Polycarbonate surfaces have been treated with radiofrequency plasmas of oxygen, air and argon to hydrophilise the surfaces and to provide good cell culture properties. Surfaces treated at high RF power/gas flow ratios were highly hydrophilic and stable towards washing in 70% ethanol, while those treated at lower ratios were not wash-stable. Cell growth properties as good as on commercial tissue-culture polystyrene could be obtained down to 20° water contact angle (measured after ethanol washing) on the treated surfaces for three different human cell lines (HeLa cervix carcinoma cells, MRC-5 lung fibroblasts and Chang hepatoma cells). The HeLa cells were most sensitive to the treatment conditions, while the Chang cells showed the most robust behaviour. Cells grown on surfaces with around 20° water contact angle were assessed by immunofluorescence staining methods and phase contrast microscopy. The cells showed normal behaviour with respect to morphology, spreading, cytoskeleton structure, cell-surface contacts and DNA synthesis.

The modifications induced by excimer laser irradiation of poly(ether ether ketone) (PEEK) surfaces have been investigated as a function of the laser process parameters for laser fluences below the material ablation threshold. In the case of 193 nm laser treatment, a significant increase in the adhesion properties of PEEK was obtained due to the formation of new polar and reactive groups on the surface. The extent of these reactive groups has to be controlled since their presence in high concentration may also have a negative effect on the mechanical properties of the treated surface. Laser treatments using 248 nm radiation did not result in a significant increase in the adhesion properties of PEEK. This probably results from thermal degradation of the surface at this laser wavelength.

The modifications induced by excimer laser radiation on different types of polymer surfaces (polyether-etherketone (PEEK), polycarbonate (PC) and epoxy resin) performed at laser fluences below the material ablation threshold have been investigated. Particular attention was given to the role of laser irradiation wavelength (193 or 248 nm) on the nature and properties of the treated surfaces. Results indicate that a much stronger reactivity was obtained after treatments at 193 nm for all the investigated polymers. At this wavelength, the original polymer surfaces are strongly modified by UV photons; surface reorganization occurs and polar groups induce an increase in the surface wettability.

The chemical modifications induced on PET by an excimer laser radiation or a lowpressure plasma were studied by XPS and Tof SIMS analyses. Both treatments induced surface oxidation but differences related to the type of oxidized groups and the level of degradation of the treated surface were evidenced. Both treatments can significantly enhance the adhesion but the surface change responsible for the improvement was different for each pretreatment.

The thermodynamic aspects of the evolution of surface free energy of acrylic acid grafted polyethylene films have been examined as a function of time of contact on water. The dispersive and polar components vary with time and the interfacial free energy reaches a minimal value. Two terms participate in these variations: adsorption of water molecules and reorientation of polar acrylic groups at the water-polymer interface. Irreversible process thermodynamics has been applied to these phenomena. The surface can be characterized by a phenomenological coefficient relating the orientation rate and the orientation affinity of the polar groups at the interface.

Characterization of poly(ethylene terephthalate) (PET) films surfaces through wettability measurements and inverse gas chromatography techniques leads to a better knowledge of the potential interactions with a coating. An important case is the one relative to gelatin coatings for photographic films. In order to favor adhesion on PET, it is of interest to examine the problem in terms of acid–base interactions. PET is found amphoteric and gelatin rather basic. Several surface treatments on PET like orientation on water and flame or plasma treatment in air lead to an increase in surface acidity. Adhesion with gelatin as determined by the peel test is increased through a flame treatment, because of the higher acidity of PET and subsequent chemical bonding at the interface. Determination of acid-base surface properties of PET and gelatin appears to be an excellent tool for adhesion prediction.

The reorganization of the surface of a polyethylene grafted with 1% acrylic acid during contact with water has been studied using contact-angle measurements, a color test, esterification, inverse gas chromatography and ESCA spectroscopy. The evolution of the surface properties of the polymer in contact with water is explained by movements of the macromolecular chains followed by the orientation at the surface of the acrylic grafts, initially buried in the bulk of the polymer. The concept of “potential” surface energy of a polymer is proposed.

The surface of the bio-material polymethyl methacrylate (PMMA) was treated with CO₂, Nd:YAG, excimer and high power diode laser (HPDL) radiation. The laser radiation was found to effect varying degrees of change to the wettability characteristics of the material depending upon the laser used. It was observed that interaction with CO₂, Nd:YAG and HPDL effected very little change to wettability characteristics of the PMMA. In contrast, interaction of the PMMA with excimer laser radiation resulted an increase in a marked improvement in the wettability characteristics. After excimer laser treatment the surface O₂ content was found to have increased and the material was seen to be more polar in nature. The work has shown that the wettability characteristics of the PMMA could be controlled and/or modified with laser surface treatment. However, a wavelength dependence of the change of the wetting properties could not be deduced from the findings of this work.

The manufacture of polyolefin films by an extrusion process will today almost certainly include as part of the processing line some form of adhesion promoter. For Cast and Blown extrusion this would mean corona as the adhesion promoter. Often overlooked as being an insignificant component on the manufacturing line, the Corona Treater is often purchased in haste and without adequate deliberation. Without this consideration a capital expenditure may arise that may meet current requirements but offers little or no flexibility for the future. When considering a Corona Treater, first and foremost a choice must be made between Bare Roll and Covered Roll. This paper deals with the decision making process leading up to this determination. We will stress that one should not allow any preconceived notions to cloud the issue on the type of treater station required. Both Bare Roll and Covered Roll treater stations serve a particular purpose and play an integral part in the manufacturing process.

The formation of the interface between aluminium and O₂ or CO₂ plasma-modified poly(ethylene terephthalate) (PET) has been investigated by X-ray photoelectron spectroscopy (XPS). As demonstrated by the changes in the C 1s, O 1s, and A1 2p core level spectra upon A1 deposition, the metal was found to react preferentially with the original ester, with the plasma-induced carboxyl and carbonyl groups to form interfacial complexes. The phenyl ring at the modified PET surface was seen to be involved in the formation of the interface, but to a lesser extent. This confirms the high reactivity of the oxygen-containing groups towards the deposited A1 atoms. The adhesion between A1 and the plasma-modified PET films was evaluated by means of a 180° peel test. A considerable (up to ten times) improvement in adhesion was achieved by plasma treatment of the PET substrate, but for either plasma gas the adhesion strength was found to depend strongly on the plasma power and treatment time. The results are discussed in terms of the concentration of oxygen-containing groups at the polymer surface, the surface topography, and the possible presence of low-molecular-weight materials at the metal-polymer interface.

PET (Polyethylene terephthalate) films were modified with two different plasmas, nitrogen and oxygen, as a function of treatment times and RF powers. Firstly, the chemical composition of the plasma-modified PET films was investigated by XPS. In the case of nitrogen plasma, the formation of amine, imine and amide groups is detected. A slight diffusion of nitrogen-containing species into the PET bulk is also observed by angle-resolved XPS measurements. The appearance of alcohol, carbonyl and carboxyl functions is observed in the case of oxygen plasma treatment. After thermal deposition of an aluminium film, peel tests reveal that the Al/PET adhesion increases as follows: untreated < nitrogen plasma < oxygen plasma treatment.

Secondly, after sevderal successive depositions of thermally evaporated Al on oxygen plasma treated PET film, XPS was used to study the chemistry at the interface. The XPS results reveal that the additional reactive sites created on the PET surface by the treatment explain the significant improvement in Al/PET adhesion observed for plasma-modified samples.

Chemical modification of the PET surface by carbon dioxide plasma treatment has been studied using X-ray photoelectron spectroscopy (XPS). The plasma process results mainly in the formation of carbonyl, carboxyl, and carbonate groups at the PET surface. Under rather mild treatment conditions (low plasma power combined with a short treatment time), the formation of CO bonds was found to be dominant, whereas the formation of highly oxidized carbon or double-bonded oxygen-containing groups required a high plasma power or a relatively long treatment time. The treatments performed under excessive conditions frequently led to degradation at the polymer surface. Angle-resolved XPS analyses performed on a freshly modified PET film showed a slight decrease in the O/C atomic ratio when the take-off angle (TOA) increased, indicating a relatively uniform distribution of oxygen within the sampling depth (estimated to be about 8 nm at 80° TOA). The chemical composition of the plasma-modified surface was found to be relatively stable on extended storage in air under ambient conditions. The decrease in oxygen-containing groups at the carbon dioxide-plasma-treated PET surface upon ageing is mainly ascribed to the surface rearrangement of macromolecular segments, the loss of oxygen-containing moieties introduced by the plasma treatment, and the possible migration of non-affected PET chains from the bulk to the surface region.

The surface tensions of a series of poly(isobutylenes) in the molecular weight range 400–3000 have been determined at 24°C. These results, together with surface tension values from the literature for poly(dimethyl siloxanes) and three series of different pure chain-molecule homologues, are found to exhibit a linear dependence on (molecular weight)^{$\text{−2}\text{2}$}. A simple free-volume argument seems to be consistent with this empirical observation.

The increased use of polyphenylene sulphide (PPS) and polyetheretherketone based composites for aircraft structures has highlighted the need for reliable methods of bonding these materials to metallic components such as titanium. Both composite and titanium adhesive bonds exhibit poor long-term durability when exposed to hot/wet conditions, aerospace fluids and solvents. As a result, surface treatments are employed to enhance surface energy, surface roughness and alter surface chemistry to provide better long-term durability. In this initial study the adhesive bonding of glass fibre reinforced GFR-PPS and commercially pure titanium was investigated. Prior to bonding, both materials were plasma treated using argon and oxygen gases in a RF discharge. Surface characterisation was carried out to optimise these treatments. Surface energy and wettability were examined using contact angle analysis, surface roughness was examined using scanning electron microscopy and atomic force microscopy, while X-ray photo-electron spectroscopy (XPS) was employed to study the surface chemistry. Bond strengths were determined using lap shear tests. Initial results reveal that these optimum plasma treatments produce a significant increase in bond strength.

Corona discharge treatment of poly(ethylene terephthalate) (PET) films produces chemical and physical modification of the surface leading to the formation of cavities and bumps. The roughness of the surface increases with the time of treatment and may be detected by scanning electron microscopy for the samples treated above 10 cycles, which corresponds to the duration of the exposure of the film under the electrodes. The degree of chemical modification, producing OH groups, is observed by adsorption of radioactive calcium ions and contact angle measurements. The results of these measurements are discussed and evidence presented shows that increase of the surface density of functional groups up to the value of 0.2 × 10¹⁴ sites/cm² leads to a rapid increase in wettability of PET films.

Molecular dynamics simulations have been carried out for liquid water between flat hydrophobic surfaces. The surfaces produce density oscillations that extend at least 10 Å into the liquid, and significant molecular orientational preferences that extend at least 7 Å into the liquid. The liquid structure nearest the surface is characterized by “dangling” hydrogen bonds; i.e., a typical water molecule at the surface has one potentially hydrogen‐bonding group oriented toward the hydrophobic surface. This surface arrangement represents a balance between the tendencies of the liquid to maximize the number of hydrogen bonds on the one hand, and to maximize the packing density of the molecules on the other. A detailed analysis shows that the structural properties of the liquid farther from the surface can be understood as effects imposed by this surface structure. These results show that the hydration structure of large hydrophobic surfaces can be very different from that of small hydrophobic molecules.

A new method for preparing wettability gradients on polymer surfaces was developed. Wettability gradients were produced on low density polyethylene surfaces by treating the polymer sheets in air with corona from a knife-type electrode whose power gradually increases along the sample length. The wettability gradient surfaces prepared by the corona discharge treatment were characterized by the measurement of water contact angle, Fourier-transform infrared spectroscopy in the attenuated total reflectance mode, electron spectroscopy for chemical analysis, and scanning electron microscopy. The gradient surfaces prepared can be used to systematically investigate the interactions of biological species in terms of the surface hydrophilicity/hydrophobicity of polymeric materials.

In order to functionalize the surface of blown low-density polyethylene (LDPE) and cast polypropylene (CPP) films, and ultimately to maximize the attachment of active molecules onto them, the optimum treatment parameters of capacitively-coupled radio-frequency (13.56 MHz) oxygen plasma were investigated by using contact angle, toluidine blue dye assay, X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR). Contact angle values of LDPE and CPP samples decreased significantly after oxygen plasma treatment. They further decreased as the plasma power level increased. The treatment time had no substantial effect on contact angle value. The optimum treatment conditions for LDPE and CPP films for maximizing carboxyl functionality without causing observable surface changes were found to be 200 W/200 mTorr and 250 W/50 mTorr, respectively, when treated for 3 min. The maximum carboxyl group concentration obtained with LDPE and CPP films were 0.46 and 0.56 nmol/cm², respectively. The percent of oxygen atoms on the surface of plasma-treated LDPE and CPP films was determined by XPS analysis to be 22.6 and 28.7%, respectively. The ATR-FTIR absorption bands at 1725–1700 cm⁻¹ confirmed the presence of carboxylic acids on LDPE and CPP films. By exposing the plasma-treated sample to air rather than water and treating films repeatedly with oxygen plasma, a higher carboxyl group concentration could be obtained. Copyright © 2008 John Wiley & Sons, Ltd. https://onlinelibrary.wiley.com/doi/abs/10.1002/pts.829

The adhesion between a polymer and a solid substrate may be considered to be one type of complex liquid-solid interaction. Relationships between surface wettability and bulk properties of liquidlike polymers are discussed. A new and direct empirical relationship between the glass temperature (T_g) and critical surface tension of a polymer (γ_c) is established:

This study is aimed at understanding the controversy between the surface tension component (STC) theory and the equation of state (EQS) approach for interfacial tensions. We attempt to relate molecular interactions to various components of surface tension. Molecular interactions consist of electrostatic (ES), charge transfer (CT), polarization (PL), exchange-repulsion (EX), dispersion (DIS), and coupling (MIX) components. These interactions can be the basis for the STC theory involving Lifshitz-van der Waals (LW) and the short range acid-base (AB) or donor-acceptor interaction. Each of these components is shown to contain two major parameters. New equations for the interaction energy and surface tension for polar molecules are proposed to include the ES and EX parameters, which happen in some cases to balance each other or nearly cancel out without being detected. The roles of molecular interactions on adhesion, adsorption, contact angle, and wettability are illustrated through the spreading coefficient S, the Hamaker coefficient A, and Derjaguin's disjoining pressure . We have found that the STC theory is applicable to the systems involving either physisorption or chemisorption, whlie the EQS applies to those involving ony physisorption.

The donor—acceptor interaction(1,2) and the acid—base interaction(3) have been reviewed. On many occasions, the two terms, though different, have been used interchangeably to describe the interactions involving the exchange of electrons between a donor and an acceptor. For polymer adhesion, Fowkes(4,5) and Bolger et al. (6) have pointed out the important role of the acid-base interaction in the formation of an adhesive bond.

In 1967, Lee published two papers on adhesion of high polymers^(1,2) on the basis of the Buche—Cashin—Debye equation⁽³⁾

where D is the molecular diffusion constant, η the bulk viscosity, A Avogadro’s number, ρ the density, k Boltzmann’s constant, T the absolute temperature, M the molecular weight, and R ² the mean-square end-to-end distance of a single polymer chain. It was concluded that the physical state of the polymer determines the major adhesion mechanism involved. Polymer adhesion can be subdivided into rubbery polymer-rubbery polymer adhesion (R—R adhesion), rubbery polymer—glassy polymer adhesion (R—G adhesion), and rubbery polymer—nonpolymer—solid adhesion (R—S adhesion). Diffusion, which depends to a great extent on the physical state of a polymer, is actually a limited selective process. Thus, diffusion of rubbery polymers can take place at the interface, but diffusion of a glassy polymer at a viscosity of 10¹³ poise or a diffusion constant of 10^-21 cm²/sec appears to be nearly impossible. On the other hand, physical adsorption is common to all three types of the above adhesion systems.

In this paper, we report our unexpected finding about the correlation between Lewis acid−base surface interaction components and linear solvation energy relationship (LSER) solvatochromic parameters α and β. In 1987, van Oss, Chaudhury, and Good proposed to split the asymmetric acid−base parts of a bipolar system into separate surface tension components:  Lewis acid (electron acceptor) γ⁺ and Lewis base (electron donor) γ^-. It was assumed that the ratio of γ⁺ and γ^- for water at 20 °C was to be 1.0. With that ratio as a reference, the base components, γ^- for other liquids, biopolymers, polymers, and solids appeared to be overestimated. Recently, we unexpectedly found a correlation for liquids between γ⁺ and γ^-, and α (solvent hydrogen-bond-donating ability) and β (solvent hydrogen-bond-accepting ability) introduced since 1976 by Taft and Kamlet. From that correlation, we obtained a more realistic ratio for the normalized α and β values for water at ambient temperature to be 1.8 instead of 1.0. Based on this new ratio, we calculated total surface tensions for related materials at 20 °C. They are generally unchanged as expected, despite the considerable, favorable change in the γ⁺ and γ^- values in the direction of lowering the Lewis basicity. The predicability of solubility with interfacial tension is also unaffected. For example, the sign of those negative interfacial tensions that favor solubility remains the same. In addition, the implications of other LSER parameters, e.g. Π* and δ_H², on surface properties will be briefly mentioned.

We present our new findings about the causes of discrepancies between the measured and calculated liquid-liquid interfacial tensions derived from contact angles. The calculated ones are based on either the equation developed by Fowkes or that by van Oss, Chaudhury and Good (VCG), while the measured ones are based on the sessile drop, weight-volume by Jańzuk et al. and the axisymmetric drop shape analysis (ADSA) by Kwok and Neumann. Indeed, there are deviations between the calculated and measured results. For an immiscible liquid-liquid or liquid-solid interface, we prefer to employ Harkins spreading model, which requires the interfacial tension to be constant. However, for the initially immiscible liquid-liquid pairs, we propose an adsorption model, and our model requires the interfacial tension to be varying and the surface tensions of bulk liquids at a distance from the interface to remain unchanged. Thus, the difference between the initial and final interfacial spreading coefficients (S_i) equals the equilibrium interfacial film pressure (π_i)_e. According to our findings, the calculated interfacial tension represents the initial value (γ₁₂)_o, which differs from the equilibrium value (γ₁₂)_e obtained experimentally after some time delay. This expected gap at a reasonable time frame is chiefly caused by the equilibrium interfacial film pressure between the two liquids. The initial (or calculated) interfacial tension can be positive or negative, while the equilibrium (or measured) one can reach zero. In fact, the former is shown to have more predictive value than the latter. A negative initial interfacial tension is described to favor miscibility or spontaneous emulsification but it tends to revert to zero instantaneously. Thus, a miscible liquid mixture should have zero interfacial tension. In response to recent papers by Kwok et al., we show that the disagreements between the calculated and measured interfacial tensions are definitely not caused by the failure of the VCG approach. Correct interfacial tensions are calculated for liquid pairs containing formamide or dimethyl sulfoxide (DMSO) by using the dispersion components cited in Fowkes et al.'s later publication. With the corrected surface tension components, the equilibrium interfacial film pressures (π_i)_e's for at least 34 initially immiscible liquid pairs have been calculated. These values are generally lower than the corresponding spreading pressures π_e's obtained by others using the Harkins model. Recently, we established a relationship between these two film pressures with the Laplace equation and found a new criterion for miscibility to be (π_i)_e = π_e.