Surface composition, fluorine distribution, and morphology were determined for polyimide films modified downstream from microwave plasmas containing CF₄/O₂. Complementary analytical techniques including x‐ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, and scanning electron microscopy yielded a more complete understanding of polyimide fluorination and subsequent etching of the modified film. Depth of fluorination increased nonlinearly with treatment time for films exposed downstream from a CF₄‐rich plasma. Exposure downstream from an O₂‐rich plasma resulted in a reduction of thickness in both the fluorinated layer and the unmodified polyimide during etching. Finally, a model for fluorination of polyimide and subsequent removal is proposed.

Microbial colonisation of synthetic plastic films is normally slow, which affects the total period of biodegradation. Correlation between the modified surface condition and the ability for microorganisms to colonise low-density polyethylene (LDPE) film was studied. Corona discharge treatment was applied to obtain enriched and activated surface condition of LDPE film. It was found from water contact angle and FTIR spectrum evaluations that surface energy was significantly increased due to production of free radicals. Stabilised oxidised LDPE surface was also obtained by further exposure to the corona which gave more suitable condition for subsequent colonisation. Results were compared with UV irradiated (photo-oxidised) LDPE films. Colonisation of corona discharged and UV treated LDPE films were tested in the laboratory environment using known fungal isolates and in a natural compost environment. More active microbial colonisation was observed in all cases for corona discharged and UV treated LDPE films. Far longer UV exposure was required to have the same physicochemical and biological effect as the corona discharge treatment.

The present volume and its companion Volume 1 document the proceedings of the Symposium on Surface Contamination: Its Genesis, Detection and Control held in Washington, D.C., September 10-13, 1978. This Symposium was a part of the 4th International Symposium on Contamination Control held under the auspices of the International Committee of Contamination Control Societies, and the Institute of Environmental Sciences

The dispersion force component of surface free energy, γ, and the nondispersive interaction free energy between solid and water, I, were determined by the two-liquid contact-angle method, i.e., by the measurement of contact angles of water drops on plain solids in hydrocarbon, for commercialy available organic polymers such as nylons, halogenated vinyl polymers, polyesters, etc. A method to estimate the I values from the knowledge of the polymer composition is also proposed, on the basis of the assumption of the spherical monomer unit and the sum of interactions between functional groups and water molecules at the surface.

The London dispersive component of surface free energy γ_s^d and the nondispersive interactions with polar liquids W I_swⁿ were determined for hydrophilic polymers S, that is, cellulose, poly(vinyl alcohol) (PVA), and poly(methylmethacrylate) (PMMA). On applying the geometric-mean relation $\text{2(γ}{}_{\mathrm{s}}{}^{\mathrm{d}}\text{γ}{}_{\mathrm{w}}{}^{\mathrm{d}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ to the dispersive interaction with W I_sw^d, the γ_s^d values were found to be 30, 29, and 37 erg·cm⁻² for cellulose, PVA, and PMMA, respectively. Each of them is completely independent of the nature of the testing liquids W, indicating that the geometric-mean equation is appropriate for representing the dispersive interaction. On the contrary, such a geometricmean expression is shown to be inapplicable to the nondispersive interactions. It is suggested that Fowkes' approach, in which intermolecular forces are regarded to be dominated by dispersion force interactions and electron donor-acceptor interactions, is more reasonable than the popular approach.

A semicontinuous, if capacitively coupled plasma polymerization apparatus was designed and constructed to coat the internal surface of a small-diameter plastic tubing. The glow zone was restricted to a small area to obtain a uniform coating of plasma polymer over the entire length of tubing (13 m long). It was found that a uniform coating can be achieved by maintaining the glow discharge parameters and velocity of moving substrate. In such a reactor, it was found that the deposition rates obtained for plasma polymers of tetrafluoroethylene, hexafluoroethane, and hexafluoroethane/hydrogen were very high compared with those polymerized in a conventional plasma polymerization apparatus. Special attention was needed to avoid deposition of an excessively thick coating, which was found to damage the barrier characteristics of the coating

The effect of time and surface contact on corona treated material can be measured and evaluated. Both components cause degradation of dyne level readings of wettability. However, the most significant cause, though it can be isolated, cannot be completely eliminated. A solution to the problem is possible but requires cooperation between material producers and converters.

Surface free energy (SFE) is a property which depends on the chemical state and roughness of the surface and it is necessary to develop a reliable method to evaluate SFE value on a small area, taking into account these two different contributions. Today contact angle methods are the most used and they allow to evaluate the global mean value of SFE on areas of mm² size. With these methods, it is not possible to evaluate the effects of roughness, surface defects, chemical contamination on SFE value. In addition, it is difficult to determine the surface free energy value on small components which have dimensions smaller than drop diameter. Nanoindentation and atomic force microscopy techniques provide alternative direct measurement methods to evaluate the SFE on small areas (on the order of μm² or nm²) through a contact mechanism triggered by the contact of two bodies. In order to evaluate the adhesion properties, currently three models, Johnson– Kendall–Roberts, Maugis–Dugdale and Derjaguin–Muller–Toporov, use the value of pull-off force (force required to separate the indenter tip from the sample). All influences of surface morphology on SFE values are lost using these methods. In fact the adhesion value obtained refers to the energy balance between two conformal surfaces, which depends mainly on the morphology of the harder material (i.e., diamond tip). In this work we describe a new methodology for the SFE determination consisting in the modeling and quantitative evaluation of the interaction between the tip and sample surface during the approach phase in a nanoindentation test. During the test, the nanoindenter tip is attracted to the sample surface until the sample reaction forces become significant (in this case physical contact between two bodies is achieved). The SFE value is evaluated using experimental force of attraction and displacement of the nanoindenter spherical tip when it approaches the sample surface. In this method the sample surface is not altered by the tip, therefore unlike pull-off force method, it could be very useful to evaluate the actual SFE considering the effect of sample morphology (controlled roughness or pattern).

This invention relates to treatment of organic thermoplastic polyme-ric surfaces to render the surfaces more wetta'ble by water and/or other liquids, more printable and dyeable and, in general, more adherable.

The Lewis acid-Lewis base properties of various polymers have been determined by measuring the contributions γ_s ⁺ and γ_S ^- to the solid surface free energy using the contact angle approach of van Oss, Chaudhury, and Good. A new linear method to solve for γ_S ⁺ and γ_S ^- is employed in addition to the usual approach which uses three simultaneous equations. The set of liquid surface tension parameters developed by van Oss, Chaudhury, and Good, and the recent set of values developed by Della Volpe and Siboni are both useful in distinguishing between acidic and basic polymers. The adhesion (peel force) of an acidic pressure-sensitive adhesive is greatest on a basic oxide film. In addition, the adhesion (pull-off force) of the basic polymer poly(methyl methacrylate) is greatest for acidic oxide films. Thus, direct experimental evidence is provided as to the importance of Lewis acid-Lewis base effects in the adhesion of polymers on oxide-covered metals.

A droplet of liquid placed on a flat high-energy solid surface spreads to give a thin film so that no macroscopic droplet shape exists. On a chemically identical solid surface with only the geometry changed to a cylinder, the same droplet can have an equilibrium conformation. When the equilibrium conformation is of a barrel type, the profile of the droplet changes rapidly in curvature as the three-phase contact line is approached and the direct measurement of the contact angle is difficult. This work considers the theoretical profile for barrel-type droplets on cylinders and discusses how the inflection angle in the profile depends on droplet parameters. Experimental results are reported for poly(dimethylsiloxane) oils on a range of fiber surfaces and these are used to estimate the equilibrium contact angle from the inflection angle. The drop radius and volume dependence of the inflection angle is confirmed.

The surface modification of high density polyethylene by a CO₂ microwave plasma is described with the aim of fixing carboxylic groups. The characterization is discussed in terms of functionalization, degradation, crystallization and cross-linking. The formation of carboxylic acids seems mainly favored by the presence of the CO₂ active species. The degradation leading via chain scissions to the formation of volatile byproducts is shown to be heterogeneous by mainly affecting amorphous zones. The structural modification is associated with a twisting motion of macromolecular chains having defects to more organized conformations. Finally, cross-linking appears weak due to the absence of chromophoric sites and of VUV radiations in the plasma.

Polydimethylsiloxane (PDMS) materials show the unique phenomenon that when exposed to electrical discharge, such as corona discharge, their hydrophobic surface becomes hydrophilic. However, after a certain relaxation time they gradually regain their hydrophobicity. In this study the adhesive force obtained by AFM force distance measurements using a hydrophilic Si3N4 probe is used to track the recovery of the hydrophobicity. The time constant of the recovery can be determined by measuring the adhesive force as a function of the recovery time after corona exposure. It is shown how these time constants can be used to monitor the recovery rate as a function of corona treatment time for both filled and unfilled PDMS compounds.

The treatment of surfaces by corona discharges is a well-established method to improve surface properties. The surface to be treated is moved continuously and is exposed to transient gas discharges, known as microdischarges, in air at atmospheric pressure between electrodes, where at least one electrode is covered with a dielectric barrier. Because of the short duration, only some 10 ns, the current through the microdischarges is predominantly carried by electrons. The ion temperature remains close to room temperature. Owing to these properties such discharges are qualified to treat surfaces which are sensitive to higher temperatures. For a large number of applications this treatment is adequate, but the adhesion of aqueous glues and inks to some plastic materials is insufficient if the surfaces are treated in this way. Furthermore, it is difficult to meet the requirements of surface properties of, for instance, polyolefine film (e.g. surface tension, adhesion). This material is not based on monomers containing chlorine or fluorine and is preferred for ecological reasons. This paper presents the results of experiments which demonstrate that in comparison to a common corona treatment significant improvements in surface properties of plastic materials can be achieved if repetitively generated pulse trains and reactive gases are used instead of air. If, for instance, the microdischarges are established in acetylene, thin films with a thickness of several namometres are formed on surfaces, which increase and stabilize the surface tension up to a level of 72 mN m−1. The state of the art of this new technology is discussed.

A new method for the measurement of apparent contact angles at the global energy minimum on real surfaces has been developed. The method consists of vibrating the surface, taking top-view pictures of the drop, monitoring the drop roundness, and calculating the contact angle from the drop diameter and weight. The use of the new method has been demonstrated for various rough surfaces, all having the same surface chemistry. In order to establish the optimal vibration conditions, the proper ranges for the system parameters (i.e., drop volume, vibration time, frequency of vibration, and amplitude of vibration) were determined. The reliability of the method has been demonstrated by the fact that the ideal contact angles of all surfaces, as calculated from the Wenzel equation using the measured apparent contact angles, came out to be practically identical. This ideal contact angle has been compared with three methods of calculation from values of advancing and receding contact angles.

Polypropylene electrets 20-μm thick obtained in a corona discharge were studied. After the electrets were charged, they were put into a vacuum chamber at various pressures and the electret surface potential was measured over a 1-h period. A desorption from the electrets is suggested to explain the results obtained.

High-modulus polyethylene (PE) tapes were grafted with acrylic acid using a two-step procedure. The tapes were first subjected to He/Ar corona discharge, immediately followed by exposure of the corona-treated tapes to acrylic-acid-saturated He gas. Evidence for the grafting was provided by X-ray photoelectron spectroscopy, which showed the surface of the treated tapes to consist of 64% acrylic acid and 36% PE. The grafting of acrylic acid is confined to the outermost surface layers, as indicated by reflection infra-red spectroscopy. Pull-out tests showed that the corona grafting of acrylic acid improves adhesion to epoxy resins by a factor of eight. Moreover, the increased adhesion is not achieved at the expense of a decrease in mechanical properties of the high-modulus PE tapes.

The decrease in the corona treatment effect with time and its influence on the flexographic printability of low-density polyethylene-coated paperboard were studied. After corona treatment, sheets were stored in different ways. Some sheets were stored in a laboratory atmosphere, while others were protected from exposure to light, air, moisture and dust in polyethylene bags. The tendency for ink to spread on the surfaces was studied using contact angle measurements. Printability was evaluated as print density, dot gain, uncovered (white) and mottling. The results obtained show that the surface energy of the protected sheets decreased with time, but not as much and not as quickly as that of the unprotected sheets. In the case of the protected sheets, the percentage uncovered areas and mottling remained constant, but for the unprotected sheets they increased with increasing time after the corona treatment. No significant differences were seen in the other print quality measures. Copyright © 2005 John Wiley & Sons, Ltd.
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