded counter electrode. This method is suitable for the surface treatment of polypropylene bumpers so as to provide a strong adhesion of color paint to it. The adhesion strength of a paint film is raised from zero to ca. 1000 g/cm/sup 2/ by PPCP treatment for 60 seconds.

Various aspects of corona discharge treatment are reviewed. Particular attention is given to the Lissajous power measurement procedure; the significance of quartz, ceramic, or rubber as the dielectric in corona treaters; watt density considerations; and stabilizers and fatty acids.

Surface charge decay on thick flat samples of high temperature vulcanized silicone rubber is studied prior and after ac and dc corona pre-treatments. It is found that the charge decay rate on the material exposed to ac corona becomes much higher and sensitive to moisture content in the surrounding air. These features are associated with an increased surface conductivity and formation of a silica-like layer on the polymeric surface, both resulting from ac corona treatment. In contrast, characteristics of the charge decay on the material exposed to dc corona are found to be similar to that measured on untreated samples.

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.

Applications of corona discharge induced plasmas and unipolar ions are reviewed. Corona process applications emphasize one of two aspects of the discharge: the ions produced or the energetic electrons producing the plasma. The ion identities depend on the polarity of the discharge and the characteristics of the gas mixture, specifically on the electron attaching species. The electron energies depend on the gas characteristics and on the method of generating the corona. In general, in an application using ions, the corona induced plasma zone will occupy a small fraction of the total process volume, while a process using the electrons will fill most of the volume with the plasma. Current state-of-the knowledge of ionized environments and the function of corona discharge processes are discussed in detail.

A low-temperature, atmospheric pressure oxygen and helium plasma was used to treat the surfaces of polyetheretherketone, polyphenylsulfone, polyethersulfone, and polysulfone. These aromatic polymers were exposed to the afterglow of the plasma, which contained oxygen atoms, and to a lesser extent metastable oxygen (^1δ_g O₂) and ozone. After less than 2.5 seconds treatment, the polymers were converted from a hydrophobic state with a water contact angle of 85±5 to a hydrophilic state with a water contact angle of 13±5 . It was found that plasma activation increased the bond strength to adhesives by as much as 4 times. X-ray photoelectron spectroscopy revealed that between 7% and 27% of the aromatic carbon atoms on the polymer surfaces was oxidized and converted into aldehyde and carboxylic acid groups. Analysis of polyethersulfone by internal reflection infrared spectroscopy showed that a fraction of the aromatic carbon atoms were transformed into C=C double bonds, ketones, and carboxylic acids after plasma exposure. It was concluded that the oxygen atoms generated by the atmospheric pressure plasma insert into the double bonds on the aromatic rings, forming a 3-member epoxy ring, which subsequently undergoes ring opening and oxidation to yield an aldehyde and a carboxylic acid group.

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.

A low-temperature, nonequilibrium plasmajet process for activation of polymer surfaces has been developed. A stream of oxygen is partially dissociated by a glow discharge, expanded to high velocity through an orifice into a region of lower pressure, and impinged on the desired surface. Parameters measured before and after treatment of a variety of polymers include weight, surface-bonding characteristics, and wettability. The weight loss of the polymer increases with exposure time, discharge power, and proximity to the atom source; its relation to the changes in surface properties is discussed.

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.

A dielectric barrier discharge in a corona process configuration is used to treat the surface of fluoropolymers in a nitrogen–organic precursor environment. The surface chemistry, thickness, and water contact angle of the deposited coatings are measured and used to build up an output matrix to be correlated with an input matrix built using electrical parameters of the discharge, the gas mixture chemical composition, and spectroscopic parameters measured in both the infrared and ultraviolet–visible emission spectral regions. A partial least-squares regression (PLSR) model enables determining the most important plasma parameters to drive the coating physicochemical characteristics. From the PLSR model, it is determined that the plasma electrical parameters drive the surface modification process, at the expense of other plasma characteristics such as gas flow, gaseous precursor concentration, nitrogen vibrational temperature, and the level of gaseous precursor conversion within the plasma.

Equations based on a simple model of surfaces and interfaces have been found useful for relating quantitatively several previously unrelated fields of surface chemistry {10-13). These equations introduce a new term — the London dispersion force contribution to the surface free energy (7d)—and make use of this term for the accurate calculations of surface tension, interfacial tension, contact angles, heats and free energies of immersion, heats and free energies of adsorption, and the long-range van der Waals attractive forces. The accuracy of predictions of values verifiable by experiment lead one to expect that predictions of un-verifiable quantities, such as the magnitude of attractive forces at solid-solid interfaces, are to be trusted. This approach should appeal especially to those who need to use the results of surface chemistry and would prefer to calculate from existing values rather than make new experimental determinations. It should also appeal to those teaching surface chemistry in that it relates for the first time several widely separated fields of surface chemistry. Most noteworthy is the ability to calculate heats and free energies of adsorption of gases on solid surfaces directly from measurements of surface tensions and contact angles. The calculation of the long range van der Waals attractive constant, A, from values of 7d is also very attractive.

A STUDY has been made of the densities, the surface tensions and their temperature coefficients, the interfacial tensions against water, the spreading pressures, and the force-area and potential-area relations of monolayers on water of various types of linear polyorganosiloxanes. The McLeod constants and parachors have been calculated, and their application to the type analysis of the silicones is discussed. Relations have been found between the critical spreading pressure, the spreading coefficient, and the viscosity. A study of the force-area curves revealed that the polymethylsiloxanes and the related polymers containing a small proportion of phenyl substituents are able to coil reversibly into helices made up of about six monomers per turn. Conclusions relative to the molecular structures in thin films have been carried over to the three-dimensional liquid state.

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.