A simple but crude theoretical model involves summation of the pair potential function by integration and the use of dispersion, polar, and induction interactions for establishing the pair potential. For single-component systems the cohesive energy density, δ², the surface tension, γ, and the molar volume, V_m, are important. The theoretical model, as related to single-component systems, predicts a proportionality between δ² and $\text{γ/V}{}_{\mathrm{m}}{}^{\mathrm{<mtext>13</mtext>}}$ for molten metals and organic liquids, an increasing trend of γ with δ for polymers, and a maximum ideal tensile strength equal to about one-fourth of δ² for polymers and metals. Most of the experimental results are reasonably consistent with the theoretical predictions. For two-component interactions the model must be further modified. The δ_A or γ_A values are measures of the intensity of interactions within component A. For predicting the A–B interactions, the nature of the interactions within A and B must also be defined in terms of the fractional polarities p_A and p_B. The value of p_A can be determined either from the ionization potential, the polarizability, and the dipole moment of A or by interacting the polar material A with a nonpolar material B. The theory allows the prediction of the heat of mixing and of the ideal butt joint strength from δ_A, δ_B, p_A, and p_B and the prediction of interfacial tension from γ_A, γ_B, p_A, and p_B. While most of the available experimental data are poorly suited for exact quantitative testing of the theory, they are semiquantitatively consistent with it. The theory is useful for interpreting experimental data on polymer solubility, adhesive bond strength, wettability of polymers, and interfacial tension involving organic liquids and water or mercury. In particular, the interfacial tension between mercury and non-hydrogen-bonding organic liquids can be calculated quite accurately with the aid of the fractional polarities.

It has been found that if a film of a polymer such as polypropylene or Teflon FEP is oriented by stretching, the contact angle of liquid becomes anisotropic, being higher for liquid front advancing or retreating perpendicular to the direction of stretch than for advance or retreat in the parallel direction. Electroscanning microscopy has revealed a small degree of anisotropy of the surface roughness. Comparison with samples that have been abraded with a single stroke of abrasive paper of various grit sizes showed that a far greater degree of anisotropic roughness would be required, to produce the observed contact angle anisotropy and hysteresis, than is actually observed on the stretched samples. It is concluded that the observed contact angle anisotropy is probably due to the anisotropic force field of the oriented polymer molecules.

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.

Measurements of the interfacial tension of glycerol-dodecane, formamide-dodecane, ethylene glycol-dodecane, and aqueous ethylene glycol solution-dodecane and the surface tension of ethylene glycol-water solutions were carried out. On this basis the surface tension components of these liquids were calculated and they were compared with values from the literature. It was found that they are close to J. Panzer's (J. Colloid Interface Sci.44, 142, 1973) results obtained by using solubility parameters. In order to verify whether the determined components of the surface tension of polar liquids are valid, measurements of equilibrium contact angles for these liquids were made on the surface of paraffin, polytetrafluoroethylene, polyethylene, polyethylene terephthalate, and polymethyl methacrylate. The measured values of contact angles were compared with those calculated, using the well-known components of the surface free energy. Good agreement was achieved among measured and calculated contact angle values and those obtained by other researchers. It was found that the calculated components of the surface tension of polar liquids worked well in the studied systems, and the geometric mean used for dispersion and nondispersion interfacial interactions gives good results despite existing intermolecular forces due to hydrogen bonding.

Employing the values of organic liquid surface tension and interfacial surface tension of water-organic liquid, values of dispersion and nondispersion components of these liquids were calculated and compared with those obtained in another way. For these organic liquids and water, the values of the contact angle on paraffin wax, polytetrafluoroethylene, polyethylene, polyethylene terephthalate, and polymethyl methacrylate were measured. The values of dispersion and nondispersion components of surface free energy of these polymers and paraffin wax were calculated using the measured values of the contact angle for diiodomethane and water and the calculated values of the components of their surface tension. These calculated data were in agreement with the literature data. Taking our values of free energy components of liquids and solids, the values of the contact angle for these solids were calculated and compared with those measured, obtaining good agreement. On the basis of the measurements and calculations it was found that dispersion and nondispersion components of surface free energy of liquids and solids “work well” in the systems studied.

Using the literature data of the refractive index, the structural unit molar volume of polymers and their dipole moment, as well as the literature data of the polarizability, ionization potential, and dipole moment of many liquids, values of the Φ parameter for paraffin—liquid and polymer—liquid interfaces were calculated. Next, introducing these values of Φ and the earlier measured values of the contact angle for many liquids to the Young equation, values of the surface free energy (γ_S) of paraffin, polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene terephthalate (PET), and polymethacrylate (PMMA), were determined. It was found that the average values of γ_S for these solids were in agreement with those calculated on the basis of geometric, harmonic, or harmonic—geometric mean approaches. The values of the surface free energy of paraffin, PTFE, PE, PET, and PMMA were also calculated from the Young equation modified by Neumann et al. and, using the earlier measured values of the contact angle for many liquids, they were compared with the values obtained by other methods. Next, employing the mean value of the surface free energy, values of the contact angles for many liquids were calculated and compared with those measured earlier for the same liquids. It was found that for paraffin, PTFE, and PE there were big differences among the values of their surface free energies calculated from the contact angles for some liquids; however, the average values were in agreement with those obtained by other methods. The average values of the surface free energies of PET and PMMA were also in the range of the results obtained by other authors. It was also found that the average deviations of the contact angles calculated from the Young equation modified by Neumann et al. from the measured ones were slightly larger than those of the contact angles calculated from equations employing the geometric and harmonic means of the surface free energy components; the method of Neumann et al. may also be used to predict the wettability in some systems.

Polymeric solid surfaces were prepared by a radiation-induced graft copolymerization technique using various mixtures of 2-hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA). Low-density polyethylene (PE) films were used as graft substrates. Contact angles on these polymeric surfaces were determined in air and under water. The critical surface tension (γ_c) of each polymeric surface in air was estimated by the Zisman method. Geometric mean and harmonic mean approximation methods were utilized to estimate the dispersion force contribution (γ_s^d) and the polar contribution (γ_s^p) to the total surface free energy (γ_s) from contact angle data in air. The geometric mean approximation was also used to estimate γ_s^d′ and γ_s^p′ from contact angles under water. The calculated values of γ_s^d, γ_s^p are strongly dependent on the pair of liquids chosen for the calculation regardless of the approximation adopted. The values of γ_s, calculated as the sum of γ_s^d and γ_s^p, are close to the γ_c values and are less dependent on the pair of liquids used. A comparison of the ratio γ_s^d/γ_s^p for the same surface in air and under water suggests that major polymer chain conformational changes occur, particularly with respect to the hydroxyl side chain, when such surfaces are immersed in water.

A thermodynamic model is used to predict the adsorption of nonionic surfactants on latexes with different polarity. The model, which is based upon the Flory-Huggins theory of polymer solutions, predicts that the adsorption decreases as the polarity of the latex increases. It is predicted that adsorption should occur even when it is unfavorable to replace a surface-water contact with a surfacesurfactant contact. This is due to a lower number of unfavorable hydrocarbon-water contacts when the surfactant is adsorbed, compared to when it is free in solution. It is also predicted that it is in principle possible to determine the latex polarity or solubility parameter, from adsorption measurements, provided that a similar experiment is carried out on a latex with known polarity, or solubility parameter.

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.

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.

PTFE was treated with oxygen plasma, and the effects of treatment time were evaluated by XPS, SEM, and the contact angles of water and CH₂l₂. Advancing and receding angles were interpreted in the light of current theories on contact angle hysteresis. It was found that at short treatment time wettability reflects chemical modification of the surface, while at longer treatment times surfaces are deeply etched and contact angles are controlled by roughness. With water as the wetting liquid, the typical behavior of composite surfaces was observed.

Oxygen plasma-treated polydimethylsiloxane surfaces were aged in a low-energy (air) and in a high-energy (water) medium. Treated samples were characterized using a combination of surface-sensitive techniques: X-ray photoelectron spectroscopy, static secondary ion mass spectroscopy, and contact angle measurements. Plasma treatments cause large increases in surface tension of treated samples. When aged in air (low-surface-energy medium) the samples returned to a low-surface-tension situation. The mechanism was a combination of diffusive burial of polar groups in the bulk and condensation of silanol groups formed by plasma treatment and consequent crosslinking. When aging was performed in water, a high surface tension was maintained.

An equation of state is developed which allows the surface tension of a low-energy solid to be determined from a single contact angle formed by a liquid which is chemically inert with respect to the solid and whose liquid surface tension is known. The equation of state is obtained using two independent methods. In the first one, similar arguments to those in previous papers are used; however, the qualitative argument, based on the general appearance of plots, is replaced by computer curve fitting and statistical analysis. The second method, which has not been employed heretofore, treats the solid surface tension as an adjustable parameter. Molecular arguments in conjunction with the interaction parameter Φ are used to eliminate poor choices of the solid surface tension. The results are in excellent agreement with the first method.

The range of validity of the equation of state and practical points in its application are discussed.

The use of scanning electron microscopy for direct observation of the effects of surface roughness on the spreading of liquids is described, making it possible to view moving liquid drops at distances less than 1 μm from the advancing contact line. Various surfaces were examined including several with simple forms of roughness which can assist in explaining the behavior of more complex surfaces. Spreading is shown to be highly dependent on the orientation and texture of the roughness; in particular, the presence of sharp edges of step height ⩽0.05 μm are shown to influence spreading significantly. These observations reinforce our previously stated doubts of the significance of conventionally measured macroscopic contact angles.

Polystyrene tissue culture vessels are commercially treated by corona discharge or plasma surface oxidation to provide a hydrophilic surface, with 15–20% surface oxygen. ESCA and FTIR showed that oxidation forms hydroxyl, carbonyl, and carboxyl groups. We have discovered that water washing removes about half the oxidized species. It is believed that reaction with the vinyl polymer backbone to form carboxyl groups results in CC bond scission to form soluble fragments; addition and ring reactions would not yield soluble species. This functional group removal could affect the desired properties, such as the use of these groups as anchors in chemical coupling.

Three methods of manipulating wetting data appear satisfactory in providing estimates of the components of solid surface free energy due to dispersion, Keesom, and hydrogen-bonding forces. These include: an extension of the Hansen method with contact angle data, which had been applied to solubility parameters, to surface free energy calculations; Hansen plots of absorption volume data; and Zisman plots using the components of surface tension rather than total surface tension. The Fowkes equation for the dispersion component of surface free energy agrees well with the results from the empirical methods. Extensions and modifications of the Fowkes equation to provide the polar components of solid surface free energy have not worked well when evaluated with a wide range of reference liquids.

The effect of velocity upon the advancing and receding contact angles of water, glycerol, formamide and methylene iodide on glass coated with a dimethyl siloxane layer has been investigated. The cosines of the dynamic contact angles of water and glycerol vary linearly with the interfacial velocity, as predicted by hydrodynamic theory. However, this treatment cannot account for the magnitudes of the velocity effects observed with water and glycerol. Qualitative molecular considerations explain certain features of the velocity dependence of advancing contact angles. Initial rapid relaxation of the contact angles occurs on removal of the drive because of molecular reorientation of liquid molecules at the solid interface. There are further slow changes of water and methylene iodide advancing contact angles with time because of penetration of liquid changing the solid-liquid interfacial tensions. No penetration occurs with glycerol and formamide because of their greater effective molar volumes and with the former liquid the advancing and receding angles relax to a common value of about 90° which is considered to be the equilibrium value.

The relationships of the optical characteristics of monomers (refractive index and specific refraction) and the cohesion parameters of polymers (effective cohesional energy and molar volume of the repeating unit) have been analyzed. New relationships are proposed that allow the calculation of the surface energies of homo- and copolymers using refractometric data of monomers. The relationships were tested with good consistency for a number of polymers of various chemical nature.

In forced spreading systems, three different modes of θ_d-V behavior have been found, each of which predominates in a different velocity range. In the lowest velocity range, with systems involving the low viscosity, low boiling, nonpolar liquid hexane, θ_d was found equal to θ_eq (the Elliott-Riddiford or Hansen-Miotto mode). In the next higher velocity range, which extends to very low velocities for all other systems studied, the behavior described by Eq. 6 (the Blake-Haynes mode) predominates. At still higher velocities, the behavior described by Eq. [9] (the Friz mode) becomes superposed on the Blake-Haynes mode, and eventually predominates up to the range where θ_d approaches 90° and Eq. [9] becomes inapplicable. In the Blake-Haynes mode the major force opposing advance of the liquid front is the solid-liquid interfacial viscosity. In the Friz mode it is the bulk viscosity of the liquid.

The roughness of solid surfaces has no appreciable effect on the θ_d-V relationship, provided the physicochemical character of the surfaces is the same and the roughness is random. If the process of roughening alters the physicochemical character the θ_d-V behavior of the roughened surface may differ from that of the smooth one.

There is no qualitative difference between the θ_d-V behavior of systems in which θ_eq is zero and systems in which θ_eq is positive.

The surface structure and properties of poly(vinyl alcohol)-poly(dimethylsiloxane), PVAL-PDMS, graft copolymers with the controlled PDMS graft chain length as well as chain distribution were studied. The surface of the graft copolymer was examined by XPS technique and was found to be covered with essentially pure PDMS graft component even in only 5 mole% siloxane unit content. The contact angle measurement was carried out with the water-in-air technique for PVAL—PDMS graft copolymers as well as the graft copolymer/PVAL homopolymer blends and the significant surface accumulation of PDMS graft component was confirmed with the graft copolymer/PVAL blend of less than 1 mole% of siloxane unit content. In contact with water, PVAL—PDMS graft copolymer surface was found to transform its surface morphology remarkably, which was noticed by the contact angle measurement with the air-in-water technique, where the contact angle of PVAL—PDMS graft copolymer surface was found to differ from that of pure PDMS—coated surface.

Contact angle hysteresis was measured for a variety of liquids on condensed monolayers of 17-(perfluoroheptyl)heptadecanoic acid adsorbed on polished chromium. The hysteresis was shown to be simply related to the molecular volume of the liquid and to result from the penetration of liquid molecules into the porous monolayer. However, contact angle hysteresis was negligible when the average diameter of the liquid molecules was larger than the average cross-sectional diameter of the intermolecular pores. It is shown that it is possible to estimate intermolecular pore dimensions of such adsorbed monolayers by contact angle hysteresis measurements on a series of liquids having gradations in molecular volume. The results of this investigation reveal that liquid penetration, even into pores of molecular dimensions, is a cause of significant contact angle hysteresis, and it is also shown how liquids can be selected for contact angle investigations on organic solid surfaces so that there will be freedom from this source of hysteresis. The results also suggest that under these experimental conditions, liquid water, on the average, behaves as if it were associated in clusters of about six water molecules. Similarly, both ethylene glycol and glycerol behave as associated clusters of about two molecules.

The contact angle of water on several polymer films was determined by three different methods; telescopic sessile drop, laser beam goniometry, and the Wilhelmy plate technique. The telescopic sessile drop method is the simplest, but the least accurate; whereas the laser beam goniometry compares favorably with the Wilhelmy plate in terms of accuracy, but cannot easily provide information on contact angle hysteresis.

The thermodynamic nature of interfaces and of adhesion is reexamined in the light of the Lifshitz theory of the forces acting across condensed phases. A new term is proposed, γ^LW, which consists of the sum of the terms heretofore ascribed to London, Debye, and Keesom forces, LW referring to Lifshitz-van der Waals. This term and a second term γ^SR account for the entirety of two-phase interactions in nonionic systems; SR refers to short range forces. This new analysis of forces is of value in explaining some important biological and other phenomena. The rather strong attachment of hydrophilic proteins, e.g., human serum albumin (HSA) and human immunoglobulin G (IgG), to low energy surfaces, e.g., polytetrafluoroethylene (PTFE) and polystyrene (PST), while immersed in H₂O, cannot be ascribed solely to Lifshitz-van der Waals forces (LW). For instance, it can be shown that the LW interaction would give rise to a repulsion between HSA and PTFE. The short range (SR) interactions, e.g., between H₂O and HSA, are due to H-bonds, which cannot directly account for interactions with PTFE. However, the combined SR interfacial tensions between the H-bonding liquid, the biopolymer, and the low energy surface still result in a strong attraction between PTFE and HSA, immersed in H₂O. This is analogous to the behavior of a liquid-air interface (where the fact that the direct interaction between a given solute and air is zero does not preclude the solute from being preferentially attracted to the interface). This SR attraction (minus the LW repulsion) between HSA and PTFE, in H₂O, is of the same order of magnitude as the adsorption energy derived from the Langmuir isotherm obtained for this system. Analogous results are found with IgG and PTFE, and also with HSA and IgG, with PST. Desorption patterns (obtained by changing the γ^LW and γ^SR of the liquid medium) allow an insight into the degree of local dehydration (or “denaturation”) of adsorbed proteins under various conditions. It is suggested that the term interfacial forces more aptly describes the underlying mechanism than “hydrophobic interactions.”

Low-temperature radiofrequency excited gas plasma was applied to the surfaces of a number of polymers. Polymers that are known to crosslink as well as those that only degrade under irradiation were included in the investigation. Surface changes were studied by viscosity, gel content, and contact-angle measurements. Changes in adhesive bond strength were used as a measure of overall practical effects of plasma treatment. In each case the response of the polymer surface to an oxidizing (oxygen) and a nonoxidizing (helium) plasma environment is discussed. Further indications of the nature of the surface changes were suggested by statistical treatment of the bond-strength data.

The paper presents a theory on determining the dynamic surface tension using two methods: the drop volume method and the maximum bubble pressure method.

The problem of the deformation of a quiescent air/liquid interface by a plunging solid surface is considered in the context of a differential force balance of the type used in withdrawal theory. Interfacial deformation and air entrainment which eventually arises at high speeds are discussed in terms of three separate regions: where the dynamic contact angle, θ, is >90°, 90° > θ > 180°, and θ → 180°. This latter condition leads to the development of a dimensionless correlation between Weber and Bond numbers correlating air entrainment data which were found to be in substantial agreement with the experimental results. The theoretical and experimentally measured profiles also showed good agreement, particularly for viscosities up to 6.77 P and dynamic contact angles less than 180°, for surface tensions in the range 34 < π < 65 dyn·cm⁻¹.

In the conventional methods of estimating the wetting characteristics of solids from contact angle experiments, the surface energetic properties of the solid are assumed to be identical in the environments of both the surrounding medium and probe fluids. While this assumption is suitable for solids which possess rigid surface structures (such as glasses, ceramics, and metals for example), it is generally inapplicable to polymeric solids, since the surfaces of the latter are relatively mobile so as to be able to adopt considerably different configurations in different environments. Based on a recognition of this feature of polymeric surfaces, a sequence of contact angle experiments is suggested to estimate: (a) the instantaneous as well as equilibrium surface energetic properties of a polymeric solid in an aqueous environment and (b) the time required for the polymeric surface to attain its equilibrium wetting characteristics in the aqueous environment. In order to illustrate the applicability of the suggested contact angle procedure, it is necessary to prepare model polymeric surfaces, which are smooth in surface texture, nonporous, and also chemically homogeneous. Such model surfaces were prepared in this study, by radio frequency sputter deposition of thin solid films of oxidized fluorocarbon compounds (from a Teflon FEP target) onto the smooth surfaces of highly polished, single crystal silicon substrates. The estimation of the wetting characteristics of the sputtered polymer films in an aqueous environment was then carried out by the suggested contact angle procedure. The results of the contact angle experiments indicate that the solid-water interfacial free energy of the sputtered polymer film which was initially equilibrated in an octane environment, decreases from an instantaneous value of 50.88 dyn/cm to an equilibrium value of 26.59 dyn/cm, over a duration of about 24 h. Such a change in the solid-water interfacial free energy of these model polymeric surfaces can arise due to a time-dependent reorientation of the buried polar groups of the solid from its bulk to its surface, when it is placed in contact with a strongly polar liquid like water. This interpretation was found to be consistent with the results of ESCA characterization, which indicated that the outer surface layers of the sputtered polymeric specimen contained a fair amount of the polar oxygen atoms that are capable of reorienting themselves from either the interior of the solid to its surface or vice versa, depending on their surrounding environment.

A method for measuring the dispersive part of the surface free energy γs^D of a high-energy solid, and its interaction energy with water and n-alkanes, W_SL, has been developed. It is based on the measurement of the contact angle of water on the solid under n-alkanes. Muscovite mica was chosen as a model high surface energy solid. The results obtained for γs^D and W_SL of mica are in good agreement with the results obtained by other techniques. The present method can be considered to be applicable for other solids.

A method of determining the polar term of the adhesion energy of several liquids to a high-energy solid, I_SL^P, has been developed, based on the measurement of the contact angle of water on a solid in a liquid medium. The I_SL^P values for mica are found to be a linear function of the square root of the polar term of the surface free energy of liquids. This finding agrees with the suggestion that the polar term of the energy of adhesion may be represented by the geometric mean of the polar term of the surface free energy of a solid and a liquid. The slope of the straight line provides the value of γ_S^P = 90 ergs/cm² for the polar term of the surface free energy of mica. The results were compared with those obtained by a cleavage method and also discussed in terms of each component of the surface free energy of mica. The present method is useful for the determination of the polar part of the energy of adhesion of a high-energy solid to liquids, and its surface free energy.

The surface free energy of polymeric films of polyvinylchloride (PVC) + poly(ethylene-co-vinylacetate) (EVA) blends was calculated using the van Oss treatment (Lifshitz and electron donor–electron acceptor components of surface free energy) and the Owens–Wendt treatment (dispersive and nondispersive components of surface free energy). Surface free energy results were found to be greatly dependent on the calculation method and on the number of standard liquids used for contact angle measurements. The nondispersive/donor–acceptor surface free energy component and the total surface free energy of polymeric films were always higher when the van Oss treatment was used compared to the Owens–Wendt treatment. Conversely, both methods led to similar apolar/Lifshitz components. All the calculation methods were in good agreement for the surface free energy of PVC; however, a discrepancy between the methods arose as EVA content in the blends increased. It seems that there is not yet a definite solution for the calculation of solid surface free energy. Further developments of existing models are needed in order to gain consistency when calculating this important physicochemical quantity.

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.

Several thermoplastic (technical, engineering, and high-performance) polymers were characterized using contact angle and electrokinetic measurements. From the measured contact angles of various test liquids on polymers, we calculated the solid surface tensions using the different approaches to determine them and compared the results. Zeta (ζ)-potential measurements gave information about the swelling behavior of the polymers in water, the surface chemistry, and the interactions with dissolved potassium and chloride ions. All investigated polymers displayed an acidic surface character. Comparing the results obtained from the ζ-potential measurements with the acid-parameter of the surface tension γ⁺ calculated from the measured “static” contact angles using the van Oss, Good, and Chaudhury approach revealed the same tendency. The correctness of the acid–base approach regarding the “overall” chemical surface character could be shown. However, it seems that the basic parameter γ⁻ obtained from the acid–base is greatly overestimated.

By means of an equation containing two adjustable coefficients it is possible to relate the surface free energy to the energy of vaporization, using the Hansen parameters from London force energy, polar energy, and hydrogen-bonding energy. The technique is applicable to simple organic liquids, mixtures of simple liquids, and most liquid metals. Hydroxy compounds, acidic and basic organic liquids, certain hexagonal and irregular metals, and most fused halides require special versions of the basic equation.