The aim of this publication is to describe an industrial application of the oxyfluorination process to polymer webs. Controlled oxyfluorination of polymer surfaces is a solventless, highly efficient and cost-effective technique of surface modification. The adhesive properties of oxyfluorinated polypropylene films are largely improved so that a variety of solventand water-based printing inks used in contact printing technology can be used. We have confirmed that, in many cases, the necessity to employ an expensive top-coating process that uses acrylic primers to optimise the film printability, can be avoided. The oxyfluorination process with its long lasting effect is a competitive alternative to the simple corona discharge treatment. The oxyfluorination ALKOR' SURFOX process can be described as an environmentally responsible technology that delivers a broad range of products possessing many exceptional surface properties.

In adhesion applications, the rapid ageing of corona discharge pretreated surfaces is a well-known problem. Very often the corona treatment has to be renewed just before the application. Oxyfluorination process presents an interesting alternative to the corona discharge treatment. In this work, the outstanding ageing properties of the oxyfluorinated polyolefin surfaces are described on the basis of acid–base surface characteristics.

The effects of argon glow discharge and selected organic solvents on the surface wettability of poly(ethylene terephthalate) (PET) and on the wettability decay of glow discharged PET films were studied. Glow discharge in argon (30 W/1 min) drastically reduced the initial water contact angle (CA) measurement of PET from 67.0 to 26.2°. The glow-discharge-induced wetting, however, decayed during the first 7 days and stabilized at 33.1°. Treatments in dimethyl sulfoxide, dimethyl formamide, pyrdine, and water at 80°C caused some improvement in surface wettability as shown by decreases of water CAs in the range of 53–56°. When the solvent and glow discharge treatments were applied consecutively on PET, additive effects on improving surface wettability were observed. The stabilized water CAs of the solvent-and-glow-discharged films ranged from 25.0 to 32.1° depending upon the solvent type. The solvent treatments prior to glow discharge either reduced the extent of CA decay or the time taken to reach stabilization on PET films. Scanning electron microscopic evaluation showed no difference between the solventtreated and the untreated PET surfaces, but a finely etched surface was observed on the glow discharged PET at a 40,000 magnification and above. The distinctly different surface of the DMSO-and-glow-discharged PET indicated that morphological changes on PET surface were induced by the solvent.

Ultrahydrophobic polymeric surfaces were prepared using two plasma chemistry approaches: (1) fluorocarbon plasma polymerization, and (2) simultaneous argon plasma etching of polypropylene (PP) surfaces and sputtering of poly(tetrafluoroethylene) (PTFE) onto these rough surfaces. In the first case, several fluorinated monomers were selected to study the effect of the monomer structure on the plasma polymer morphology and wettability. Ultrahydrophobic surfaces were generated for those monomer gases that were capable of forming powders. For fluoromonomers that did not form powders, the wetting characteristics were similar to that of PTFE. Plasma polymerization of perfluorohexane does not lead to powder deposition and the highest advancing water contact angle measured was 118° (the receding contact angle was 74°). Fluorinated acrylates and ethyl heptafluorobutyrate were tested as well and in all cases, the powder formation of the polymer led to highly hydrophobic surfaces (advancing and receding contact angles between 164°–174° and 8°–173°, respectively). In the second technique, argon plasma was used to etch PP surfaces, creating a rough surface (the roughness is controlled by the reaction time). Simultaneously, PTFE was sputtered onto the roughened PP surface to create fluorinated surfaces. The most hydrophobic surface exhibited an advancing contact angle of 172° and a receding contact angle of 169°. AFM and SEM analyses of these samples show that the powder deposition of the polymers and the etching of PP concurrent with the sputtering of PTFE lead to rough surfaces resulting in a highly nonwettable surface.

The effects of acid oxidation on the surface properties of gel-spun ultra-high modulus and molecular weight polyethylene (UHMWPE) fibers were investigated. Three acid-assisted reactions with CrO₃ (I), K₂Cr₂O, (II), and one base-catalyzed reaction with K₂Cr₂O₇ (III) were studied. In reaction II, two levels of sulfuric acid were used for IIa and IIb, with reaction IIa containing the higher concentration. Under the reaction conditions chosen, i.e. 1 min at 23°C, the effects of these oxidations were restricted to the fiber surfaces. All oxidation reactions either significantly reduced or eliminated the axially oriented macrofibril striations and changed the lamellae perpendicular to the fiber axis to irregular hairline surface structures. The oxidative attacks on the fiber surfaces appeared to have occurred in the fibrillar structure and likely at the disorder regions along the fibrils. The epoxy resin wettability and the interfacial adhesion to the epoxy resin were both improved with reactions I and IIa, whereas reaction III did not affect either of these properties. A positive relationship between surface wettability and interfacial adhesion on single fibers was observed on the untreated and acid oxidized gel-spun UHMWPE fibers.

Ellipsometrically determined adsorption isotherms are reported for water, bromobenzene, nitro-methane, benzene, amyl, butyl, propyl, and ethyl alcohols, carbon tetrachloride, n-octane, and n-hexane on a polished polytetrafluoroethylene surface. These are nonwetting systems, and contact angles were also measured. In addition, isotherms were determined for two wetting systems, carbon tetrachloride on oxide-coated stainless steel and n-hexane on oxide-coated chromium-plated glass. For most of the nonwetting cases, the film pressure of the adsorbed film was not negligible, and should not not be omitted in semiempirical treatments of contact angle. The isotherms may be fitted by a previously proposed potential-distortion model, the choice of parameters also giving the observed contact angle. Alternatively, the isotherms are found to be segments of a single characteristic isotherm of the Polanyi type and thus obey a corresponding state principle. This characteristic isotherm for nonwetting systems does not fit the data for the two wetting cases, and the possibility is discussed that in the nonwetting cases the adsorbed state consists of bulk-like liquid in the form of micropatches or lenses rather than as a film of uniform thickness.

In this paper, a polymeric coating based on the modified chlorinated polypropylene (CPP) emulsion was synthesized, methyl methacrylate (MMA), butyl acrylate (BA) and acrylic acid (AA) were grafted onto CPP backbone and phase inversion was conducted to obtain waterborne emulsion. Results showed that the concentration of initiator (BPO) had the greatest effect on graft copolymerization. The concentration of emulsifier and temperature influenced the results of phase inversion. Besides, the thermal performances of modified CPP were better than untreated one. In addition, the coating obtained in optimum condition had excellent adhesion to BOPP film, and apparently improved the printing quality of the film. The printability promotion should be attributed to the different movement trend of coating’s polar and un-polar chains during the baking step, as well as the subsequent formations of new coating/substrate and coating/ink interface layer.

The surface energetics and acid-base character of paper handsheets were investigated using dynamic contact angle analysis. The surface energies were calculated using both geometric and harmonic mean methods. The surface acid-base property was characterized by calculating the work of acid-base interaction according to Fowkes' theory. To evaluate the effect of sizing on the paper surface properties, handsheets with various sizing treatments were studied in comparison with unsized handsheets. It was found that the sizing on the paper handsheets tends to reduce the surface energy and cover the acid-base sites. The results also show that the handsheet surface can be characterized directly using contact angle analysis.

Plasma polymer interactions are actively being studied because of their unique ability to surface modify polymers without affecting their bulk properties. Plasma polymer interactions are characterized by those which result from the addition of molecules to the polymer surface and by those which result from polymer bond rearrangement. Surface crosslinking is a bond rearrangement reaction, and gives rise to the following surface property improvements: improved adhesion (l), improved absorption (2), and improved resistance from environmental attack (heat, ultraviolet radiation). Plasma induced surface crosslinking has been studied for a period in excess of ten years. Previous experiments have measured the existence of surface crosslinking as a function of the gas used for the plasma and the technique by which the plasma has been produced (3-6). These studies have completely neglected the plasma properties which were responsible for the surface crosslinking. This approach has failed to provide a comprehensive picture which explains the experimental data and has resulted in the requirement that the polymer be in physical contact with the plasma. The present experiment investigates the coupling mechanism which exists between the plasma and the polymer. The results of the experiment demonstrates that ultraviolet radiation (uv), produced by a hydrogen glow discharge, is sufficient to account for plasma induced surface crosslinking of high density commercial polyethylene. Physical contact between the plasma and the polymer is not required.

Nitrogen plasmas at atmospheric pressure produced by 2.45 GHz microwaves at a power density of approximately 10 MW m^-3 have a degree of ionization less than about 10^-7. Nevertheless they have interesting and potentially important effects on polymer and metal surfaces exposed to them. An experimental programme is underway to identify the active species in the plasma and its afterglow. This paper describes a simplified model of the chemical kinetics in the plasma that allows species concentrations to be estimated in a range of conditions, for comparison with experimental data. It predicts a high degree of dissociation combined with low gas temperature in microwave-generated plasmas.

The effect of roughness of a solid surface on its wettability by a liquid has been studied theoretically using mechanistic arguments. By calculating the equilibrium shape of a liquid drop resting on a rough surface, we obtain the relation between the true (or microscopic) equilibrium contact angle at the three-phase contact line and the apparent contact angle observed macroscopically at the geometrical contour plane of the solid. By extending a proposal of Shuttleworth and Bailey, we provide a plausible explanation for hysteresis of the drop shape and contact angle which we evaluate for solid surfaces with concentric grooves. To calculate the equilibrium drop shape of a liquid on a solid surface whose roughness is more realistic than concentric grooves, we employ a perturbation method of solving approximately the Young-Laplace equation for the shape. Although the hysteresis in contact angle and drop shape cannot be evaluated by the method, the apparent contact angle and the local contact line positions are approximately predicted when the surface roughness has the form of cross grooves, hexagonal grooves, and radial grooves. Surfaces having random roughness are also considered and a modified form of the well-known Wenzel equation is derived which includes a factor for surface texture in addition to the conventional roughness factor.

Wetting, the process of water interacting with a surface, is critical in our everyday lives and in many biological and technological systems. The contact angle is the angle at the interface where water, air and solid meet, and its value is a measure of how likely the surface is to be wetted by the water. Low contact-angle values demonstrate a tendency of the water to spread and adhere to the surface, whereas high contact-angle values show the surface’s tendency to repel water. The most common method for surface-wetting characterization is sessile-drop goniometry, due to its simplicity. The method determines the contact angle from the shape of the droplet and can be applied to a wide variety of materials, from biological surfaces to polymers, metals, ceramics, minerals and so on. The apparent simplicity of the method is misleading, however, and obtaining meaningful results requires minimization of random and systematic errors. This article provides a protocol for performing reliable and reproducible measurements of the advancing contact angle (ACA) and the receding contact angle (RCA) by slowly increasing and reducing the volume of a probe drop, respectively. One pair of ACA and RCA measurements takes ~15–20 min to complete, whereas the whole protocol with repeat measurements may take ~1–2 h. This protocol focuses on using water as a probe liquid, and advice is given on how it can be modified for the use of other probe liquids.

Surface energies of solids can be estimated using contact angles of liquids of known surface tension and susceptibilities for polar or acid-base interactions. Interfacial tensions and work of adhesion can be calculated using these estimated energies. There are three circumstances in which performance or bond strengths are related directly to surface energies: when separation occurs interfacially, when interfaces are not completely wetted, and when third phases are present at the interface.

Adhesion of polymers was determined as a function of temperature. The influence of the bonding times and temperatures indicates that the performance is established largely by the extent of wetting at the polymer-substrate interface. Considerations based on surface free energies show that most practical systems should exhibit complete wetting at equilibrium. The problem appears to involve establishing factors which retard or preclude wetting. Low substrate surface energy, high polymer viscosity, substrate topography, selective adsorption, and coacervation may be involved.

A critical review of some fundamentals of surface chemistry revealed several areas in which current interpretations of data or interrelationships are erroneous or misleading.

Correct forms of fundamental equations interrelating surface energies, equilibrium contact angles and adhesion are given and plotted in a convenient, illuminating, dimension-less form. These curves provide a basis for comparing some recently published empirical equations with the fundamental ones showing that discrepancies result from changing values of the interaction parameter φ.

In this paper we describe the preparation and preliminary characterization of diblock copolymers with a low surface energy block. These polymers were prepared by modifying the isoprene block in styreneisoprene-based block copolymers with either short perfluoroalkyl or dimethyl siloxy ‘fingers’. Specifically, the diene block of a styrene-isoprene block copolymer containing a large proportion of pendent vinyl groups (1,2- and 3,4-isoprene) was reacted with the appropriate hydrosilane in the presence of non-acidic Pt catalyst. The degree of attachment of hydrosilane was as high as 50% of the pendent unsaturations. Pendent vinyl groups were converted more efficiently than pendent methyl vinyl groups. These block copolymers, when mixed with the styrene homopolymer, exhibited surface segregation behaviour which depended on both polymer molecular weight and processing conditions. The surface segregation properties of the resulting block copolymers were studied by a variety of techniques which include contact angle measurements, and either X-ray photoelectron spectroscopy or Rutherford backscattering spectrometry. Contact angles as high as 110° were measured for both the siloxane- and perfluoroalkane-modified materials.

The effect of plasma treatment on surface characteristics of polyethylene terephthalate films was investigated using helium and oxygenated-helium atmospheric plasmas. Sample exposure to plasma was conducted in a closed ventilation test cell inside the main plasma chamber with variable exposure times. The percent weigh loss of the samples showed an initial increase followed by decrease with extended exposure time, indicating a combined mechanism of etching and redeposition. The wettability as measured by the contact angle showed a sharp initial increase followed by a steady-state trend with increased exposure time, suggesting a change in surface functionality. Atomic force microscopy analysis revealed increase in surface roughness, as well as evidence of redeposition of etched volatiles. Functionality changes were measured using X-ray photoelectron spectroscopy and these changes were correlated to the new plasma-induced properties. © 2004 The Electrochemical Society. All rights reserved.

In order to investigate the effect of atmospheric pressure plasmas on adhesion between aramid fibers and epoxy, aramid fibers were treated with atmospheric pressure helium/air for 15, 30 and 60 s on a capacitively-coupled device at a frequency of 5.0 kHz and He outlet pressure of 3.43 kPa. SEM analysis at 10 000× magnification showed no significant surface morphological change resulted from the plasma treatments. XPS analysis showed a decrease in carbon content and an increase in oxygen content. Deconvolution analysis of C1s, N1s and O1s peaks showed an increase in surface hydroxyl groups that can interact with epoxy resin. The microbond test showed that the plasma treatment for 60 s increased interfacial shear strength by 109% over that of the control (untreated). The atmospheric pressure plasma increased single fiber tensile strength by 16-26%.

Ion bombardment of polymer surfaces is a method used in promoting metal/polymer adhesion. The adhesion of these multicomponent interfaces can be attributed to chemical bonding, physical bonding, or a combination of both. By evaluating the resistivity of thin films of Cr, TaSiz, Pd and Au deposited on polymer, the interfacial reactivity was determined, and the contribution due to chemical bonding identified. The adhesion strength of these interfaces, determined by peel strength measurements, increases with interfacial reactivity. Interfacial reactivity increases with the total energy of all the ions bombarding the polymer surface (dosage). Cr and TaSi₂ show extensive interfacial reactivity than noble Au and Pd.

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.

Thermally stimulated currents (TSC) are studied in the temperature range between 30 and 130°C on positively corona-charged high-density polyethylene films. TSC spectra from these charged films strongly depend on the order of the processes: heat-treatment of the sample films prior to charging and vacuum deposition of metallic electrodes. They also depend on the electrode materials. Observed TSC behaviors are explained in terms of the thermal influence of the vacuum deposition of metallic electrodes. Charge stability of these charged films is also studied for samples with Al and Bi electrodes.

Ethylene-co-tetrafluoroethylene copolymer (ETFE) films were modified by four plasmas: direct and remote H2 plasmas and direct and remote O2 plasmas; and the hydrophobic recovery process of these plasma-modified surfaces was investigated using water contact angle measurements and angular XPS. The water contact angle measurements showed important aspects for the hydrophobic recovery process. (1) All plasma-modified ETFE surfaces, regardless of the kind and mode of plasmas, showed increases in the contact angle with increasing aging time. The increase continued for 5 days after finishing the plasma modification, and stopped after 5 days. (2) The plasmamodified surfaces after the aging process never reverted back to the same level of the contact angle as for the unmodified (original ETFE) surfaces. (3) The contact angle after the aging process was strongly dependent on to what plasma the ETFE surfaces were exposed in the modification. (4) The aging temperature influenced the contact angle value after the aging process. The angular XPS measurements also provided a detailed description of the chemical composition of the topmost layer. (1) The chemical composition at the topmost layer of the surfaces altered during the aging process. (2) CH₂-CH₂-CHF, and CH₂-CHF-CH₂ and CH₂-CH(OH)-CF₂ groups disappeared from the topmost layer during the aging process; and CH₂-CH₂-CH₂, and CH₂-CH₂-CF2 and CH₂-CH(OH)-CHF groups appeared at the topmost layer. (3) Such disappearance and appearance occurred on all plasma-modified surfaces regardless of the kind (H₂ or O₂ plasma) or mode (direct or remote plasma) of plasmas used for the modification. This may be due to segmental mobility of CH₂-CH₂-CH₂ sequences rather than of CF₂-CF₂-CF₂ sequences.