A method has been devised to determine the acid/base parameters of reference liquids as absolute numbers, and not as values relative to a conventional set of parameters for water. Contact angle measurements are employed, using three liquids on three solids. The theory calls for the solution of nine simultaneous, nonlinear equations in nine variables–and unreasonably formidable task.

A preliminary set of solutions has been computed, for one set of polar liquids on five solids. These results must be rejected on grounds of physical reasonableness. They also fail the test of predicting liquid-liquid interfacial tension, which for miscible liquids must be negative or zero.

Wetting on ambient, heterogeneous surfaces is characterized by contact angle hysteresis. Quantitative models of contact angle hysteresis are essential in order to design surfaces with specific wetting behavior or to interpret experiments seeking to characterize a surface through its wetting properties. We focus on the successes and failures of theoretical models as well as experiments on model surfaces in describing contact angle hysteresis on ambient surfaces. We describe experimental observations of contact line structure and dynamics as well as contact angle hysteresis on laboratory surfaces. We discuss three general classes of models treating one-dimensional periodic heterogeneity, two-dimensional periodic heterogeneity, and random heterogeneity. We show where these models succeed and where they fail to agree quantitatively and qualitatively with experimental observations. New models treating strong, dense heterogeneity as well as temporal relaxation of contact angles in experimental environments need to be developed to provide quantitative descriptions of contact angle hysteresis on ambient surfaces.

Ion Irradiation on polytetrafluoroethylene(PTFE) has been carried out to improve adhesion to metal and to adhesive cement. Argon ion was irradiated on the polymer, and amount of Ar⁺ was changed from 10¹⁴ ions/cm² to l×10¹⁷ ions/cm² at 1 keV, and 4 ml/min of oxygen gas was flowed near the polymer surface during the ion irradiation. Wetting angle was changed from 100 degree to 70 - 150 degree depending on the ion beam condition. The changes of wetting angle and effects of Ar⁺ irradiation in oxygen environment were explained in a view of surface morphology due to the ion beam irradiation onto PTFE and formation of hydrophilic group due to a reaction between irradiated polymer chain and the blown oxygen. Strongly enhanced adhesions were explained by interlock mechanism, formation of electron acceptor groups on the modified PTFE, and interfacial chemical reaction between the irradiated surface and the deposited materials.

Modified surfaces of polyethylene terephthalate)(Mylar® or PET film) have been studied by surface energetics, ESCA, atomic force microscopy (AFM), and optical profilometry. For the surface energetics studies, receding contact angle titrations were used to evaluate the surface functional groups in the outer few angstroms of the surface. This sensitive method of determining the contact angle with buffer solutions of different pHs allows one to investigate the nature of the chemical species introduced by the various energetic treatments. The data are consistent with a surface that is covered by a low density of carboxylic acid moieties in the case of corona and flame treatments, applied in a high-speed commercial type of a process at low doses. The high contact angle hysteresis indicates that the coverage is moderately heterogeneous but on a very small length scale, less than a few micrometers. ESCA qualitatively supported this, although this technique is not optimum for the low degrees of surface modification. A comparison is made of the two surface treatments in terms of depth of penetration, roughness, and surface density of chemical moieties introduced. UV laser-treated surfaces showed no indication of surface chemical modification.

Hydrophilic polymer surfaces are desirable for many applications, such as adhesion and wettability. In this study, we have developed a tenaciously bound hydrophilic surface coating which can be applied to a hydrophobic polymer using a plasma treatment process. In this process, porous polyethylene (PE) was used and pretreated with the plasma discharge of an oxidizing gas, eg carbon dioxide. The treated surface, containing mainly anionic groups, was then soaked in a polycation solution, eg polyethyleneimine (PEI). A tenaciously bound hydrophilic coating was formed due to multiple anchors (ionic interactions) between PEI and the plasma-treated surface. The coated surface was characterized using water contact angle goniometry and X-ray photoelectron spectroscopy (XPS). Both the stability and the durability of the coating have been evaluated using various storage conditions and repeated washing in water. The coating process developed in this study is useful in many applications which require a permanent and lasting wettable polymer surface.

Joining of thermoplastic composite primary structures is an area of great importance in the aerospace industry. In order to achieve a strong and durable joint, an effective surface treatment is needed. Preadhesion surface treatment of thermoplastic composites is limited due to their chemical inertness to aggressive chemicals or mechanical treatments. The feasibility of using a new technique of ArF UV (193 nm) excimer laser irradiation as a preadhesion treatment of PEEK (polyaryletheretherketone) reinforced with carbon fibers is demonstrated. This method presents an alternative to other limited and polluting conventional surface treatment methods, such as sand blasting, etching or welding. Experimental results indicated that laser preadhesion treatment significantly improved the shear and tensile adhesion strength of various structural epoxy adhesives FM 300 2K and AF 163-2 bonded to PEEK composite adherends compared with untreated and SiC blasted substrates. Best results were obtained with laser pulse fluences of 0.18 or 1 J/Pcm2. Shear strength of laser treated PEEK composite joints improved by 450% compared with that of untreated PEEK composite and by 200% compared to SiC blasted adherends, at ambient and at—30 C and 120 C temperatures. An order of magnitude improvement was found in the tensile strength of laser treated PEEK composite in a sandwich structure compared to non-treated or abraded sandwich joints. The mode of failure changed from interfacial to cohesive as the number of pulses or laser energy increased during treatment. A similar improvement was achieved in fracture toughness (Mode I and II) performance of laser treated compared to abraded or non-treated PEEK composite adherends. Surface analysis of laser treated adherends and of the fractured joints revealed surface cleaning (XPS), morphology changes (Scanning Electron Microscopy), chemical modification (FTIR spectroscopy and XPS), changes in crystallinity (X-ray) and in wetting property (contact angle), all correlated with the laser irradiation improving the joint’s performance. The bulk properties of the PEEK composite adherend did not deteriorate by the laser irradiation during treatment, as indicated by the identical flexural strength before and after laser treatment. Durability tests showed no change in performance of joints produced from laser treated adherends compared to untreated and abraded ones, even after exposure of 60 days at 60 C/95% RH. It can be concluded that the excimer laser has a potential as a precise, clean and simple preadhesion surface treatment for PEEK composite.

Synthetic and analytical procedures for the preparation of surface-functionalized polyolefins are described within the general context of polymer surface functionalization. Chemistry leading to simple functionalization of both polyolefins in general and polyethylene in particular is described. Selected examples of further chemistry leading to graft copolymers attached to these surfaces are described. The effects of such graft chemistry leading to various sorts of chemically modified surfaces with different solvent-polymer interactions specific to the graft microstructure and to temperature are discussed.

The effect of CO₂-laser treatment on the wettability of mild steel is presented. In addition, data are presented on the initial joint strengths and durability of joints formed between a single-part epoxide and both mild steel and aluminium. A large increase in stressed durability performance was observed with the laser-treated aluminium compared with degreased-only controls. The laser treatment was shown to efficiently remove the organic contamination from the metallic substrates. Auger analysis showed that the laser interacts more with the mild steel than the aluminium adherends, to produce a relatively thick surface oxide. The changes to the mild steel surface introduced by the CO₂-laser treatment facilitate an durability trials was greater with the laser-treated adherends than with degreased-only controls.

This study focused on the behavior of the paper-polypropylene-paper (PPP) laminate while aging in hot oil in the absence of voltage stress. The results provide an understanding of both the quality of the interfacial bond and the performance of this bond during service. X-ray photoelectron spectroscopy performed on two different peeled laminates suggest that the bond failed primarily adhesively. Weibull statistical analysis of the peel strength data obtained on unaged laminates and those aged in polybutene oil at 90°C for 120 hours showed that the strength loss is consistent with one failure mechanism and the failure rate increases with applied stress. For the aged sample, Weibull analysis results are consistent with the prior loss of peel strength due to the aging. Experiments on the solubility of the oil show that lamination reduces the amount of absorption in comparison to the unlaminated composite. Swelling experiments on the individual components show differential swelling between the paper and polypropylene to be the source of the strength loss. The polypropylene swells, and the paper shrinks. Measurements on the laminate show that both paper and polypropylene shrink, indicating that the paper governs the laminate swelling process. During aging, the differential swelling generates internal stresses on the interface. In addition to yielding the magnitudes of these stresses, finite element analysis also predicts plastic deformation and creeping of the polypropylene as well as tensile stresses between the paper and polypropylene at a free edge. Very likely these processes damage the bond and contribute to the loss of bond strength.

The different methods available in the literature to calculate the surface tension of a solid from contact angle measurements are discussed and compared. The discussion is based on the contact angles of water, glycerol, and diiodomethane measured at 20°C on the surface of a side-chain liquid crystalline polymer. Some discrepancies exist among the results obtained with the different methods, mainly between the values yielded by Neumann's equation and those obtained with approaches that postulate the decomposition of the surface tension into several terms associated with different types of molecular interactions (methods of Owens and Wendt and of Good and van Oss). The physicochemical basis of these various treatments is discussed.

The surface free energy and surface structure of poly(tetrafluoroethylene) (PTFE) film treated with low temperature plasma in O₂, Ar, He, H₂, NH₃, and CH₄ gases are studied. The contact angles of the samples were measured, and the critical surface tension γ_c (Zisman) and γ_c (max) were determined on the basis of the Zisman's plots. Furthermore, the values of nonpolar dispersion force γ^a_s, dipole force γ^b_s, and hydrogen bonding force γ^c_s to the surface tensions for the plasma-treated samples were evaluated by the extended Fowkes equation. Mainly because of the contribution of polar force, the surface free energy and surface wettability of PTFE film which was treated with H₂, He, NH₃, Ar, and CH₄ for a short time increased greatly. Electron spectroscopy for chemical analysis (ESCA) shows that the reason was the decrease of fluorine and the increase of oxygen or nitrogen polar functional group on the surface of PTFE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1733–1739, 1997
https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1097-4628(19970328)63:13%3C1733::AID-APP4%3E3.0.CO;2-H

Silicone polymers exhibit good mechanical properties for a variety of biomedical and industrial applications. For instance, silicone rubber has been used for voice prostheses, urinary catheters, contact lens material, and icing coating materials. However, their inherently high hydrophobicity limits certain applications of this material despite its favorable mechanical properties6. Plasma treatment of silicone polymers may affect their hydrophobicity and therewith their boundability to other materials without affecting the bulk properties. Plasma treatment often involves progressive oxidation of the surface and cross-linking of surface molecular groups which inhibits migration of low molecular weight oligomers to the surface. Various gases have been used to modify silicone polymers by plasma treatment, such as oxygen, helium, ammonia, carbon dioxide, nitrogen and argon. Frequently a thin cross-linked, sometimes water washable, silica-like surface layer was produced by plasma treatment, but there is no consensus about the nature of the chemical groups produced at the outermost surface. The surface hydrophilicity created by plasma treatment is often lost over time. This so-called hydrophobic recovery can be influenced by the storage conditions, whether in air or in liquid, temperature or subsequent adsorption of a surfactant.

Low-pressure plasma-treatments aimed to selectively graft-NH2 groups onto the surface of conventional polymers such as polyethylene, polystyrene and polyethyleneterephtalate are described. The combined use of plasma and surface diagnostics allowed elucidation of the effect of the experimental parameters on the extent of the surface modifications and to understand chemical mechanisms involved in the surface processes. The diagnostic approach is essential for engineering polymer surfaces with a dosed relative density of-NH2 groups, for scale-up and process transfer.

A method of preparing modified surfaces, referred to as soft-landing, is described in which intact polyatomic ions are deposited from the gas phase into a monolayer fluorocarbon surface at room temperature. The ions are trapped in the fluorocarbon matrix for many hours. They are released, intact, upon sputtering at low or high energy or by thermal desorption, and their molecular compositions are confirmed by isotopic labeling and high-resolution mass measurements. The method is demonstrated for various silyl and pyridinium cations. Capture at the surface is favored when the ions bear bulky substituents that facilitate steric trapping in the matrix.

Careful measurements of the surface tension of solid polymers, y_s°, based on the data on contact angles for wetting liquids with various surface tension, y_L°, allows one to establish the functional dependence of y_s° = f(y_L°). This dependence is divided into three zones: one zone, where there is no dependence of y_s° on y_L° and two zones where y_s° changes linearly with y_L°.

It was shown that when polyurethanes designed for use in biopolymer applications were immersed in orienting fluids, significant increases in their non-dispersive surface energies took place. The kinetics of the surface energy response were found to be a function of the immersion medium's acid-base interaction potential. Restructuring from the as-cast state, similar to that reported for two-component polyurethane adhesives, occurs in response to thermodynamic demands and is attributable to a preferential concentration of low energy segments in the surface region. Since shifting surface energies in polyurethanes may pose problems in biological applications, an attempt was made to crosslink the surface of the polymers by the use of cold, microwave plasma discharges with Argon as the treatment gas. Plasma treatments proved to be successful, in that polyurethane surfaces so modified responded much more weakly to changes in the polarity of contact media.

Such polymers are commonly used as release coatings for pressure sensitive adhesive tapes. In this paper the bulk, surface, and interfacial structures of polyvinyl N-alkyl carbamates having either decyl or octadecyl side chains are examined. The bulk structures and thermal transitions were characterized using X-ray scattering and differential scanning calorimetry. Dynamic mechanical thermal analysis was used to investigate thermal transitions and rheology (i.e., segmental mobility) of the polyvinyl N-alkyl carbamates. The surface energies of polyvinyl N-alkyl carbamate coatings were determined using contact angle methods, while X-ray photoelectron spectroscopy and static secondary ion mass spectrometry were employed to characterize the near-surface compositional profiles of the coatings. The peel force provided by the polyvinyl N-alkyl carbamate coatings, as a function of aging time and temperature, was measured for a tape having an acrylic acid containing alkyl acrylate based pressure sensitive adhesive. The changes in peel force with aging time and temperature were related to the ability to maintain a stable interfacial structure between the PSA and polyvinyl N-alkyl carbamate coatings. Changes in the interfacial composition upon aging were characterized by comparing the surface compositions of the PSA and polyvinyl N-alkyl carbamate coatings initially, prior to contact, as well as after aging and peeling them apart. The increase in peel force upon aging can be attributed, in large part, to a restructuring at the PSA/polyvinyl alkyl carbamate interface. Energetically favorable acid-base interactions between the basic urethane and acetate groups in the polyvinyl alkyl carbamates and the acrylic acid groups in the PSA provide a driving force for the restructuring. If the segmental mobility within the polyvinyl alkyl carbamate is sufficient, restructuring can occur, leading to increased concentrations of these groups at the PSA/polyvinyl alkyl carbamate interface, resulting in higher attractive forces and greater adhesion. The propensity for the polyvinyl N-alkyl carbamate coatings to restructure upon contact with a polar medium was also characterized by monitoring the receding contact angle of water, as a function of water contact time and temperature. A good correlation is seen between the ability of the polyvinyl alkyl carbamate coatings to provide a low peel force for the acrylate PSA tape and the ability of the coatings to maintain a high water receding contact angle.

Ar⁺1 ion irradiation on a polycarbonate (PC) surface was carried out in an oxygen environment in order to investigate the effects of surface chemical reaction, surface morphology, and surface energy on wettability of PC. Doses of Ar⁺ ion were changed from 5 × 10¹⁴ to 5 × 10¹⁶ at 1 keV ion beam energy by a broad ion beam source. Contact angle of PC was not reduced much by Ar⁺ ion irradiation without flowing oxygen gas, but decreased significantly as Ar⁺ ion was irradiated with flowing 4 sccm (ml/min) oxygen gas and showed a minimum of 12° to water and 5° to formamide. A newly formed polar group was observed on the modified PC surface by Ar⁺ ion irradiation with flowing oxygen gas, and it increased the PC surface energy. On the basis of x-ray photoelectron spectroscopy analysis, the formed polar group was identified as a hydrophilic CO bond (carbonyl group). In atomic force microscopy (AFM) study, the root mean square of surface roughness was changed from 14 Å to 22–27 Å by Ar⁺ ion irradiation without flowing oxygen gas and 26–30 Å by Ar⁺ ion irradiation with flowing 4 sccm oxygen gas. It was found that wettability of the modified PC surface was not greatly dependent on the surface morphology, but on an amount of hydrophilic group formed on the surface in the ion beam process.

Surfactants — an acronym for surface-active agents — are versatile and ubiquitous chemicals. They are found in industrial areas related to detergents (Hancock 1984; Thayer 1993), pharmaceuticals (Tadros 1984; Attwood and Florence 1983), cosmetics (Ainsworth 1993), paints (Nylen and Sunderland 1965), pesticides (Wada et al. 1983; Tann, Berger and Berger 1992) and oil recovery (Neustalder 1984), to mention a few. Mother Nature used them, long before humans, as major building blocks of biological membranes, taking advantage of the so-called hydrophobic effect (Tanford 1980). This chapter focuses on applications of surfactants in liquid film coating processes, and in particular in coatings involving aqueous solutions, as encountered in the photographic industry.

Wetting is basic to coating. Initially air contacts the solid, and during coating the liquid displaces the air from the moving solid surface so that none is visible in the coated film. Thus, coating is a process of dynamic wetting. For uniform coating, the wetting line must remain straight and advance steadily. At sufficiently high speeds, however, the wetting line becomes segmented and unsteady as a thin air film forms between the solid and liquid. The air film disrupts the uniformity of the coated film, and often air bubbles appear in the coating. Dynamic wetting failure limits coating speed.

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.

Surface modification of Kapton polyimide film (325 nm thick) by means of chromic acid and perchloric acid at different times and temperatures has been carried out. The contact angle of water decreased from 82 to 55° and the surface energy increased accordingly from 26 to 45 mJ/m² with times of etching by chromic acid up to 45 min at 33°C. Etching at higher temperatures increased the surface energy. Chromic acid was more effective than perchloric acid. IR and XPS studies indicated multiple bonding and generation of poler groups on the surface. The peak at 1778 cm^-1 due to the imide group decreased on acid etching. The O/C ratio increased and the N/C ratio decreased. The peel strength of the joint polyimide film/copper film/epoxy adhesive/aluminium sheet increased about two-fold on modification of the polyimide (PI) film at 33°C for 45 min, although the changes were marginal for the PI film/silicone rubber/PI film joint. The peel strength is a function of the time and temperature of etching.