Polystyrene and polyethyleneterephthalate surfaces were exposed to helium, oxygen/helium and nitrogen/hydrogen plasmas singly and in combination. The treated surfaces were evaluated by water contact-angle measurements and by x-ray photoelectron spectroscopy. It was found that the oxygen and nitrogen tend to graft to common carbon atoms, to form amide groups. The water wettability was found to correlate with the fraction of electronegative atoms incorporated into the surface. © 1998 John Wiley & Sons, Ltd.
https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/%28SICI%291096-9918%28199808%2926%3A9%3C674%3A%3AAID-SIA414%3E3.0.CO%3B2-5

Water absorption by the basestock during coating affects coating pickup and coating mass distribution and, thus, the properties of the coated paper. This work presents results of experiments that were designed to separate the effects of two important factors that determine sheet absorbency: hydrophobic sizing and porosity. Bleached kraft handsheets with a broad range of pore size, void fraction, and roughness were sized to different levels with a solution of alkyl ketene dimer (AKD) in non-swelling hexane. A lightweight coated (LWC) basestock was treated similarly. Coating was performed at 762 m/min on a cylindrical laboratory coater. The effect of hydrophobic sizing on coating pickup depended greatly on sheet porosity and roughness. On dense-smooth sheets, sizing resulted in lower coating pickup. On rough sheets, including LWC basestock, the effect of sizing on pickup was concealed by the overwhelming effect of roughness on the metering action. Coating uniformity and holdout were very good on the dense-smooth sheets (although sizing gave a slight reduction) and poor on the porous rough sheets and LWC basestock (sizing had little effect). The results suggest that coating holdout and uniformity are determined mainly by sheet surface structure (porosity and roughness) and not by sizing.

The interfacial adhesion of ultrahigh-modulus polyethylene (UHMPE) fibre–vinylester composites was improved by the oxygen plasma treatment of the UHMPE fibre. The chemical functional group formations on the UHMPE fibre surface by oxygen plasma treatment were analysed using diffuse reflectance Fourier transform infrared spectroscopy and the morphological changes of the UHMPE fibre surface by plasma etching were observed by scanning electron microscopy. The wettability enhancement by the chemical functional group formation and the mechanical interlocking due to the micropits were important factors in improving the interfacial adhesion of the UHMPE fibre–vinylester composites by oxygen plasma treatment. In order to investigate the relative importance of the two factors, wettability enhancement and mechanical interlocking, in the improved interfacial adhesion of the UHMPE fibre–vinylester composites, nitrogen plasma treatment was also performed. Nitrogen plasma treatment of the UHMPE fibre was proved to be effective in the formation of the micropittings and ineffective in the chemical functional group formation in comparison with the oxygen plasma treatment. The interlaminar shear strengths of the nitrogen-plasma-treated UHMPE fibre–vinylester composites showed almost the same value as those of the oxygen-plasma-treated UHMPE fibre–vinylester composites. The wettability enhancement and mechanical interlocking are important in the improvement of interfacial adhesion of UHMPE fibre–vinylester composites by plasma treatment and mechanical interlocking seems to be more important.

Surfaces of poly(ethylene terephthalate); PET, films were irradiated with Ar⁺ at 1 keV using various ion doses (ID) from 10¹⁴ to 10¹⁷ ions/cm² (isc) with and without an O₂ environment. The wettability of the modified surfaces of PET was determined by measuring the contact angle between water droplets and the modified surfaces. The modified surfaces were also characterized by AFM (atomic force microscopy) and XPS (X-ray photoelectron spectroscopy) for changes in the surface morphology, and the chemical composition and molecular structure, respectively. The contact angle decreased from 70° for unmodified surfaces to 45° for modified surface with ID = 10¹⁴ isc without O₂ and remained relatively constant with higher ID. The contact angle, however, reached a minimum value of 8° for modified surfaces with ID = 10¹⁶ isc with O₂. The improved wettability may be due to a combination of the formation of hydrophilic groups, chemical and molecular structural changes, physical structural or morphological changes, and increased roughness of the surface. The wettability of the modified surfaces also depended on the time of exposure to air. The wettability worsened with exposure time to air, but was revived by immersing the films into water. Possible mechanisms for the change of the wettability of the modified surfaces are given.

The present invention is a method and apparatus for treating a polyester support such as polyethylene napthalate or polyethylene terephthalate. The treatment is carried out at near atmospheric pressure in a gas of helium and nitrogen or oxygen. The treatment uses anodized aluminum electrodes and an atmospheric glow discharge results when the electrodes are connected to an RF generator and spaced about 2 mm apart. The process and apparatus improve adhesion of subsequently coated emulsions on the polyester support.

We have used Time of Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) in combination with X-ray photoelectron spectroscopy (XPS) to study chemical changes taking place at the surface of pure cellulose paper samples treated in N2 plasma for periods of time up to 60 seconds. High resolution TOF-SIMS spectra permit the detection of various functionalities containing nitrogen, even following very brief (∼2s) plasma exposure. Correlations between chemistry and surface properties, such as water wettability, are presented and discussed.

This paper reviews recent studies on the mechanism of corona treatment of polyolefin films, specifically the chemical and physical changes of this process and the self-adhesion mechanism. Corona discharge of polymeric films introduces polar groups into the surfaces, which increases the surface energy and, as a consequence, improves substrate wettability and adhesion. The main chemical mechanism of corona treatment is oxidation. In addition, corona treatment can crosslink surface regions and increase the film cohesive strength.

This chapter presents after a short reminder of thermodynamic definitions, the most commonly used techniques for surface tension measurements with some details of the most interesting of them for high temperature applications. Some recent results on the evaluation of the influence of external factors, like the surrounding atmosphere, on the determination of the surface tension of molten systems are also presented. ASTRA is an experimental methodology and an integrated software to get and process data of drop shape profiles to determine surface and interfacial tension and contact-angle values. Due to its high performances in terms of time of acquisition and reliability, it is particularly suitable for both static and dynamic measurements. Indeed, by using ASTRA it is possible to reach up to two interfacial tension measurements per second, having access to dynamic measurements over very large time scale. ASTRA is currently used both for liquid metals and for liquid systems at room temperature.

This chapter discusses the physico-chemical hydrodynamics of rising bubble. At small Reynolds numbers effective approximate analytical methods allow to characterize different states of dynamic adsorption layers quantitatively: weak retardation of the motion of bubble surfaces, almost complete retardation of bubble surface motion, transient state at a bubble surface between an almost completely retarded and an almost completely free bubble surface. The measurement of bubble terminal velocity in water cannot be used for the experimental verification of these theories because uncontrolled impurities in water immobilize a small bubble surface almost completely without any addition of surfactant. The rising bubble velocity relaxation caused by the dynamic adsorption layer (DAL) formation can be measured. The DAL study is more realistic for large bubbles and large Reynolds numbers (Re) because trace concentrations of surface active impurities cannot retard the bubble surface movement completely.

This chapter focuses on the maximum bubble pressure method (MBPM) and deals with the physico-chemical and hydrodynamic processes taking place at various stages of the growth of a bubble and its separation from a capillary. Particular emphasis is made on theoretical problems like surface tension calculation from the measured excess pressure, surface tension calculation from the measured excess pressure, splitting of time interval between consecutive bubbles into lifetime and deadtime, and calculation of these characteristic times involving inertial and viscous properties of liquid and gas, non-stationarity of flows, etc. Emphasis is also made on experimental details like measurements of pressure and bubble formation frequency and optimisation of the geometry of capillary and measuring system related to the application of the MBPM. The results presented in this chapter contribute both to an improvement of the commercially available devices, and to a better understanding of the method by the users, helping them in the application of the MBPM and in a correct interpretation of the results.

The CPT has consequently been employed with several configurations and with different methodologies to measure the interfacial tension of pure liquids and for studying the dynamics of adsorption on different time scales both on earth and in microgravity. Some of these methodologies are described in detail, discussing the critical aspects and the main experimental results. Capillary Pressure (CP) tensiometry is especially helpful for studying liquid/liquid interfaces. Microgravity represents an ideal tool for studying the dynamic aspects of adsorption of soluble surfactants and the CP tensiometry is the most suitable technique for these kind of studies in this environment, both for liquid-liquid and liquid-vapor interfaces. However, provided that the Bond number is sufficiently small, CP tensiometry can also be used in normal laboratory conditions.

The spinning drop technique (SDT) has been developed to measure extremely low interfacial tensions (from 10 ^-6 mNm ^-1 to 10 mNm ^-1). It uses profile analysis of deformed droplets similar to the pendent drop method. Unlike in pendent drop experiments, where the droplets are deformed by the gravitational force, SDT is based on the balance of centrifugal and interracial forces in rapidly rotating systems. Apart from purely tensiometric applications SDT has been found to be a versatile tool for surface and interface science. It allows the study of adsorption phenomena and even permits the “simulation” of spontaneous structure formation processes, e.g., the break-up of liquid threads and the coalescence of droplets. This chapter reviews both standard and non-standard SDT applications. After a brief description of basic principles and properties, the equilibrium properties of a rotating drop, i.e., its shape and its stability, are considered in detail. Experimental aspects of SDT: Both commercial and laboratory SDT set-ups are introduced. Problems arising from sample preparation (particularly in the case of highly viscous polymers) and the determination of the droplet dimensions are discussed.

This chapter focuses on the drop volume technique. The stalagmometer is the most primitive version of the drop volume method. It allows only a very rough estimate of the surface tension of a liquid. With the drop volume technique an accurate determination of the volume of a drop formed at the tip of a given capillary is obtained. The measuring procedure is realized by means of a precise dosing system, which forms drops continuously at the capillary. The method has restrictions for example with respect to the drop formation time. If drops are formed too fast the measured drop volumes are no longer a measure of the surface tension alone but are in addition governed by chaotic effects leading to so-called drop volume bifurcations. A drop volume experiment is described is this chapter.

This chapter discusses axisymmetric drop shape analysis (ADSA) and its application. It provides an account of these ADSA methodologies. It contains a description of the numerical algorithms and their implementation. The applicability of ADSA is illustrated extensively for the investigation of surface tension measurements with pendant and sessile drops and contact angle experiments with sessile drops using both axisymmetric drop shape analysis - profile (ADSA-P) and axisymmetric drop shape analysis - diameter (ADSA-D). The advantages of pendant and sessile drop methods are numerous. In comparison with a method such as the Wilhelmy plate technique, only small amounts of the liquid are required. Drop shape methods easily facilitate the study of both liquid-vapor and liquid-liquid interfacial tensions. Also, the methods have been applied to materials ranging from organic liquids to molten metals and from pure solvents to concentrated solutions. There is no limitation to the magnitude of surface or interracial tension that can be measured: The methodology presented in this chapter works as well at 10³ mJ/m ² as at 10 ^-3 mJ/m ².

The present invention provides a method of modifying the surface of a polymeric substrate, e.g., to improve the wettability of the polymer film surface and/or alter the reactivity of the surface of the substrate by further oxidation or affixation of nitrogen, comprising exposing the substrate to a flame. The flame is supported by a fuel and oxidizer mixture that includes an effective amount, for modifying the polymeric substrate, of at least one compound that functions as a fuel or oxidizer substitute and is selected from an oxygen-containing compound, in which the oxygen comprises between about 10 and 50 atomic percent of the compound, a nitrogen-containing compound or an oxygen-nitrogen-containing compound. In a preferred embodiment, which affixes nitrogen or nitrogen-containing chemical groups onto the surface of the film, the flame is supported by a fuel and oxidizer mixture that includes ammonia, nitrous oxide, nitric oxide or a mixture thereof in an effective amount. Large increases in the ASTM wetting test, e.g., greater than 13 mJ/m² over that reported with conventional flame-treating processes, have been observed in films treated according to this invention. In addition, significant increases in polymer film surface oxidation levels, e.g., as much as 55 percent, have been observed, as have significant amounts of nitrogen and nitrogen-containing chemical groups affixed to film surfaces.

The plasma source ion implantation (PSII) was utilized to improve the wettability and the stability of surface layer formed in the modification of polymeric materials. Polystyrene was treated with different kinds of plasma ions to render the surface more hydrophilic or hydrophobic. Hydrophobic recovery of PSII-treated polystyrene was also observed as a function of aging time, aging temperature, and treatment parameters. Treatment parameters involve kinds of gases, pressure, plasma power, pulse frequency, pulse voltage, etc. To study the effect of inert gas on hydrophobic recovery, polystyrene samples were prepared by helium, argon, or gas-mixture treatment. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been used to interpret the PSII-treated polystyrene surface and its hydrophobic recovery, with the assistance of x-ray photoelectron spectroscopy and water contact angle measurements. TOF-SIMS spectra of O218 PSII-treated samples showed the presence of O18-containing peaks from the modified surfaces. PSII modifications provide more stable surfaces of polystyrene as a function of aging time than plasma treatments. The comparison of aging behavior data allowed for examination of the differences in the stability of the functionality introduced by the two different treatment techniques.

A detailed X-ray photoelectron spectroscopy study of a plasma-modified polystyrene (PS) surface was carried out after N₂ plasma treatment. PS surfaces were found to be highly hydrophilic and reactive as it readily picks up oxygen giving rise to oxyfunctionalities on the surface. The plasma treatment also led to a slow chain scission with carboxyl, forming carbonate linkage.

In this paper, we briefly discuss several ways to determine the work of adhesion and the requirements for achieving maximum adhesion and spontaneous spreading. Specifically, we will concentrate on the methodology developed by van Oss. Chaudhury and Good [5–7] for the determination of the work of adhesion and interfacial tension. Recently, Good [4] has redefined the surface interaction components γ⁺ and γ⁻ as hydrogen bond acidic and basic parameters. We have related the surface−hydrogen−bond components γ⁺ and γ⁻ to the Taft and Kamlet's [28, 29] linear solvation energy relationship (LSER) solvatochromic α and β parameters. We [8, 9] have found that, for water at ambient temperature, α [hydrogen-bond-donating (HBD) ability] and β [hydrogen-bond-accepting (HBA) ability] are not equal, and the ratio for the normalized α and β is 1.8. This new ratio is assumed to be equal to that of γ⁺ & γ⁻ for water at 20°C. On the basis of the new ratio, we will present our recalculated surface-hydrogen-bond components for several polymers and biomaterials. This change in the ratio did not affect the total surface tension or the sign of the interfacial tension. The net improvement is in the lowering of the γ⁻ values. These data may be useful for predicting the adhesion between an adhesive and an adherend.

Plasma-induced low-density polyethylene (LDPE) radicals were studied in detail by electron spin resonance (ESR) by its comparison with ESR of high-density polyethylene (HDPE). The observed ESR spectra of plasma-irradiated LDPE are largely different in pattern from those of HDPE. The systematic computer simulation disclosed that such observed spectra consist of three kinds of radicals, midchain alkyl radical (1), allylic radical (2) as discrete radical species, and a large amount of dangling bond sites (DBS) (3) at an intra- and intersegmental cross-linked region. All these component radicals are essentially identical to those of HDPE. One of the most special features unique to plasma-irradiated LDPE, however, is the fact that thermally stable DBS (3) is a major component radical instead of a midchain alkyl radical in HDPE. This can be ascribed to the difference in polymer morphology between LDPE and HDPE:  branched structure with a large amount of amorphous region for LDPE and linear structure with a large amount of crystalline region for HDPE. Since one of the characteristics of plasma irradiation is the fact that it is surface-limited, LDPE would undergo the radical formation preferentially on the surface-branched structural moiety followed by facile cross-link reactions resulting in the formation of DBS. Thus, the nature of radical formation of PE was found to be affected by the polymer morphology in a very sensitive manner.

The nature of peroxy radical formation from plasma-induced surface radicals of polyethylene (PE), both low-density polyethylene (LDPE) and high-density polyethylene (HDPE), was studied by electron spin resonance with the aid of systematic computer simulations. It was found that peroxy radical formation varies with the structure of component radicals of plasma-irradiated PE, both LDPE and HDPE:  Among three plasma-induced radicals of PE, dangling bond sites (DBS) undergo an instant conversion into the corresponding peroxy radicals in contact with oxygen, while the midchain alkyl radical is of very low reactivity with oxygen in both LDPE and HDPE. Computer simulations disclosed that ESR spectra of peroxy radicals are similar to each other in LDPE and HDPE, both being composed of two types of spectra, a partial >em>g-averaging anisotropic spectrum and a nearly isotropic single line spectrum due to different molecular motional freedom at the trapping sites of peroxy radicals.

The chemical modification of polystyrene surfaces by low-energy (10−100 eV) SF₅⁺, C₃F₅⁺, and SO₃⁺ ions was studied by X-ray photoelectron spectroscopy and two-laser ion trap mass spectrometry. The mechanism of fluorination was found to be dissimilar for SF₅⁺ and C₃F₅⁺ ions in this energy range at fluences of 10¹⁴−10¹⁶ ions/cm². SF₅⁺ was found to induce fluorination of the polymer surface by grafting reactive F atoms upon dissociation at impact. SF_n fragments were not found to be grafted or implanted into the polymer. Sulfur was detected on the polymer surface only at incident energies above 50 eV and was found to be sulfidic in nature. In contrast, C₃F₅⁺ ions induced grafting of both reactive F atoms and molecular C_mF_n fragments from the dissociation of the incident projectile. Larger proportions of highly fluorinated sites and thicker fluorocarbon layers were found for C₃F₅⁺ at all energies and fluences. A variety of aliphatic and aromatic fluorine bonding environments were detected on both SF₅⁺ and C₃F₅⁺ modified polystyrene surfaces.

Plasma surface treatment of plastics is definitely not new, nor is it commonplace. What is a plasma and what can it do is the subject of the following paper. A plasma is an excited gas, not unlike the aurora borealis. The excited particles that comprise the plasma bombard materials placed within their environment causing permanent change to their surface properties. By the judicious selection of process gas(es) and process parameters, the surface can be reengineered to fit specific needs. This paper presents quantitative analytical data on the chemical changes to the surface of polyethylene subjected to a plasma.

Copper films evaporated on argon-oxygen plasma-treated poly(phenylene-vinylene) films have been studied by scratch test, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The adhesion of the metallic film to the polymer substrate was greatly enhanced after treatment and found to increase with the treatment time. SEM observation of the treated samples revealed that the morphology of the polymer surface was gradually changed with the treatment time as compared with that of the bare polymer film. On the other hand, XPS analysis of the polymer-metal interface showed that the bonding between carbon, oxygen and copper were subsequently modified as compared with those obtained in untreated samples. The high adhesion strength observed on these substrates was related to the modification in the surface morphology on the one hand and to the formation of new compounds at the polymer-metal interface on the other. The nature of the interfacial layer and its influence on the adhesion of the copper layer was discussed by comparing the results with those obtained in poly(phenylene-vinylene) (PPV)-Al systems.