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91. Eick, J.D., R.J. Good, and A.W. Neumann, “Thermodynamics of contact angles, II. Rough solid surfaces,” J. Colloid and Interface Science, 53, 235-248, (1975).

The thermodynamics of an idealized rough surface is treated, using the geometry of a vertical plate partially immersed in a liquid. Gravity is included explicitly in the theory. The results of this treatment are more general than those of previous studies and are more easily extended to other surface topographies. Some novel results are found, such as a delineation of the conditions under which a macroscopic contact angle of 180° will result from geometric properties of the solid surface. On rough surfaces consisting of material for which, if smooth, the equilibrium contact angle would be different from 90°, the slopes of the asperities will be a very important factor in determining the effective equilibrium contact angles.

2363. Osterholtz, F.D., “Low energy electron beam treatment of polymeric films, and apparatus therefor,” U.S. Patent 3846521, Nov 1974.

1831. Tadros, M.E., P. Hu, and A.W. Adamson, “Adsorption and contact angle studies I: Water on smooth carbon, linear polyethylene, and stearic-acid coated copper,” J. Colloid and Interface Science, 49, 184-195, (Nov 1974).

Ellipsometrically determined adsorption isotherms are reported for water on two types of pyrolytic carbon, on polyethylene, and on stearic acid-coated copper, for relative pressures up to close to the saturation pressure, P0, and for various temperatures. Contact angle data for bulk water on the same solids are included; advancing angles of 60°–90° were found. The adsorbed film thickness reaches 40–80 Å in the first two systems, but only a few angstroms in the second two; correspondingly, the surface pressures of P0, π0, are large in the first two cases and small in the second two. Large contact angle thus does not necessarily imply low π0. The data are fitted to a previously published potential-distortion model, which allows adsorption and contact angle behavior to be related.

2003. Toyama, M., and T. Ito, “Studies on surface wettability of stereoscopic poly(methacrylic acid esters),” J. Colloid and Interface Science, 49, 139-142, (Oct 1974).

The wettability of stereospecific poly(methacrylates) was studied. In the wettability of poly(methacrylates) having bulky substituents such as phenyl and chloroethyl groups, it was found that the critical surface tensions for isotactic polymers were low compared to those for attactic polymers. The steric effect of the bulky substituent on wetting was also discussed.

1791. El-shimi, A., and E.D. Goddard, “Wettability of some low energy surfaces I: Air/liquid/solid interface,” J. Colloid and Interface Science, 48, 242-248, (Aug 1974).

The wettability of a number of low energy solid surfaces, including hoof keratin and human skin, has been examined using two liquids, water and methylene iodide, and employing Wu's empirical approach to obtain γsd and γsP, the dispersion and polar components of the solid “surface tension.” The sum of these parameters, (γsd + γsp) was found to be in good agreement with reported values of γc, the critical surface tension, based on Zisman plots. Using the latter method, γc values of solids selected from the above group were determined using aqueous ethanol solutions. The values were lower than those obtained using nonpolar liquids, thus confirming earlier findings. A compilation of our own data and data from the literature reveals that the derived values of γc show little or no dependence on the type of solid surface, the type of alcohol or its chain length. The results can be explained in terms of adsorption of alcohol at the surface of the solid.

2004. Hamilton, W.C., “Measurement of the polar force contribution to adhesive bonding,” J. Colloid and Interface Science, 47, 672-675, (Jun 1974).

The dispersion force contributions to the surface free energies of octane and water are equal—21.8 dyn/cm. Octane's surface free energy has no polar component, whereas water has a polar contribution of 50.2 dyn/cm. Therefore, the increase in the contact angle of octane on various polar polymer surfaces underwater is a quantitative measure of the interfacial stabilization energy from polar forces. Octane contact angles were measured underwater on polyethylene, polytetrafluoroethylene, and polyethyleneglycolterephthalate surfaces before and after surface oxidation in a low temperature asher. The octane contact angles increased in each case as the surfaces became oxidized. When simple lap joints were prepared from these polymers and then broken in an Instron Tester, the measured breaking forces correlated well with the octane contact angles. Breaking strength increases of 1.1, 1.2, and 1.8 psi were realized with the polyethylene, polytetrafluoroethylene, and polyethyleneglycolterephthalate, respectively, when the polar forces were increased by 1 erg/cm2.

2816. Dynes, P.J., and D.H. Kaelble, “Surface energy analysis of carbon fibers and films,” J. Adhesion, 6, 195-206, (1974).

Amorphous and graphitic carbon fibers and film surfaces are characterized by wettability measurements and surface energy analysis which isolate the (London-d) dispersion γd svand (Keesom-p) polar γp sv contribution to solid-vapor surface tension γsvd sv + γp sv Graphitized carbon fibers which are surface treated to provide strong bonding to polar matrix resins show consistent strong polar contributions to total surface tension with γd svsv ≃ γp svsv ≃ 0.50. Amorphous carbon films prepared for biological implant applications display dominant dispersion character in surface energy with γd svsv ≃ 0-74 to 0.95 and γp svsv ≃ 0.05 to 0.24.

2334. Hudis, M., “Plasma treatment of solid materials,” in Techniques and Applications of Plasma Chemistry, J.R. Hollahan and A.T. Bell, eds., 113-147, John Wiley & Sons, 1974.

1842. Toyama, M., A. Watanabe, and T. Ito, “Surface wettability of alkyl methacrylate polymers and copolymers (letter),” J. Colloid and Interface Science, 47, 802-803, (1974).

608. Zorll, U., “Significance and problem of the critical surface tension,” Adhesion, 18, 262+, (1974).

506. Kloubek, J., “Interaction of polar forces and their contribution to the work of adhesion,” J. Adhesion, 6, 293+, (1974).

It is shown that the best fit of experimental data to the correlation equation as used by Fowkes1 cannot be considered as a criterion of correctness with which the mathematical formula expresses the way of polar interaction at interfaces. Examples of other evidence are given that the polar part of work of adhesion may be well represented by the geometrical mean of polar components of surface energies.

498. Kaelble, D.H., P.J. Dynes, and L. Maus, “Surface energy analysis of treated graphite fibers,” J. Adhesion, 6, 239+, (1974).

Wettability measurements and surface energy analysis are applied to isolate the (London-d) and (Keesom-p) polar contributions to solid-vapor surface tension γsvd sv + γp sv of surface treated graphite fibers. Surface treatments include metal coatings with Al, Cu, and Ni, chemically reducing heat treatments in H2 and vacuum, and films of highly chlorinated polymers such as polyhexachlorobutadiene and polychloral. This study shows that the highly polar surface properties γp svsv ≃ γd svsv ≃ 0.50 of commercial graphite fibers can be modified by surface treatment to display dominant dispersion character with γd svsv ≃ 0.79 to 0.92 without substantial reduction in total surface energy γsv. For adsorption bonded fiber/matrix interfaces a new method of mapping the surface energy effects of an immersion phase upon the Griffith fracture energy γG is applied to define criteria for strong interfacial bonding under both air and water immersion.

393. Wu, S., “Interfacial and surface tensions of polymers,” J. Macromolecular Science, C10, 1-73, (1974).

Interfacial and surface tensions of polymers are important in the technology of plastics, coatings, textiles, films, and adhesives through their roles in the processes of wetting, adsorption, and adhesion. Because of experimental difficulty due to high viscosity, however, reliable measurements of these quantities were not reported until 1965 for surface tensions [l, 2] and 1969 for interfacial tensions [3, 4]. A body of scattered data has been accumulated in the literature. This review will evaluate, compile, and interpret these results.

385. Westerdahl, C.A.L., J.R. Hall, E.C. Schramm, and D.W. Levi, “Gas plasma effects on polymer surfaces,” J. Colloid and Interface Science, 47, 610-620, (1974).

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.

324. Schonhorn, H., and F.W. Ryan, “Surface crosslinking of polyethylene and adhesive joint strength,” J. Applied Polymer Science, 18, 235-243, (1974).

Exposure of polyethylene film to UV radiation at wavelengths of ≤2537 Å is sufficient to induce surface crosslinking and to facilitate the formation of strong adhesive joints to these surfaces with conventional adhesives. Reduction of the vapor pressure in the reaction vessel to about 1 torr apparently maximizes the efficiency of the crosslinking process. Examination of the treated films which have been exposed for times necessary to form strong adhesive joints has revealed an absence of surface oxidation. It appears that crosslinking to improve the mechanical strength of the surface region of the polyethylene is sufficient to allow the formation of strong adhesive joints.

255. Neumann, A.W., R.J. Good, C.J. Hope, and M. Sejpal, “An equation-of-state approach to determine the surface tensions of low-energy solids from contact angles,” J. Colloid and Interface Science, 49, 291-304, (1974).

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.

87. Dwight, D.W., and W.M. Riggs, “Fluoropolymer surface studies,” J. Colloid and Interface Science, 47, 650-660, (1974).

By combining four techniques—X-ray photoelectron spectroscopy (ESCA), soft X-ray spectroscopy, contact-angle hysteresis, and electron microscopy—a powerful method to elucidate the nature of solid surfaces is created. ESCA provides semiquantitative elemental analysis of the uppermost 5–100 Å of the sample. Soft X-ray spectroscopy extends the elemental analysis to a depth of about a micron. Contact-angle measurements can be interpreted in terms of the distribution of surface energy and roughness, and a view of the microtopography is obtained with the electron microscope. This method of surface characterization has been applied to several problems in fluoropolymer surface chemistry. For example, certain sodium complex solutions are shown to react with fluoropolymer surfaces, removing most of the fluorine and leaving a sponge-like surface with characteristics of an unsaturated, oxidized hydrocarbon. Also analyzed are surface changes that occur upon exposure of these sodium-etched films to environmental conditions. In another application, films of poly(tetrafluorethylene/hexafluoropropylene) melted and recrystallized against a gold substrate were analyzed. The unusual wettability of such films has been attributed to the presence of a “transcrystalline” surface region, but our analysis indicates the presence at the surface of a very thin layer of materials with the characteristics of an oxidized hydrocarbon. The increased wettability is evidently due to the presence of this layer.

24. Blais, P., D.J. Carlsson, G.W. Csullog, and D.M. Wiles, “The chromic acid etching of polyolefin surfaces, and adhesive bonding,” J. Colloid and Interface Science, 47, 636-649, (1974).

Chromic acid solutions were used to oxidatively etch linear (high density) and branched (low density) polyethylene and isotactic polypropylene. Etched surfaces were characterized by surface IR spectroscopy, wettability, electron microscopy and aqueous adhesive bonding (peel test). Polypropylene was found to etch rapidly, but showed little residual chemical or topographical change. The polyethylenes etched more slowly, especially in the case of the linear polymer, but showed large changes in surface chemistry as a result of oxidative attack. Adhesion onto polyolefin films and fabric increased very rapidly during the first few seconds of attack. This increase is interpreted in terms of wettability, topography and cohesive strength of the surface layer. The differences in etch behavior between the polyolefins is interpreted in terms of ease of oxidative attack at branch points, and surface accessibility to the acid.

2. Baszkin, A., and L. Ter-Minassian-Saraga, “Effect of temperature on the wettability of oxidized polyethylene films (letter),” Polymer, 15, 759-760, (1974).

3029. O'Kane, D.F., and K.L. Mittal, “Plasma cleaning of metal surfaces,” J. Vacuum Science and Technology, 11, 567-569, (1974).

Mild plasma cleaning of metal surfaces was shown to be effective in removing organic contaminants. Auger electron spectroscopy and surface wettability measurements were used to evaluate the plasma cleaning procedure and to provide a comparison with conventional solvent cleaning methods.

2362. Osman, M.S., “Electrode for sheet material surface,” U.S. Patent 3777164, Dec 1973.

823. Toyama, M., T. Ito, H. Nukatsuka, and M. Ikeda, “Studies on tack of pressure-sensitive adhesive tapes: On the relationship between pressure-sensitive adhesion and surface energy of adherents,” J. Applied Polymer Science, 17, 3495-3502, (Nov 1973).

The relationship between wetting and pressure-sensitive adhesion was studied using an adhesive composed of poly(butyl acrylate) and various adherends of different surface tension. The amount of adhesive deposit was determined quantitatively by tracer technique although the unbonding process was apparently observed as interface failure. The adhesive force and amount of deposit were both dependent on the critical surface tension of the adherends. Maximum tack value and contamination were observed with adherends whose critical surface tension was close to that but a little higher than that of the adhesive. The adhesive force obtained was lower than cohesive strength of adhesive. From this evidence, a mechanism for pressure-sensitive adhesion was discussed: the bond breaks in the addesive mass around the very minute spots where interaction is at work between adhesive and adherend. Inasmuch as the density of the minute spots per unit area depends on the surface tension, the adhesive force also depends on the surface tension.

2006. Good, W.R., “A comparison of contact angle interpretations,” J. Colloid and Interface Science, 44, 63-71, (Jul 1973).

Three methods of interpretation of contact angles in terms of surface tension of liquid and solid are correlated. It is shown that the critical surface tension for wetting γc is dependant in a specific way on the nature of the liquid system used regardless of the nature of the solid. Equations are derived which express the limiting values γc may assume for a liquid/solid system. γc is also correlated with the Good-Girifalco treatment of contact angles and experimentally determined values of the parameter φ are compared with theoretical calculations from molar volumes of normal alcohol-paraffin wax interfaces.

The Fowkes method of contact angle interpretation is used to derive values for the polar and dispersion force components of liquid surface tensions for three alcohol/water solution series and two organic acid/water solutions.

2005. Rhee, S.K., “Surface tension of low-energy solids,” J. Colloid and Interface Science, 44, 173-174, (Jul 1973).

2007. Baszkin, A., and L. Ter Minassian-Saraga, “Wetting of polyethylene by water, methylene iodide and methylene iodide-decalin mixtures,” J. Colloid and Interface Science, 43, 190-202, (Apr 1973).

The wettability of oxidized polyethylene films was studied with pure liquids (water and methylene iodide) and practically nonpolar mixtures of Decalin and methylene iodide. A linear variation was found of the wettability of these films with the chemical composition of their surfaces (determined by adsorption of radioactive 45Ca ions).

A value of γsd for the polyethylene was found with the nonpolar mixtures of methylene iodide and Decalin and the values of the solid-liquid polar interactions (IslP) for oxidized polyethylene were deduced.

Dipole-dipole and induced dipole-dipole interactions between the pure liquids and the oxidized and unoxidized polyethylene were calculated for two possible orientations of the hydrocarbon chains to the surface and compared with the experimental results. Generally a poor agreement was obtained, mainly due to the difficulty in estimating the correct values for the distances between molecules or groups. However, a better agreement was obtained assuming that the chains were perpendicular to the surface.

1979. Evans, J.M., “Nitrogen corona activation of polyethylene,” J. Adhesion, 5, 1-7, (Jan 1973).

Experiment has shown that the nitrogen corona-induced autohesion of polyethylene and the nitrogen-corona induced sorption of iodine by polyethylene both follow similar mechanisms. The controlling factor is postulated to be the formation of short-lived electrets within the polymer surface.

1978. Evans, J.M., “The influence of oxygen on the nitrogen corona treatment of polyolefins,” J. Adhesion, 5, 9-16, (Jan 1973).

The resultant surface activation of polymers by corona discharges has been found to be markedly influenced by the type and purity of gases used in the corona. In this work it is shown that for the nitrogen gas corona treatment (15 KV, 15 mins) of polyethylene and polypropylene, traces of oxygen, >0.5% and <0.15% respectively, are sufficient to produce chemical changes in the polymer surface.

2331. Gent, A.N., and J. Schultz, “Effect of wetting liquids on the strength of adhesion of visoelastic materials,” J. Adhesion, 3, 281-294, (1973) (also in Recent Advances in Adhesion, L.-H. Lee, ed., Gordon and Breach, p. 253-268, 1973).

The effect of a variety of wetting liquids on the resistance to peeling separation for a lightly crosslinked rubbery adhesive in contact with a Mylar substrate has been studied over a wide range of peeling rates and at two temperatures. Although the magnitude of the peel strength is much greater than the thermodynamic work of detachment, it is reduced by alcohols and alcohol/water mixtures in good agreement with calculated reduction factors. It is concluded that the measured strength is a product of two terms: the thermodynamic work, and a numerical factor, generally large, denoting inefficiency. The latter term is strongly dependent on peel rate and temperature for viscoelastic adhesives. Two anomalies are pointed out: particularly low adhesion is observed at low rates of peel for certain liquids, attributed to swelling of the adhesive, and smaller effects are found for some other liquids than predicted.

2329. Wu, S., “Polar and nonpolar interactions in adhesion,” J. Adhesion, 5, 39-55, (1973) (also in Recent Advances in Adhesion, L.-H. Lee, ed., Gordon and Breach, p. 45-63, 1973).

Equations for polar and nonpolar interactions across the interface are developed by using energy additivity concept in a semi-continuum model. Interfacial and surface tensions of molten polymers are measured directly and used to test the resulting equations: The first expression may be called the harmonic-mean equation preferred for low energy systems such as organic liquids, water, polymers, and organic pigments. The second may be called the geometric-harmonic-mean equation preferred for high energy systems such as mercury, glass, metal oxides and graphite. The third may be called the geometric mean equation which is found unsatisfactory. The harmonic-mean equation is used to obtain the “optimum” wettability condition for adhesion. The importance of polar interactions and matching of the polarity are analyzed and emphasized.

1779. Andrews, E.H., and A.J. Kinloch, “Mechanics of adhesion failure,” Proceedings of the Royal Society of London, A332, 385-399, (1973).

The mechanics of adhesion have been investigated both theoretically and experimentally, using model adhesive joints consisting of a crosslinked amorphous rubber bonded to a variety of rigid polymeric substrates.

An adhesive failure energy, θ, is defined which is characteristic of the bond but independent of test-piece geometry. Both theory and experiment show that θ has the form, θ=θ0f(R) where θ0 is the “intrinsic adhesive failure energy” which depends only on the physical and chemical nature of the adhesive-substrate interface, and f is a function of R, the “reduced” rate of failure propagation obtained from rate and temperature data using the WLF equation.

θ0 is the work of bond fracture across the interface and, for clean interfacial failure, is equal to the thermodynamic work of adhesion wA. Where failure is not purely interfacial, θ0 can be expressed as θ0=iI+r𝒯0+sF where i, r, and s are respectively the area fractions of interfacial, cohesive-in-rubber and cohesive-in-substrate failure, and I, θ0, and F are the intrinsic failure energies for the interface, rubber, and substrate, respectively.

It is believed that this work is the first to demonstrate explicitly and quantitatively the separate contributions of interfacial properties and bulk rheological behavior to the strength of adhesive joints.

1653. Neumann, A.W., R.J. Good, P. Ehrlich, P.K. Basu, and G.J. Johnston, “The temperature dependence of the surface tension of solutions of atactic polystyrene,” J. Macromolecular Science, B7, 525, (1973).

A technique is described for performing temperature scanning measurements of the surface tension of polymer solutions. Measurements on solutions of a high molecular weight and a low molecular weight monodisperse polystyrene in tetralin, decalin, and n-hexadecane are reported. Whereas previous investigations of other physical properties of polystyrene solutions had revealed only one anomaly, at about 50°C in some cases and at about 70–80°C in others, the curves presented here show two anomalies, near 45°C and 70°C, respectively. These anomalies are tentatively attributed to conformational changes of the polymer chains.

1652. Good, R.J., “The role of wetting and spreading in adhesion,” in Aspects of Adhesion, D.J. Alner and K.W. Allen, eds., 182-301, Transcripta Books, 1973.

689. Sessler, G.M., J.E. West, F.W. Ryan, and H. Schonhorn, “Increase of gold-teflon FEP joint strength by electron bombardment,” J. Applied Polymer Science, 17, 3199-3209, (1973).

The strength of joints between Teflon FEP (Type A) and 500- to 1000-Å gold layers deposited by evaporation can be greatly increased if the Teflon surface is subjected to electron-beam bombardment prior to the evaporation process. Typically, joint strengths of about 60 kg/cm2, approaching the bulk strength of Teflon, are obtained for treatments with electron-beam energies in the range of 5 to 20 keV and intercepted charge densities of about 5 X 10−6 C/cm2. This compares with gold–Teflon joint strengths of about 10 kg/cm2 for untreated material. The increase in joint strength is believed to be primarily due to crosslinking caused by the electron bombardment. Compared to the other known treatments to improve gold–Teflon joints, the present method has the advantage that the charge-storage properties of the Teflon are not irreversibly degraded. It is possible, for example, to store charge densities up to 3 X 10−8 C/cm2, on 25-μm films treated with this method, with the same favorable charge-retention properties and thermally stimulated current characteristics as obtained for untreated Teflon.

600. Wu, S., “Polar and nonpolar interactions in adhesion,” J. Adhesion, 5, 39-55, (1973).

Equations for polar and nonpolar interactions across the interface are developed by using energy additivity concept in a semi-continuum model. Interfacial and surface tensions of molten polymers are measured directly and used to test the resulting equations:

The first expression may be called the harmonic-mean equation preferred for low energy systems such as organic liquids, water, polymers, and organic pigments. The second may be called the geometric-harmonic-mean equation preferred for high energy systems such as mercury, glass, metal oxides and graphite. The third may be called the geometric mean equation which is found unsatisfactory. The harmonic-mean equation is used to obtain the “optimum” wettability condition for adhesion. The importance of polar interactions and matching of the polarity are analyzed and emphasized.

504. Kitzke, P.T., “Chemical and physical changes on polymer film surfaces due to electrical discharge treatment (PhD thesis),” Univ. of Colorado, 1973.

282. Panzer, J., “Components of solid surface free energy from wetting measurements,” J. Colloid and Interface Science, 44, 142-161, (1973).

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.

64. Collins, A.G.S., A.C. Lowe, and D. Nicholas, “An analysis of PTFE surfaces modified by exposure to glow discharges,” European Polymer J., 9, 1173-1185, (1973).

A detailed analysis is reported of the chemical and physical modifications which occur to PTFE surfaces exposed to glow discharges in ammonia gas and in air. The analytical methods used were infra-red attenuated total reflectance and differential attenuated total reflectance spectroscopy, X-ray photoelectron spectroscopy, contact angle measurements and scanning electron microscopy. The suitability for bonding with adhesives and the stability of the modified surfaces to attack by oxidizing acids are also reported.

1023. Ayres, R.L., and D.L. Shofner, “Preparing polyolefin surfaces for inks and adhesives,” SPE Journal, 28, 51-55, (Dec 1972).

1773. Bargeman, D., “Contact angles on nonpolar solids,” J. Colloid and Interface Science, 40, 344-348, (Sep 1972).

Contact angles of polar liquids on various nonpolar solids immersed in a nonpolar liquid have been measured. They agreed satisfactorily with values calculated by combining Young's equation either with measured contact angle data of the liquids on the substrates in air, or with the Fowkes relation valid at each of the interfaces. The latter method also applies when one of the liquids spreads on the substrate in air. Polyethene, polystyrene, polytetrafluorethene and glyceryltristearate were used as nonpolar solids; paraffin oil and heptane as nonpolar liquids; water and glycerol as polar liquids.

1798. Hamilton, W.C., “A technique for the characterization of hydrophilic solid surfaces,” J. Colloid and Interface Science, 40, 219-222, (Aug 1972).

The finding that the dispersion force contributions to the surface free energies of octane and water are equal enabled a simple method to be developed to characterize the hydrophilic nature of solid surfaces. This technique involves measuring octane contact angles on solid surfaces under water. Nonhydrophilic solids unable to interact by polar forces exhibit a predicted 50° contact angle, whereas those able to interact by polar forces give values greater than 50°. The greater the contact angle, the stronger are the polar interactions. The deviation of the contact angle from 50° can be used to evaluate, Isw, defined as the interfacial stabilization energy from the nondispersion (polar) forces.


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