The methods to estimate the surface tension of polymer solids using contact angles have been reviewed in the first part. They are classified into the following three groups depending on the theories or the equations applied: (1) the methods using the Young's equation alone, (2) the methods using the combined equation of Young and Good-Girifalco, and (3) the methods using the equations of work of adhesion. Some notes and comments are given for each method and results are compared with each other. The two-liquids method for rather high energy surface is also introduced.

Next, some new possibilities to evaluate the surface tension of polymer solids are presented by our new contact angle theory in consideration of the friction between a liquid drop and a solid surface. The advancing and receding angles of contact (θ_a and θ_r) are explained by the frictional tension γ_F and accordingly two kinds of the critical surface tension γ_C(γ_Ca and γ_Cr) are given.

This work has shown that one of the recommendable ways to evaluate γ_S is either the maximum γ_LV cos θ_a or the maximum γ_C using the advancing contact angle θ_a alone, and another way is the arithmetic or the harmonic mean of the γ_Ca and γ_Cr. A depiction to determine the γ_C such as ln(1 + cos θ₀) vs. γ_LV with cos θ₀ = (cos θ₀ + cos θ_r)/2 has also been proposed.

Any desired surface wettability of a plastic surface can be produced by changing the concentration of the plasma gas, which here is a mixture of oxygen and a compound which includes fluorine. In the plasma treatment, the use of a third electrode consisting of a metal mesh for ion trapping can significantly decrease the etching effect. The plastic surface wettability, given by the contact angle of a water drop, does not have any direct relationship with the surface roughness due to etching in this experiment.

ESCA and contact angle measurements were used to characterize the surfaces of Polyethylene and polypropylene films exposed to SF₆, CF₄, and C₂F₆ plasmas. None of these gases polymerized in the plasma. However, all plasma treatments grafted fluorinated functionalities directly to the polymer surfaces. SF₆ plasmas graft fluorine atoms to a polyolefin surface. CF₄ plasmas also react by a mechanism dominated by fluorine atoms, but with some contribution from CF_x-radical reactions. Although C₂F₆ does not polymerize, the mechanism of grafting is still dominated by the reactions of CF_x radicals. For all gases studied, the lack of polymerization is attributed to competitive ablation and polymerization reactions occurring under conditions of ion bombardment.

Following the development of a methodology for determining the apolar components as well as the electron donor and the electron acceptor parameters of the surface tension of polar surfaces, surfaces of a number of quite common materials were found to manifest virtually only electron donor properties and no, or hardly, any electron acceptor properties. Such materials may be called monopolar; they can strongly interact with bipolar materials (e.g., with polar liquids such as water); but one single polar parameter of a monopolar material cannot contribute to its energy of cohesion. Monopolar materials manifesting only electron acceptor properties also may exist, but they do not appear to occur in as great an abundance. Among the electron donor monopolar materials are: polymethylmethacrylate, polyvinylalcohol, polyethyleneglycol, proteins, many polysaccharides, phospholipids, nonionic surfactants, cellulose esters, etc.

Strongly monopolar materials of the same sign repel each other when immersed or dissolved in water or other polar liquids. The interfacial tension between strongly monopolar surfaces and water has a negative value. This leads to a tendency for water to penetrate between facing surfaces of a monopolar substance and hence, to repulsion between the molecules or particles of such a monopolar material, when immersed in water, and thus to pronounced solubility or dispersibility. Monopolar repulsion energies can far outweigh Lifshitz-van der Waals attractions as well as electrostatic and “steric” repulsions. In aqueous systems the commonly observed stabilization effects, which usually are ascribed to “steric” stabilization, may in many instances be attributed to monopolar repulsion between nonionic stabilizing molecules. The repulsion between monopolar molecules of the same sign can also lead to phase separation in aqueous solutions (or suspensions), where not only two, but multiple phases are possible. Negative interfacial tensions between monopolar surfactants and the brine phase can be the driving force for the formation of microemulsions; such negative interfacial tensions ultimately decay and stabilize at a value very close to zero.

Strongly monopolar macromolecules or particles surrounded by oriented water molecules of hydration can still repel each other, albeit to an attenuated degree. This repulsion was earlier perceived as caused by “hydration pressure”.

A few of the relevant colloid and surface phenomena are reviewed and re-examined in the light of the influence of surface monopolarity on these phenomena.

Contact angle measurements on polymer hydrogels were performed at various temperatures, and we obtained the dispersive (γ_s^d) and nondispersive (γ_s^p) components of the surface tension of polymer hydrogel at each temperature. Utilizing the temperature dependence values of γ_s^d and γ_s^p, we obtained the surface entropies of polymer hydrogels. The polymer hydrogels used were isotactic and syndiotactic poly(2-hydroxyethyl methacrylate) (HEMA), poly(2-hydroxyethyl methacrylate + aminoethyl methacrylate) (HEMA + AEMA), poly(2-hydroxyethyl methacrylate + N-vinyl pyrrolidone) (HEMA + VP), poly(2-hydroxyethyl methacrylate + methyl methacrylate) (HEMA + MMA), poly(2-hydroxyethyl methacrylate + methoxyethyl methacrylate) (HEMA + MEMA), and poly(2-hydroxyethyl methacrylate + methoxyethoxyethyl methacrylate) (HEMA + MEEMA), respectively. The contact angles were also measured by using droplets of water-immiscible liquids under conditions in which the polymer hydrogel was fully hydrated.

X-Ray photoelectron spectroscopy (XPS) was used to determine plasma induced chemical species on the surface of polyethylene (PE). Argon plasmas were found to have no detectable chemical effect on the PE surface, whereas oxygen and nitrogen plasmas created new chemical species which altered the chemical reactivity of the PE surface. Oxygen plasmas were found to react more rapidly with the PE surface than nitrogen plasmas. The degree of incorporation of new chemical species in the near surface region is approximately 20 at. % at the saturation level for both oxygen and nitrogen plasmas. Core level spectra for oxygen and nitrogen plasma treated PE suggest the formation of primarily C-O-C species in the former and C-N species in the latter. Angle-resolved XPS measurements indicate that the depth of incorporation of new chemical species is confined to the top 25 A.

We report contact angle measurements of five n-alkanes, dodecane through hexadecane, on Teflon (FEP) as a function of drop size. In all cases the contact angles decreased by approximately 5° when the drop size was increased from approximately 1 to 4 mm contact radius. A complete solution to the problem of mechanical equilibrium of a sessile drop on a solid surface indicates that the dependence of the contact angle on drop size may be explained by including the effect of line tension in the Young equation. The observed drop size dependence of the contact angle yields a line tension of (2.5 ± 0.5) × 10⁻⁶ J/m. Over the range of n-alkanes studied it was not possible to discern any dependence of the line tension on liquid surface tension.

The strength of macroscopic adhesive bonds of polymers is known to be directly proportional to the microscopic exothermic interfacial energy changes of bond formation, as measured by Dupre's 'work of adhesion'. Since the work of adhesion can be very appreciably increased by interfacial acid-base bonding with concomitant increases in adhesive bond strength, it is important to understand the acid-base character of polymers and of the surface sites of substrates or of the reinforcing fillers of polymer composites. The best known acid-base bonds are the hydrogen bonds; these are typical of acid-base bonds, with interaction energies dependent on the acidity of the hydrogen donor and on the basicity of the hydrogen acceptor. The strengths of the acidic or basic sites of polymers and of inorganic substrates can be easily determined by spectroscopic or calorimetric methods, and from this information one can start to predict the strengths of adhesive bonds. An important application of the new knowledge of interfacial acid-base bonding is the predictable enhancement of interfacial bonding accomplished by surface modification of inorganic surfaces to enhance the interfacial acid-base interactions.

A “blister test” technique has been used to determine the fracture surface energy of a range of adhesive joints formed using a polyurethane adhesive and a range of solid substrates. For each adhesive pair examined the work of adhesion was calculated from the contact angles formed by liquids for which the polar and dispersion force components of the surface tension are known. For each adhesive pair, the solubility parameter of adhesive and substrate were determined by swelling measurements in a range of liquids. Although cohesive failure of the joints was observed for some of the pairs for which the solubility parameters were matched, this was not true for all such pairs and an explanation of this behaviour has been sought in a new calculation of the volume interaction component of the molecular interaction parameters.

The recently observed enhancement in adhesion between Cu and Teflon due to a presputtering treatment of Teflon prior to the Cu deposition is analyzed. The sputtering treatment resulted in a morphology change of the Teflon, with the deposited Cu showing similar textures, and changes in chemical bondings between the two. A simple geometric model is used to analyze the contribution from the morphology changes to the observed peel strength. It is shown that, for a finite chemical bonding, an appreciable contribution to the peel strength is possible from the morphology changes observed.

The surface region of a series of $\text{poly(tetramethyl}\text{-p-}\text{silphenylenesiloxane)}\text{poly(dimethylsiloxane)}$ block copolymers was investigated using X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infra-red spectroscopy. Analysis of the results shows the surface region to be equivalent to the bulk composition for all but one sample. This indicates that for all but the most crystalline samples the surface region comprises a relatively thick layer of non-crystalline amorphous domains.

We describe a procedure to modify the surface of polyethylene (PE) film using a combination of gas discharge and wet chemical techniques. This method generates high densities (10¹⁴-10¹⁶ cm^-2) of a specific functionality, largely unaccompanied by other groups, in a 50-100-Å surface layer. The topography of the polymer surface remains unchanged after treatment and functions as an effective starting material for subsequent derivatization by standard synthetic chemical reactions. A plasma of either oxygen, water, or hydrogen is generated under comparable experimental conditions. In all cases a 1-2-s, 5-W, 0.2-Torr treatment produces about the same degree of surface modification as does longer treatment. High-resolution X-ray photoelectron spectroscopy (XPS) shows that either an oxygen or a water plasma produces a variety of oxidation products ranging from alcohols to carboxylic acids. Chromic acid oxidizes the plasma-oxidized surface further to give high densities of carboxylic acid groups which can be readily converted to acid chlorides and derivatized. Borane/tetrahydrofuran reduces the plasma-oxidized surface to give alcohols which can be esterified readily. Contact-angle measurements show that the water-plasma-treated PE surface has a higher surface free energy (γ_s ∼ 62 dyn/cm) than the oxygen-plasma-treated surface (γ_s ∼ 50 dyn/cm). A 5-s, ambient-temperature, 0.2-Torr, 2-W hydrogen plasma generates a significant number of quenchable radical sites. XPS spectra of this treated surface, exposed to either nitric oxide or nitrosotrifluoromethane, show that both compounds bond to the surface.

Results from the x-ray photoelectron spectroscopy (XPS or ESCA), ion scattering spectroscopy (ISS or LEIS), and Fourier transform infrared spectrometry (FTIR) analyses are presented for unmodified and modified poly (methylmethacrylate)/poly (methacrylic acid) (PMMA/PMAA) copolymer films. Analyses of the unmodified PMMA/PMAA copolymer series, via ESCA, ISS, and FTIR, established the surface composition and functionality of the PMMA/PMAA copolymers before the H₂O/Ar rf-plasma treatment was employed. The ESCA, ISS, and FTIR analysis of these modified PMMA/PMAA copolymers show that surface modification over a limited depth (50–200 Å) has occurred. The composition, bonding, and functionality changes of the surfaces are discussed. A two-step modification mechanism (surface reduction of the PMMA/PMAA copolymer followed by H₂O adsorption) is proposed to interpret the spectroscopic results.

Results from x-ray photoelectron spectroscopy (XPS or ESCA), low-energy ion scattering spectrometry (LEIS or ISS); and Fourier transform infrared spectroscopy (FTIR) analyses are presented for unmodified and modified poly (methylmethacrylate) (PMMA) polymer films. Analysis of the unmodified PMMA polymers (isotactic, syndiotactic, and atactic) via ESCA, ISS, and FTIR, established the surface composition, bonding, and functionality before the modification was employed. An rf-plasma glow discharge created from an Ar/H₂gas mixture at different exposure times and power levels was used to treat the polymer surface. Subsequent ESCA, ISS, and FTIR analyses of these modified PMMA's show the effects of surface modification in terms of a model of structural differences, over a limited depth (50–100 Å). The composition and functionality changes of the resulting surfaces are discussed with respect to proposed mechanisms of the plasma reaction and differences in tacticity of the reactant. A two-step reaction mechanism involving reactive decarboxylation/reduction followed by H₂O adsorption is proposed to understand the spectroscopic results.

The properties of a polymer surface can be decisive for the function of the polymer. Both in the assessment of existing polymer systems and the development of new ones the possiblity of characterizing the chemical composition and structure of the polymer surface becomes important. Various instruments and chemical methods used to characterize polymer surfaces and interfaces are reviewed. The pros and cons of electron spectroscopy for chemical analysis and derivatization schemes to enhance the detectability of functional groups, Fourier transform infrared spectroscopic methods (ATR, RIFT, PAS, micro), Raman spectroscopy, static secondary ion mass spectrometry, high resolution solid state nuclear magnetic resonance, microscopy and contact angle measurements are presented. The importance of the fact that the polymer surface can undergo comparatively rapid reorientations leading to a changed surface chemistry is discussed and exemplified.

Static secondary ion mass spectroscopy (fast atom bombardment mass spectroscopy), (SIMS (FABMS)) and Fourier transform infrared-photo-acoustic spectroscopy (FTIR-PAS) studies have been performed on samples of polypropylene subjected to different numbers of flame treatments. SIMS spectra allowed us to identify unambiguously the site of oxidation in the methyl pendant groups, because of the striking decrease in the intensity of the methyl fragment in positive-ion spectra. The behaviour of the surface concentrations of hydroxyl, formyl and carboxyl groups as a function of the number of flame treatments has also been observed, leading us to an hypothesis supporting the effectiveness of hydroxyl groups in promoting paint adhesion. FTIR-PAS spectra did not show evident changes on passing from untreated to flame-treated samples. This negative evidence is also important: it implies a limited depth of oxidation. In the light of previous XPS results and FTIR-PAS characteristics (thickness of the observed layer and sensitivity) we suggest a depth of oxidation of some 10 to 20 nm.

A study of the effects of flame treatments on a high-impact polypropylene has been performed. Both physico-chemical and mechanical properties have been investigated. The surface chemical composition has been determined by XPS, while the surface tension and the polarity were obtained through contact angle measurements. A remarkable agreement in the behaviour of chemical composition and polarity has been found, emphasizing the role of carbonyl and carboxyl groups. The adhesion of treated and untreated samples to paint coatings hua been mechanically tested. The force of adhesion remains quite constant after the first flame treatment. This suggests the importance of chemical interactions of the coating with the first layers of the polymer.