Thin plasma polymerized layers of acrylic acid (PPAA) were deposited onto polyethylene and muscovite mica surfaces. Structure and surface properties of the deposited layer depend on the polymerization conditions. The content of carboxylic groups in the layer decreases, whereas the degree of crosslinking or branching increases, with increasing discharge power. A soft, sticky layer with a low contact angle against water is obtained when a low discharge power (5 W) is used. In contrast, a hard film with a rather high water contact angle is obtained when the discharge power is high (50 W). A surface force apparatus was employed to study some film properties including adhesion force, crack formation, and capillary condensation. The adhesion force between plasma polymerized acrylic acid layers prepared at a low discharge power is high in dry air. It decreases remarkably in humid air and no adhesion is observed in water. In dry air, the adhesion force between PPAA layers decreases as the discharge power increases.

The wetting of cylindrical monofilaments by liquid polymers is a problem of much scientific and technological importance. In particular, the characterization of the physicochemical nature of interfaces is a key problem in the field of advanced fibrous composites. The macroscopic regime contact angle, which reflects the energetics of wetting at the solid-liquid interface, is difficult to measure by usual methods in the case of very thin cylindrical fibers.

In the present article a numerical method is proposed for the calculation of macroscopic regime contact angles from the shape of a liquid droplet spread onto a cylindrical monofilament. This method, which builds on earlier theoretical treatments by Yamaki and Katayama [1], and Carroll [2], very much improve the accuracy of the contact angle obtained. Experimental results with high-strength carbon, para-aramid, and glass fibers, are presented to demonstrate the high degree of accuracy of the method proposed.

The surface modification of isotactic polypropylene (PP) in a microwave plasma of CO2 is described. The modified PP is characterized in bulk and also at its surface. The mechanism of plasma modification is discussed in terms of degradation and oxidation. The degradation leads to volatile products and to the formation of a layer of oxidized oligomers of PP. The oxidation leads to ketone, acid or ester groups. The degradation and oxidation rates depend on plasma parameters (duration, discharge power, gas flow, pressure, discharge or post-discharge treatment). The oxidation rates vs the various plasma parameters show a maximum. The crosslinking of PP (Crosslinking Activated Species of INert Gases) seems to be negligible.

Despite the recognition of several sources of variation of contact angle, both between and within sessile drops on plane substrates, no comment has ever been made on the statistical treatment of observed angles, especially those around single drops. Circumperipheral observations are suggested as essential, and analysis using cos theta in an autocorrelation model is proposed as a general means of handling such data.

Polyethylene (PE) and polypropylene (PP) were oxygen plasma treated and aged in carefully reproducible conditions. The effect of aging on the surface chemistry, wettability and adhesion were studied using a combination of techniques: contact angle measurements, XPS, SSIMS, adhesion tests (shear and pull).

PE was found to be relatively insensitive to aging both in terms of wettability and adhesion, due to crosslinking during plasma treatment, which is likely to reduce macromolecular mobility within the surface layer.

In the case of PP, dramatic decreases of wettability occur with time, due to macromolecular motions leading to minimization of oxygen-containing functions at the surface. This behavior was shown to affect the adhesion performance of treated PP.

PTFE was treated with oxygen and argon plasmas and the effects of treatment were evaluated by actinometry, SEM, XPS, static SIMS and contact angle measurements. At short treatment times for both plasmas and at long treatment times for argon plasmas, chemical modification of the surface was dominant, while at longer oxygen plasma treatment times, surfaces are deeply etched but chemically equivalent to untreated PTFE. Interestingly, the change in surface chemistry is paralleled by a simultaneous variation in plasma chemistry, suggesting that the two vary accordingly. The wetting behaviour of treated surfaces is interopreted on the basis of current theories on surface dynamics and contact angle hysteresis.

Oxygen plasma-treated polydimethylsiloxane surfaces were aged in a low-energy (air) and in a high-energy (water) medium. Treated samples were characterized using a combination of surface-sensitive techniques: X-ray photoelectron spectroscopy, static secondary ion mass spectroscopy, and contact angle measurements. Plasma treatments cause large increases in surface tension of treated samples. When aged in air (low-surface-energy medium) the samples returned to a low-surface-tension situation. The mechanism was a combination of diffusive burial of polar groups in the bulk and condensation of silanol groups formed by plasma treatment and consequent crosslinking. When aging was performed in water, a high surface tension was maintained.

Corona discharge (CD) treated polyethylene films were examined using X-ray photoelectron spectroscopy (XPS) and a variety of chemical derivatization techniques. The composition of the CD-treated surfaces were found to be relatively unaffected by aging at temperatures between 70 and 80°F. Ink adhesion testing of films treated under progressively more serve conditions indicated the efficiency of adhesion varied directly with the severity of treatment. Derivatization of CDtreated polyethylene films with pentaflurophenylhydrazine (PFPH) resulted in the formation of a stable hydrazone complex. The PFPH complex extends the detection limit for enolizable carbonyl groups ca. eight-fold and provides relative quantitation of the number of these groups on variously treated polyethylenes. Formation of the hydrazone complex destroyed ink adhesion, indicating that the complex had blocked the site responsible for chemical bonding to the ink. Adhesion of water-soluble printing inks to CD-treated polyethylene is a direct consequence of hydrogen bonding between enolic hydroxyls on the polymer surface and carbonyl groups of the ink.

Macroscopic wetting behavior is investigated theoretically from a thermodynamic viewpoint. The axisymmetric liquid meniscus formed under a conical solid surface is chosen as the subject of the theoretical analysis. Using the meniscus configuration obtained by the Laplace equation, the total free energy of the system is calculated. In the case of the half vertical angle of the cone φ = 90 deg (horizontal plate), the system shows thermodynamic instability when the meniscus attaches to the solid surface at the contact angle. This result, unlike the conventional view, agrees well with the practical wetting behavior observed in this study. On the other hand, when 0 deg < φ < 90 deg, the system shows thermodynamic stability at the contact angle. However, when the solid cone is held at a position higher than the critical height from a stationary liquid surface, the system becomes unstable. It is possible to measure the contact angle easily using this unstable phenomenon.

Using the literature data of the refractive index, the structural unit molar volume of polymers and their dipole moment, as well as the literature data of the polarizability, ionization potential, and dipole moment of many liquids, values of the Φ parameter for paraffin—liquid and polymer—liquid interfaces were calculated. Next, introducing these values of Φ and the earlier measured values of the contact angle for many liquids to the Young equation, values of the surface free energy (γ_S) of paraffin, polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene terephthalate (PET), and polymethacrylate (PMMA), were determined. It was found that the average values of γ_S for these solids were in agreement with those calculated on the basis of geometric, harmonic, or harmonic—geometric mean approaches. The values of the surface free energy of paraffin, PTFE, PE, PET, and PMMA were also calculated from the Young equation modified by Neumann et al. and, using the earlier measured values of the contact angle for many liquids, they were compared with the values obtained by other methods. Next, employing the mean value of the surface free energy, values of the contact angles for many liquids were calculated and compared with those measured earlier for the same liquids. It was found that for paraffin, PTFE, and PE there were big differences among the values of their surface free energies calculated from the contact angles for some liquids; however, the average values were in agreement with those obtained by other methods. The average values of the surface free energies of PET and PMMA were also in the range of the results obtained by other authors. It was also found that the average deviations of the contact angles calculated from the Young equation modified by Neumann et al. from the measured ones were slightly larger than those of the contact angles calculated from equations employing the geometric and harmonic means of the surface free energy components; the method of Neumann et al. may also be used to predict the wettability in some systems.

To draw a relationship between surface concentration of the siloxane segment and adhesion performance, surface properties of the polydimethylsiloxane—poly(methyl methacrylate) block copolymers(PDMS-b-PMMA) prepared via poly(azo-containing siloxaneamide)s and their PMMA blends have been studied by measurements of FT-IR spectra, water contact angle, ESCA spectra and 180° peel strength toward pressure-sensitive adhesive tape. The water contact angles of the chloroform-cast blend films increased abruptly with siloxane bulk concentrations, or siloxane contents, particularly, on the air-side surfaces to reach almost 100° in low siloxane content. A marked increase of the contact angle was observed in the blends containing siloxane chain length (SCL) of longer than 2000. ESCA data evidently confirmed for these blend systems that the siloxane segments with low surface energy were accumulated or enriched mainly on the air-side surface, and that, on the other hand, polar PMMA segments with high surface energy were oriented to the glass-side surface and the inside of the films. This surface accumulation behavior of the siloxane segments reflected the 180° peel strength, as a measure of adhesion performance. The water contact angle and 180° peel strength were unequivocally correlated to the siloxane surface concentration estimated from ESCA data. Conversely, in the compression-molded blend films made by a hydraulic press between a Teflon and a stainless steel plate, the extent of surface accumulation of the PDMS segment was lower than that of the chloroform-cast films, suggesting lower degree of segment migration in hot-press films, probably due to substrate surface energy and lower relaxation in the blend melts.

Polymers formed from plasma-polymerized methane were employed to modify the surface properties of silicone rubber membrane. Polymers were evaluated based on the energy input parameter W/FM, where W is the discharge power, F is the monomer flow rate, and M is the molecular weight of the monomer. Dealing with the characteristics of plasma polymerization and the deposited polymer film, the effect of pumping rate on deposition rate and the coating thickness, surface energy, and gas permeabilities of methane-plasma-polymer-coated silicone rubber membrane were investigated in three plasma regions. Because more reactive species are expelled at high pumping rates, the monomer-deficient region is reached at lower W/FM in the high pumping rate system than that in the low pumping rate system. The composite parameter W/FM had a strong influence on coating thickness, gas permeability, surface energy, and the polar component of the surface energy but little effect on its dispersion component. Examination of gas permeabilities indicated that coating thickness was another important controlling factor on the properties of plasma polymer.

New reaction products have been generated on polyethylene and polystyrene surfaces using a novel two-step process. The first stage involves exposure to a downstream nitrogen plasma, and the second to either ozone or a corona discharge. It is observed that each of the two-step reactions yields very different reaction products, with an apparent increase in the formation of CO functional groups in the former case and the formation of surface NO₂ groups in the latter case.

The effect of a remote nitrogen plasma on polyethylene and polystyrene was studied. The gas flow rate, the dilution of reactant gas, exposure times, and reactor base pressure were all found to have a large impact on the efficiency of nitrogen incorporation. Optimum conditions caused 18 atom % nitrogen to be incorporated within 20 seconds for polyethylene and 10 seconds for polystyrene. Studying a remote nitrogen plasma treated polyethylene sample over a period of 1 month indicated that except for a drop in the % N on initial exposure to air the concentration of nitrogen on the surface remained steady within the experimental limits. Angle resolved photoelectron spectroscopy indicated that nitrogen is incorporated to a depth below the analysis depth of XPS.

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.

The polypropylene films are pretreated in a nitrogen or ammonia low-pressure plasma in order to improve their adhesive properties towards an in-situ deposited aluminium coating. The treatment conditions are similar to industrial ones and treatment times as short as 23 ms allow a considerable improvement of the adhesion between the polypropylene and the aluminium. The aim of this work is to understand better the mechanisms involved in the adhesive phenomena. Indeed, the modifications created by the plasma (for very short treatment times) are not easily detected. SSIMS has revealed the presence of a thin non-homogeneous film of light-weight hydrocarbons on the non-pretreated polymer. This film is responsible for the non-adhesion of the aluminium coating onto the polymer. Actually when this film is removed by a cleaning process induced by the plasma, the interactions between the aluminium and the polypropylene are strong enough to allow a good adhesion. This explains one of the effects of the plasma and more experiments will be carried out in order to determine the key factor of the phenomenon: the role of the oxygen at the interface on the treated polymer will be investigated as well as the diffusion depth of the treating gas.

XPS and contact angle measurement have been used to study oxygen–plasma-treated polypropylene (PP) surfaces aged at variable temperatures. Surface rearrangement leading to low wettabillity has been observed, without alteration of the surface composition, as determined by XPS. Experimental results have been interpreted in terms of internal rearrangements of a modified layer, <5 nm thick, formed on top of the PP and immiscible with it.

We also modelled the composition of the surface layer and calculated the relative mobility of modified and non-modified polymer chains. On this basis, the experimentally observed behaviour can be interpreted in terms of surface rearrangement driven by a compromise between striving for lower surface tension and maximizing inter-and intramolecular interactions, mainly hydrogen bonds.

The surface composition observed after treatment with plasma, corona, flame or other for enhancing surface tension is then time dependent. For this reason, the procedure used for surface analysis, namely the time allowed for surface equilibration, should be specified in reports.

Several commercial polymers (polyethylene, polyimide, polytetrafluoroethylene, polyvinylchloride and polycarbonate) have been treated by low temperature glow discharge plasmas in various gases, namely NH3, O2, Ar, and CF4. These surface modifications were performed in "pure" microwave (2.45 GHz, "single-mode") or in combined microwave/radio frequency (2.45 GHz/13.56 MHz, "dual-frequency") plasma. Important systematic changes of the surface composition, wettability, and adhesion of thin metal films were observed for different substrate bias values, and for the different gases. The modified surface-chemical structure is correlated with contact angle hysteresis of water drops; this helps to identify which surface characteristics are connected with the wettability heterogeneity and with adhesive bonding properties, and how they are influenced by plasma-surface interactions.

Low-pressure plasma treatment has been introduced for the practical pretreatment of automobile bumpers. The differences between the conventional solvent vapor pretreatment and low-pressure plasma or corona treatment, are shown schematically.

The surface free energy of polyacrylonitrile carbon fibers was investigated by using the Wilhelmy technique. The difference in surface free energy between immersion and emersion was observed for the carbon fiber pyrolyzed at 2500 °C.

In contrast, the hysteresis disappeared with repyrolyzation of the carbon fibers at 3000 °C. Auger electron spectroscopic analysis indicated that the surface of the latter carbon fiber (repyrolyzed at 3000 °C) consisted of the basal planes of graphite. Rough surface topography of the carbon fiber repyrolyzed at 3000 °C, as observed by scanning electron microscope, did not affect the hysteresis. Therefore, the contact angle hysteresis was attributed to the chemical adsorbants on the activation sites of the fiber surfaces, as detected by Auger electron spectroscopy.

In a previous paper it was shown that negative interfacial tensions between predominantly monopolar surfaces (i.e., surfaces with mainly H-acceptor properties) and polar liquids are real phenomena. Such negative interfacial tensions do however decay rapidly. For miscible liquids, the decay of the interface is, in general, so rapid that it practically excludes measurement of interfacial tension. However, if one liquid is present in the form of a gel, and if the other liquid is placed as a drop upon the gel, there is often enough time to measure contact angles. This may be done at various concentrations of the liquid encased in the gel, and an extrapolation made to zero concentration of the gelling agent. With this method we found the existence of negative interfacial tensions at liquid/liquid interfaces.

A process for surface modification of oriented polymeric film is disclosed. The process, applicable to polyesters, polyolefins, and polyamides, involves subjecting the film surface to at least one short pulse of intense electromagnetic radiation. Such surface treatment enhances the heat seal adhesion of the oriented polymeric film.