It is recognized that the non-dispersive components, γ^ab, of the surface free energies, γ, play an important role in the interactions of a polymer with other substrates. Because of the difficulty in measuring the surface free energy of a solid polymer surface, many methods to estimate γ have been developed. The purpose here is to examine how to characterize a high energy polymer surface using our recently proposed model and the modified two-liquid contact angle technique. First, the dispersion component, γ^d, of surface free energy of polystyrene (PS) is obtained by measuring the contact angles of water on PS surface in a series of n-alkanes. Its γ^ab is then calculated by our three-parameter semi-empirical model using the contact angle data of several key non-alkane liquids on the surface. Given the surface thermodynamic parameters, our model also enables us to calculate the interfacial free energies, γ_SL, between PS and other liquids. An attempt to relate γ_SL to the equilibrium concentrations of crazing solvents in PS is presented.

Surface biomedical effects of plasma treatment and plasma polymerization on medical-grade polyetherurethane were studied. N2 and Ar plasma treatments and hexamethyldisiloxane (HMDS) plasma polymerization were performed at a power of 100 W with exposure times ranging from 1 to 15 min. The results showed that the contact angle of water was decreased from 79° to 62° by N2 and Ar plasma treatments, and N2 plasma treatment caused a slight enhancement in anti-coagulability and anti-calcific behavior. HMDS polymerization resulted in a decrease from 79° to 43° in the contact angle and an increase from 30.5 to 37.4 s in the recalcification time. At the same time, the anti-coagulability of polymerized samples for the exposure time of 2-5 min was 2.5 times that of the untreated sample. Results of XPS and ESR analyses showed that HMDS deposited onto the polyetherurethane surface and formed new Si-N bonds, and increased the number of radicals in the sample. XPS analysis also showed that N2 and Ar plasma treatments broke some of the CO and CO bonds at the surface and resulted in oxidation of the surface.

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.

The effect of the addition of clay and TiO₂ pigments on the surface energy and surface chemistry of films made from polymers used in paper coating formulations was evaluated. The polymers were carboxymethyl cellulose, polyvinyl alcohol and a protein-based polymer - all water-soluble - and two styrene-butadiene latexes of different carboxylation levels. The morphology of the surfaces was characterized by SEM examination, gloss measurement and stylus profilometry. Chemical composition was determined by EDS and XPS techniques. Surface energy and its Lifshitz-van der Waals and acid-base components were obtained from contact angle measurements using the van Oss et al. approach. Even though the addition of pigment increasingly upset the planar surface of the films, their surface chemistry and surface energy were only slightly affected over the pigmentation range studied (up to 40% by volume) and were dominated by the characteristics of the binder polymer.

Remote argon plasma (RP) and ozone in the presence of ultraviolet light (UV–O₃) were used to render polystyrene (PS) surfaces hydrophilic in a controlled manner for eventual application in cell‐surface interaction studies. X‐ray photoelectron spectroscopy (XPS) was used to characterize both methods of modification. The degree of modification on PS was measured by an increase in surface oxygen and concomitant change in C 1s binding energies as a function of time. Both remote plasma and UV–O₃ are shown to be partially surface destructive, producing polymer fragments which are easily washed away to leave stable modified surfaces of oxidized polymer comprising of distributions of C–O, C=O and O—C=O type groups. Of the two methods, UV–O₃ is shown to be more versatile and conducive to preparing PS surfaces with controllably varying degrees of modification. UV–O₃ modified polystyrene is shown to be stable in air for at least eight months. Contact angle methods were used in correlation with XPS in characterizing UV–O₃ modified surfaces. It is shown that changes in surface tension and total surface oxygen content were related, however, not directly connected.

Polypropylene (PP), low-density polyethylene (LDPE), and high-density polyethylene (HDPE) sheets were surface-modified by radio-frequency ammonia plasmas in order to improve the strength and durability of adhesive bonding, particularly under hot and humid conditions. Surface analyses by contact angle measurements, XPS (X-ray photoelectron spectroscopy), and FTIR-ATR (Fourier transform infraredattennuated total reflection) showed incorporation, upon plasma treatment, of both nitrogen- and oxygen-containing functional groups on the polyolefin surfaces, with similar surface compositions on modified LDPE and PP. Plasma-treated polyolefin samples bonded with a cyanoacrylate adhesive possessed a high shear bond strength in ‘dry’ conditions. On exposure to hot and humid conditions (immersion in 60°C water), the bond strength decreased with time in some cases while for other samples the lap shear strength was the same after exposure to the humid environment for 1 month compared with that under 'dry' conditions. Ammonia-plasma-treated HDPE specimens displayed the best strength retention upon water immersion. The excellent durability of the bond strength under humid conditions is indicative of covalent bonding between the cyanoacrylate adhesive and amine groups, which unlike physical bonding (e.g. van der Waals interactions) is not disrupted by the ingress of water molecules. It is also possible that the structure of the interphase is in the form of an interpenetrating network, obtained through penetration of the adhesive into the plasma-modified laycr, followed by covalent bonding and curing of the penetrated adhesive.

Surface pretreatment methods to enhance adhesion to polymers with low surface energies generally either remove a region of low strength from the surface or introduce new surface functional groups. The relative importance of these two mechanisms is examined in the present paper for various combinations of pretreatment and polymer.

The growth of Cu and Al films thermally evaporated onto polyethylene (PE) and polyethyleneterephthalate (PET) surfaces is followed in situ by XPS (X-ray Photoelectron Spectroscopy) and XAES (X-ray Auger Electron Spectroscopy) from the early submonolayer stages up to the completion of a metallic film. PE and PET surfaces were metallized first without any preliminary treatment. A second series of metallization experiments were run on the polymer surfaces but pretreated by a remote O₂ microwave plasma (2.45 GHz). These metal films have also been investigated by AFM (Atomic Force Microscopy) in air. Both metals are shown not to undergo chemical interaction with low surface energy polyolefin such as PE. While an abrupt interface is seen with A1, a diffusion of Cu into the bulk of the polymer is demonstrated. Large size clusters are evidenced by AFM in the initial steps of deposition. Cu and A1 are both shown to react with PET, but not in the same way. In the case of A1, the chemical interaction across the metal/polymer interface proceeds through an electron transfer from the metal toward the ester group O=C-O. With Cu, the chemical interaction is not so clearly evidenced and the Cu is found to diffuse into the PET. Oxygenated functionalities grafted by O₂ plasma on PE and PET are C-O, C=O, O-C-O, O-C=O, and O₂C=O. The roughness of the PE and PET surfaces is observed by AFM to increase with the plasma treatment. A metal-CO type complex is clearly observed with Al/treated PE and Cu/treated PET. No chemical interaction was observed at the Cu/treated PE interface.

COF groups are formed by electron irradiation of PTFE [poly(tetrafluoroethylene)] powders in air, especially at the surface and in near-surface regions which can be easily hydrolysed to carboxyl groups by air humidity. The application of special additives during irradiation leads to modified micropowders. Fourier transform infrared (FTIR) spectroscopy enables the detection of carboxyl and COF groups. γ-Irradiation of PTFE mainly causes degradation of the polymer; the concentration of carboxyl groups is much lower. Carboxylated micropowders created via radiation treatment retain the essential properties of PTFE. With increasing radiation dose, the increasing concentration of functional groups in the micropowders causes an increase in the surface free energy. This diminishes the strong water and oil repellency of PTFE in such a way that homogeneous incorporation into aqueous and organic liquids or other polymers is possible. So, the special properties of PTFE can be made effective in these media. Modified PTFE micropowders have been successfully tested in many application areas. The aim of our present work was to increase the concentration and vary the nature of functional groups by radiation-chemical methods or chemical conversion of COF groups (polymer-analogous reactions). A highly modified PTFE powder was used to reduce the repellent properties of PTFE diaphragms for application in brine electrolysis. The COF groups of the micropowders were modified by γ-aminopropyltriethoxysilane. The irradiation of FEP [poly(tetrafluoroethylene-co-hexafluoropropylene)] and PFA [poly(tetrafluoroethylene-co-perfluoroalkylvinylether)] yields products which contain a higher content of carboxyl groups than PTFE.

Modification of a selective area of a fluororesin surface was accomplished by using ArF excimer laser radiation and a boron complex with oleophilic or hydrophilic functional groups. The chemical stability of fluororesin is attributed to the presence of C-F bonds. The F atoms were abstracted by B atoms selectively from the area irradiated with excimer laser radiation and were replaced with the desired functional groups. In this modification, B(CH₃)₃ and B(OH)₃ were used: a boron compound with methyl groups to generate an oleophilic surface, and one with hydroxyl groups to generate a hydrophilic surface. As a result, the resin surface exposed to ArF laser radiation becomes oleophilic or hydrophilic. Both samples were bonded to stainless steel plates with an epoxy bonding agent and the tensile shear strength was 1.2 x 10⁷ Pa in both cases.

Photochemical dry etching and surface modification of various polymers, e.g. polymethylmethacrylate (PMMA), polyimide (PI), polyethyleneterephthalate (PET) and polytetrafluoroethylene (PTFE) were investigated with coherent and incoherent excimer UV sources. Ablation rates of PMMA were measured as a function of laser fluence and laser pulse at the wavelength λ = 248 nm (KrF*). Decomposition and etch rates of PMMA and PI were determined as a function of UV intensity and exposure time at three different wavelengths λ = 172 nm (Xe*2), λ = 222 nm (KrCl*) and λ = 308 nm (XeCl*). The transmittance of the polymeric films was determined with a UV-spectrophotometer after different exposure times. The morphology of the exposed polymers was investigated with scanning electron microscopy (SEM). The gaseous products occurring during UV exposure were measured using mass spectrometry (MS). Chemical surface changes of the photoetched PMMA were determined by X-ray photoelectron spectroscopy (XPS). The mechanism of the photo-oxidation process of PMMA is discussed. The etching of PMMA can be explained as a result of extensive photo-oxidation. The results are compared with those obtained from mercury lamp and excimer laser experiments. Good adhesion of electrolessly deposited metal layers was achieved by irradiation of the polymeric surfaces from incoherent UV source before depositing the metal layer.

Osteointegration is dependent on a variety of biomechanical and biochemical factors. One factor is the wettability of an implant surface that is directly influenced by its surface energy. This investigation used the Zisman plot to determine critical surface energy. The effects of surface treatment, bulk grain size, and surface roughness on the critical surface tension of unalloyed titanium (Ti) were examined. Radio frequency glow discharge-treated Ti had the highest critical surface tension, followed by the passivated and heat-sterlized conditions. Titanium with no surface treatment had the lowest critical surface tension. The surface energy of Ti with an average grain size of 23 μm was not significantly different from that with a grain size of 70 μm. Surface roughness was shown to cause significant difference in measurements and definitely should be considered in studies of this kind. © 1994 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/jbm.820281206