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2865. Newman, S., “The effect of composition on the critical surface tension of polyvinyl butyral,” J. Colloid and Interface Science, 25, 341-345, (Nov 1967).

The critical surface tension γc of polyvinyl butyral has been measured with polyhydric alcohols and halogenated hydrocarbons. Despite variations in polymer composition (residual OH content) and modes of preparation, γc is found to be 24–25 dynes/cm. with the former class of liquids. The —CH3 groups appears to predominate over —CH2, ether oxygen, and OH groups present. Steric effect may account for this biasing of the γc values toward the lowest surface energy group present. Fowkes' relation based on dispersion force interactions only is found to fit the data reasonably well. Comparative data on polyethylene are also presented.

108. Fowkes, F.M., “Comments on 'The calculation of cohesive and adhesive energies', by J.F. Padday and N.D. Uffindell (letter),” J. Physical Chemistry, 72, 1407, (1968).

Sir: Padday and Uffindell produced a well organized and readable article, but unfortunately their mathematics is incorrect (by nearly one order of magnitude) because intermolecular potentials were integrated over molecular distances, breaking a fundamental principle of integral calculus.

215. Lee, L.-H., “Relationship between surface wettability and glass transition temperature of high polymers,” J. Applied Polymer Science, 12, 719-730, (1968).

The adhesion between a polymer and a solid substrate may be considered to be one type of complex liquid-solid interaction. Relationships between surface wettability and bulk properties of liquidlike polymers are discussed. A new and direct empirical relationship between the glass temperature (Tg) and critical surface tension of a polymer (γc) is established:

mathmatical formual
where n = degree of freedom, defined by Hayes, Vm = molar volume, and Φ = interaction parameter, or the ratio between reversible work of adhesion and geometrical mean of the work of cohesion. The effect of polarity and hydrogen bonding on this relationship is also discussed. The calculated γc's are much closer to the observed values than those calculated on the basis of parachor. With this new wettability relationship the wettability of polymers, especially of those forming no hydrogen bonds, can be related to thermal, rheological, mechanical, and relaxational properties.

280. Padday, J.F., and N.D. Uffindell, “The calculation of cohesive and adhesive energies from intermolecular forces at a surface,” J. Physical Chemistry, 72, 1407-1413, (1968).

Surface tensions of the n-alkanes and interfacial tensions between the n-alkanes and water have been calculated. The ca1culations use a modified form of the Moelwyn-Hughes' equation for the dispersion interaction between two particles, the integtation method of Hamaker to derive the total interaction across a plane surface, the geometric mean relationship of Good and Girifalco for the interaction of two dissimilar phases, and an assumption that the entropy of surface formation equals the difference between the interaction energy so calculated and the total intern&l energy of surface formation. The calculated surface tensions of the n-alkanes are compared with and agree well with experimentally determined values; also, some of their calculated interfacial-tension, contact-angle, and spreading-coefficient measurements with water all agree with the corresponding experimental values. For other systems, calculations are limited lo the contribution of the dispersion forces to the total interaction of the system.

281. Padday, J.F., and N.D. Uffindell, “Reply to comments of F.M. Fowkes on 'The calculation of cohesive and adhesive energies',” J. Physical Chemistry, 72, 3700-3701, (1968).

Surface tensions of the n-alkanes and interfacial tensions between the n-alkanes and water have been calculated. The ca1culations use a modified form of the Moelwyn-Hughes' equation for the dispersion interaction between two particles, the integtation method of Hamaker to derive the total interaction across a plane surface, the geometric mean relationship of Good and Girifalco for the interaction of two dissimilar phases, and an assumption that the entropy of surface formation equals the difference between the interaction energy so calculated and the total intern&l energy of surface formation. The calculated surface tensions of the n-alkanes are compared with and agree well with experimentally determined values; also, some of their calculated interfacial-tension, contact-angle, and spreading-coefficient measurements with water all agree with the corresponding experimental values. For other systems, calculations are limited lo the contribution of the dispersion forces to the total interaction of the system.

320. Schonhorn, H., and F.W. Ryan, “Effects of morphology in the surface region of polymers on adhesion and adhesive joint strength,” J. Polymer Science Part B: Polymer Physics, 6, 231-240, (1968).

The morphological character of the surface region of polyethylene has been considered with respect to adhesion and adhesive joint strength. By melting polyethylene onto a high-energy surface (e.g., aluminum) we have provided for extensive nucleation and the formation of a transcrystalline region in the polymer. Dissolution of the metal rather than peeling the metal from the polymer leaves the surface region of the polymer intact. The polymer sheet is now amenable to conventional adhesive bonding and forms a strong adhesive joint. We conclude from this study that the occurrence of the normal weak boundary layer is a consequence of the morphology of the surface region of the material and is, therefore, influenced by the method of preparation.

321. Schonhorn, H., “Heterogeneous nucleation of polymer melts on high-energy substrates, II. Effect of substrate on morphology and wettability,” Macromolecules, 1, 145-151, (1968).

Heterogeneous nucleation and crystallization of polymer melts against high-energy surfaces (eg, metals, metal oxides, and alkali halide crystals) have been found to result in markedchanges in both thesurface region morphology and wettability of these polymers even though the chemical constitution of the polymer is un-changed. The critical surface tensions (7c) of a variety of polymers nucleated against gold are considerably in excess of the commonly accepted values. Employing a modified Fowkes-Young equation can account for these sizable differences if the surface layer of these crystallizable polymers generated against high-energy surfaces is essentially crystalline.

322. Schonhorn, H., and R.H. Hansen, “Surface treatment of polymers, II. Effectiveness of fluorination as a surface treatment for polyethylene,” J. Applied Polymer Science, 12, 1231-1237, (1968).

An effective surface treatment for adhesive bonding of polyethylene has been developed. It involves exposing the polymer to an environment of elemental fluorine or fluorine diluted in argon. By this treatment, extensive fluorination of the surface region is effected. The fluorinated surface permits formation of strong adhesive joints by conventional adhesive bonding techniques even though the wettability of the new surface is similar to polytetrafluoroethylene. We believe that treatment of the polymer with elemental fluorine effectively eliminates the weak boundary layer associated with polyethylene by either crosslinking or by increasing the molecular weight in the surface region.

390. Wu, S., “Estimation of the critical surface tension for polymers from molecular constitution by a modified Hildebrand-Scott equation (notes),” J. Physical Chemistry, 72, 3332-3334, (1968).

The paper proposes a modified Hildebrand-Scott equation to estimate the critical surface tension of polymers based on their molecular constitution.

431. Burrell, H., “The challenge of the solubility parameter concept,” J. Paint Technology, 40, 197, (1968).

476. Hansen, R.H., “Interface conversion of polymers by excited gases,” in Symposium on Interface Conversion for Polymer Coatings, Elsevier, 1968.

1818. Pittman, A.G., D.L. Sharp, and B.A. Ludwig, “Polymers derived from fluoroketones II: Wetting properties of fluoroalkyl acrylates and methacrylates,” J. Polymer Science, Part A-1: Polymer Chemistry, 6, 1729-1740, (1968).

The critical surface tension of wetting (γc) for certain branched-chain polymeric fluoroalkyl acrylates and methacrylates was obtained. Polymeric materials utilized in this study can be represented by the repeating units

mathmatical formual
, where R is H or CH3, R′ is H or F, and X is F or Cl, by mathmatical formual, where n is 2, 5, or 11, and by mathmatical formual, where R is H or CH3 and n′ is 2 or 6. Monomer synthesis involved either the direct acylation of a fluoroketone–metal fluoride adduct or a fluoroalcohol with acryloyl or methacryloyl chloride or a displacement reaction between a fluoroketone–metal fluoride adduct and an ω-bromoester. In general, modifications in the pendent fluoroalkyl group affected γc in a manner predictable from previous work by Zisman et al.; e.g., γc was increased when either H or Cl was substituted for F in the side chain. In polymeric alkyl acrylates containing a heptafluoroisopropyl side chain γc increased as the fluorocarbon group was removed from the proximity of the polymer backbone by intervening methylene groups. A comparison of the wetting properties of polyacrylates containing either a perfluoroisopropyl or n-perfluoropropyl group showed that the polymer containing the isopropyl group had a lower γc.

2355. Bruno, M.F., “Method of flame treating and heat sealing a biaxially oriented heat shrinkable plastic film,” U.S. Patent 3361607, Jan 1968.

2318. Wood, H.H., “Method of improving the adhesive properties of polyolefin film by passing a diffuse electrical discharge over the film's surface,” U.S. Patent 3376208, Apr 1968.

1838. Roe, R.-J., “Surface tension of polymer liquids,” J. Physical Chemistry, 72, 2013-2017, (Jun 1968).

The interfacial tension along the boundary formed between two immiscible polymer liquids has been measured by the pendant drop method. The polymers employed for the study are polyethylene, polydimethylsiloxane, poly(ethylene oxide), polytetrahydrofuran, poly(vinyl acetate) and an ethylene-vinyl acetate copolymer. Surface tensions of these polymers (against air) were also determined by the same technique. The values of interfacial tension between polyethylene and each of the five polar polymers, together with the surface tension data, were utilized to calculate the separate contributions to the surface tension by dispersion and dipole interaction forces, in accordance with the procedure proposed by Fowkes. The interfacial tension between two polar polymers was then analyzed in terms of these separate components of forces. An empirical relation has been shown to correlate the dipole interaction term in interfacial tension with the individual dipole force components of the two polar polymers involved.

2356. Kaghan, W.S., P.M. Kay, and W.J. Schmitt, “Method for improving electric glow discharge treatment of plastic materials,” U.S. Patent 3391044, Jul 1968.

2357. Morgan, A.W., “Method of selectively treating a plastic film to improve anchorage characteristics,” U.S. Patent 3391070, Jul 1968.

2358. Hailstone, R.B., “Process of treating polyvinylbutyral sheeting by an electrical discharge in nitrogen to reduce blocking,” U.S. Patent 3407130, Oct 1968.

277. Owens, D.K., and R.C. Wendt, “Estimation of the surface free energy of polymers,” J. Applied Polymer Science, 13, 1741-1747, (1969).

A method for measuring the surface energy of solids and for resolving the surface energy into contributions from dispersion and dipole-hydrogen bonding forces has been developed. It is based on the measurement of contact angles with water and methylene iodide. Good agreement has been obtained with the more laborious γc method. Evidence for a finite value of liquid-solid interfacial tension at zero contact angle is presented. The method is especially applicable to the surface characterization of polymers.

323. Schonhorn, H., and F.W. Ryan, “Effect of polymer surface morphology on adhesion and adhesive joint strength, II. FEP Teflon and nylon 6,” J. Polymer Science Part B: Polymer Physics, 7, 105-111, (1969).

Heterogeneous nucleation and crystallization of FEP Teflon and nylon 6 melts against high energy surfaces (i.e., gold) produce an interfacial region, in these polymers, of high mechanical strength. Dissolution of the metal substrate rather than removal by mechanical means results in a polymer surface which is amenable to conventional structural adhesive bonding. Nucleation and crystallization of the polymer melts in contact with phases of low surface energy (e.g., vapor) result in the generation of weak boundary layers.

1288. Hall, J.R., C.A.L. Westerdahl, A.T. Devine, and M.J. Bodnar, “Activated gas plasma surface treatment of polymers for adhesive bonding,” J. Applied Polymer Science, 13, 2085-2096, (1969).

Polyethylene, polypropylene, poly(vinyl fluoride) (Tedlar), polystyrene, nylon 6, poly(ethylene terephthalate) (Mylar), polycarbonate, cellulose acetate butyrate, and a poly(oxymethylene) copolymer were treated with activated helium and with activated oxygen. Mechanical strengths of adhesive-bonded specimens prepared from treated and from untreated coupons were compared. Polyethylene (PE) and polypropylene (PP) showed the greatest increases in bond strength. Oxygen and helium were both effective with polyethylene, but polypropylene showed no improvement when treated with activated helium. The results with excited helium parallel the effects of ionizing radiation on these two polymers, as does the appearance of unsaturation bands in the infrared (965 cm−1 in PE, and 887 and 910 cm−1 in PP). Active nitrogen produced excellent bond strength with polyethylene but not with polypropylene. Of the remaining polymers examined, Tedlar, polystyrene, and nylon 6 showed the greatest improvement in bondability after treatment, and Mylar showed moderate improvement. Polycarbonate, cellulose acetate butyrate, and the poly(oxymethylene) copolymer gave approximately two-fold increases in lap-shear bond strength. In several cases, significant differences in response to time of treatment and type of excited gas were found.

1595. Padday, J.F., “Theory of surface tension,” in Surface and Colloid Science, Vol. 1, Matijevic, E., ed., John Wiley & Sons, 1969.

2219. Hall, J.R., C.A.L. Westerdahl, and M.J. Bodnar, “Activated gas plasma surface treatment of polymers for adhesive bonding,” in Picatinny Arsenal Technology Report 4001, 0, Picatinny Arsenal, 1969 (also in J. Applied Polymer Science, Vol. 13, p. 2085-2096, Oct 1969).

Polyethylene, polypropylene, poly(vinyl fluoride) (Tedlar), polystyrene, nylon 6, poly(ethylene terephthalate) (Mylar), polycarbonate, cellulose acetate butyrate, and a poly(oxymethylene) copolymer were treated with activated helium and with activated oxygen. Mechanical strengths of adhesive-bonded specimens prepared from treated and from untreated coupons were compared. Polyethylene (PE) and polypropylene (PP) showed the greatest increases in bond strength. Oxygen and helium were both effective with polyethylene, but polypropylene showed no improvement when treated with activated helium. The results with excited helium parallel the effects of ionizing radiation on these two polymers, as does the appearance of unsaturation bands in the infrared (965 cm−1 in PE, and 887 and 910 cm−1 in PP). Active nitrogen produced excellent bond strength with polyethylene but not with polypropylene. Of the remaining polymers examined, Tedlar, polystyrene, and nylon 6 showed the greatest improvement in bondability after treatment, and Mylar showed moderate improvement. Polycarbonate, cellulose acetate butyrate, and the poly(oxymethylene) copolymer gave approximately two-fold increases in lap-shear bond strength. In several cases, significant differences in response to time of treatment and type of excited gas were found.

2297. Johnson, R.E. Jr., and R.H. Dettre, “Wettability and contact angles,” in Surface and Colloid Science, Vol. 2, E. Matijevic, ed., 85-153, Wiley - Interscience, 1969.

2781. Grindstaff, T.H., “A simple apparatus and technique for contact angle measurements on small-denier single fibers,” Textile Research J., 39, 958+, (1969).

A simple apparatus and technique are described for measuring contact angles of liquids on small-denier fibers. This technique is based on the level-surface method and can be used to obtain either advancing or receding contact angles. Contact angles determined by this method are accurate and precise and the apparatus is inexpensive, rugged, easy to operate, and suitable for routine work.

2862. Mutchler, J., J. Menkart, and A.M. Schwartz, “Rapid estimation of the critical surface tension of fibers,” in Pesticidal Formulations Research (Advances in Chemistry Vol. 86, 7-14, American Chemical Society, 1969.

The theory of the flotation of a fiber-shaped solid by a liquid of lower density is presented in detail. Within the usual range of fiber diameters and densities, provided the cross section shows no protruding cusps, a very small positive contact angle is sufficient to float the fiber. If the contact angle is zero, the fiber will sink. The critical surface tension (CST) of a fiber surface can therefore be estimated by placing samples of the fiber on a series of liquids of progressively increasing surface tensions. The CST lies between the surface tensions of the liquid in which the fiber just sinks and the liquid in which it just floats. Agreement with the classical method is excellent.

1749. Crocker, G.J., “Elastomers and their adhesion,” Rubber Chemistry and Technology, 42, 30+, (Feb 1969).

2359. Leach, C.C., and R.L. Williams, “Apparatus for treating the surface of plastic bottles with an electrical spark discharge,” U.S. Patent 3428801, Feb 1969.

2360. Lough, J.C., “Reducing flame treatment of polyethylene terephthalate film prior to metalization,” U.S. Patent 3431135, Mar 1969.

1793. Dettre, R.H., and R.E. Johnson, Jr., “Surface tensions of perfluoroalkanes and polytetrafluoroethylene,” J. Colloid and Interface Science, 31, 568-569, (Apr 1969).

1515. Devine, A.T., and M.J. Bodnar, “Effects of various surface treatments on adhesive bonding of polyethylene,” Adhesives Age, 12, 35, (May 1969).

1772. Wu, S., “Surface and interfacial tensions of polymer melts I: Polyethylene, polyisobutylene, and polyvinyl acetate,” J. Colloid and Interface Science, 31, 153-161, (Oct 1969).

The surface tensions of polyethylene, polyisobutylene, and polyvinyl acetate, and the interfacial tensions of polyethylene/polyvinyl acetate and polyisobutylene/polyvinyl acetate systems have been measured by the pendent drop method in the temperature range up to 200°C. The results are analyzed in terms of the equations of Fowkes and of Girifalco and Good, and suggest that the conformational restriction of polymer molecules imparts a limitation on the extent of interfacial contacts and sharp phase boundaries in these systems. Several quantities of interest in adhesion, such as contact angle, spreading coefficient, and work of adhesion are also discussed.

1803. LeGrand, D.G., and G.L. Gaines, Jr., “The molecular weight dependence of polymer surface tension,” J. Colloid and Interface Science, 31, 162-167, (Oct 1969).

The surface tensions of a series of poly(isobutylenes) in the molecular weight range 400–3000 have been determined at 24°C. These results, together with surface tension values from the literature for poly(dimethyl siloxanes) and three series of different pure chain-molecule homologues, are found to exhibit a linear dependence on (molecular weight)−22. A simple free-volume argument seems to be consistent with this empirical observation.

1808. Petke, F.D., and B.R. Ray, “Temperature dependence of contact angles of liquids on polymeric solids,” J. Colloid and Interface Science, 31, 216-227, (Oct 1969).

Contact angles of water, glycerol, formamide, ethylene glycol, 1-bromonaphthalene, and bromobenzene were measured in the temperature range 5–160° on surfaces of polyethylene, polystyrene, polyacetal, polycarbonate, poly(ethylene terephthalate), and poly(tetrafluoroethylene-co-hexafluoropropylene). Stable advancing and receding angles were found and these varied linearly with temperature except in the range where solubility or swelling was evidence. Superheated water wet all the polymers to a greater degree than predicted. For the fluoropolymer all the liquids showed a negative temperature coefficient of the contact angle, both advancing and receding, ranging from 0.03 to 0.1 deg/°C. For the other polymers coefficients for advancing angles were nearly all negative and ranged from 0.03 to 0.18 but most receding angle values were positive; several liquid-polymer pairs showed a negligible coefficient. Temperature coefficients of the critical surface tension and of the dispersion surface tension of each solid were evaluated. Correlations of these derived quantities are discussed.

1817. Rastogi, A.K., and L.E. St. Pierre, “Interfacial phenomena in macromolecular systems III: The surface free-energies of polyethers,” J. Colloid and Interface Science, 31, 168-175, (Oct 1969).

The surface free-energies of the polyethers, polyethylene glycol, polypropylene glycol, polyepichlorohydrin, and polybutylene glycol, their mixtures and their random and block copolymers were determined by means of the pendant drop method. In all cases, except that of random copolymers, surface excesses of the low surface-energy component have been found. In the mixtures of homopolymers the behavior of surface excess isotherms depends on the molecular weight of the two components, while in block copolymers it depends on the degree of polymerization of the base unit. The Belton and Evans Equation for perfect solutions and the Prigogine equation for r-mer solutions have been applied to the experimental data.

1156. Pittman, A.G., and B.A. Ludwig, “Effect of polymer crystallinity on the wetting properties of certain fluoroalkyl acrylates,” J. Polymer Science Part A-1: Polymer Chemistry, 7, 3053-3066, (Nov 1969).

The wetting properties of a series of polyacrylates containing the fluoroalkyl group mathmatical formual have been studied. Where n is 7 and 9, the polyacrylates are highly crystalline at room temperature. Since the polymers were prepared under atactic free-radical conditions and the polyacrylates with shorter alkyl groups (where n is 3 or 5) were not crystalline at room temperature, the crystallinity is presumed to occur as a result of side-chain packing and not involve the backbone. The polymers become more wet-table (higher γc) as polymer crystallinity was reduced by quenching or heating past Tm. Correlations have been made between the work of Zisman and co-workers on the wetting properties of various fluorinated acid monolayers and the wetting properties of these fluoroalkyl acrylates. The results obtained in this study concerning the influence of polymer crystallinity on surface wetting are discussed in relation to the findings of Schonhorn and Ryan on the wettability of polyethylene single crystal aggregates.

53. Chan, R.K.S., “Surface tension of fluoropolymers, I. London dispersion term,” J. Colloid and Interface Science, 32, 492-498, (1970).

Surface tension is frequently expressed as the sum of a polar and a nonpolar term. In this paper an empirical approach is proposed for approximating the nonpolar term γsd of the surface tension of fluoropolymers. The experimental data were obtained from contact angle measurements employing a series of linear alkanes. These data are plotted by two different methods to evaluate γsd. The critical surface tension γe obtained from nonpolar contact angle liquids should reasonably approximate the γsd of the fluoropolymer surface. This work is based on classical molecular interactions, many concepts of which were established in earlier reports by Fowkes, Good, and Zisman.

54. Chan, R.K.S., “Surface tension of fluoropolymers, II. The polar attraction term,” J. Colloid and Interface Science, 32, 499-504, (1970).

It is generally accepted that the surface tension of fluoropolymers is approximately equal to the sum of a polar and nonpolar term. The first paper in this series described an empirical method for approximating the nonpolar term, and this paper proposes a similar approach for determination of the polar term, based upon contact angle measurements of polar liquids. The method is applicable to other solid surfaces provided suitable contact angle liquids are available.

69. Dann, J.R., “Forces involved in the adhesive process, I. Critical surface tensions of polymeric solids as determined with polar liquids,” J. Colloid and Interface Science, 32, 302-320, (1970).

Critical surface tensions γe of nine representative polymer surfaces with four series of polar liquids differed considerably from commonly accepted values. The Good-Girafalco-Fowkes-Young equation is used to explain the results, and it is shown that if certain precautions are observed, the equation may be used to predict γc of solid polymers for “standardized” series of liquids. The theoretical concepts of Fowkes and Good are shown to be compatible with Zisman's approach to the determination of γc. Serious errors may result, however, in the evaluation of contact angle data from misuse of the theoretical concepts of Fowkes or from misinterpretation of critical surface tension values as determined by the Zisman technique. Curve of cos θ vs. γL are straight lines only for one particular series of liquids and normal curves are of power form. It is suggested that many of the experimental contact angle data in the literature may be reinterpreted, including those for poly-(styrene), human skin, nylon 11, poly(ethylene), and monolayers of perfluorolauric acid.

70. Dann, J.R., “Forces involved in the adhesive process, II. Nondisperions forces at solid-liquid interfaces,” J. Colloid and Interface Science, 32, 321-331, (1970).

A modification of the Good-Girafalco-Fowkes-Young equation is used to calculate nondispersion interactions ISLP at the interface for nine polymeric solids and four polar series of liquids. The relationship of ISLP to work of adhesion WA and the spreading coefficient Se is shown. A linear relationship is found to exist between ISLP and γLP, the nondispersion energy component of the liquids, for the series of polar liquids and the solids studied. The slopes of the ISLP vs. γLP curves vary depending upon the polymer surface. Intercepts of the curves may be a measure of πs, the reduction in the surface energy of the solid resulting from adsorption of vapor from the liquid.

 

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