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1959. Kinloch, A.J., and G.K.A. Kodokian, “On the calculation of dispersion and polar force components of the surface free energy,” J. Adhesion, 34, 41-44, (Jun 1991).

Contact angle measurements have been widely used1–6 to calculate the values of the dispersion force, γ d s , and polar force, γ p s , components to the total surface free energy of a material using a derivation originally proposed by Kaelble.2 In this analysis a pair of simultaneous equations is derived which for two liquids, i and j, on a common solid surface may be written as:

where α is the contact angle of the liquid on the solid surface. Thus, if the values of α, γ d l , γ p l and γ l (where γ l = γ d l + γ p l ) for the two liquids are known, these equations may be solved to yield the dispersion, γ d d ;, and the polar, γ d s , force components to the surface free energy of the solid surface. The total surface free energy, γ s , is then simply the sum of these components.

1958. Bascom, W.D., and W.-J. Chen, “Effect of plasma treatment on the adhesion of carbon fibers to thermoplastic plastics,” J. Adhesion, 34, 99-119, (Jun 1991).

A study has been made of the effect of RF plasmas on the adhesion of carbon fibers to polycarbonate and polysulfone. Treatment in oxygen plasma significantly increased the adhesion to both polymers. The effect is lost if the treated fiber is stored in air for a week. Surface analysis using XPS indicated an increase in atom percent oxygen but the spectra were unchanged for the stored fibers even though there had been a significant loss in adhesion. It is suggested that oxygen surface functionality is responsible for the improved adhesion but that this surface activation is lost on storage. Due to a sampling depth of 5-10 nm, XPS would not be expected to detect this small change in surface functionality.

360. Sutherland, I., D.M. Brewis, R.J. Heath, and E. Sheng, “Modification of polypropylene surfaces by flame treatment,” Surface and Interface Analysis, 17, 507-510, (Jun 1991).

The changes induced on the surface of polypropylene homopolymer following flame treatment have been studied. Surface compositions were determined using x-ray photoelectron spectroscopy and compared to surface free energies estimated from contact angle measurements. The effect of air-to-gas ratio, total flow rate, contact time with the flame and the distance between the inner cone tip of the flame and the polymer have been investigated. Mild flame treatments were found to be effective in promoting the adhesion of polyurethane paints to the polypropylene. The adhesion between flame-treated polypropylene and the paint film was assessed using a composite butt test and the measured bond strengths were found to be well in excess of those obtained using solvent wiping or chlorinated polyolefin primers.

330. Sharma, M.K., “Surface phenomena in coatings and printing technology,” in Surface Phenomena and Fine Particles in Water-Based Coatings and Printing Technology, Sharma, M.K., and F.J. Micale, eds., 1-26, Plenum Press, Jun 1991.

This paper describes various aspects of water-based coatings and printing processes with special emphasis on the surface characteristics of coating/printing films. The film formation depends significantly on the surface properties of formulated coating/ink, and their interactions with substrates. Several surface parameters in relation to coating defects are briefly described. The mechanisms of printing processes and coating/ink film formation by water-based systems are presented. It has been shown that the formation of surface tension gradient during film curing determines the quality of the coating and printing films. Results demonstrate that the incorporation of suitable additives in the formulation can considerably minimize the crater formation. The hydrophilic-lipophilic balance (HLB) concept and the effect of surfactant concentration on pigment dispersion in an aqueous medium are discussed.

292. Podhajny, R.M., “Surface tension effects on the adhesion and drying of water-based inks and coatings,” in Surface Phenomena and Fine Particles in Water-Based Coatings and Printing Technology, Sharma, M.S., and F.J. Micale, eds., 41-58, Plenum Press, Jun 1991.

Water-based ink and coating use is reviewed with the emphasis on wetting and printing of film, metal, and metallized substrates. This paper addresses the effects of surface tension of water-based flexographic and rotogravure inks and coatings. The mode of drying in water-based technology is explored as well as static and dynamic surface tension of inks and coatings. Ink formulation and manufacturing considerations are reviewed to optimize surface tension effects for high speed presses. The role of substrate and ink transfer mediums are discussed relative to their impact on ink and coating drying rates. Corona treatment of film substrates is analyzed from the perspective of its effect on drying speed and ink adhesion. Suggestions are made to improve the quality performance of water-based ink and coatings through use of on-line surface tension equipment. Most importantly, the question “Why should I measure surface tension of my water-based ink?” is answered from the perspective of improving press productivity and ink performance.

202. Kumar, D., and S.N. Srisastava, “Wettability and surface energies of polymer substrates,” in Surface Phenomena and Fine Particles in Water-Based Coatings and Printing Technology, Sharma, M.S., and F.J. Micale, eds., 299-308, Plenum Press, Jun 1991.

The coating and printing of polymer films with water-based formulations are relatively difficult as compared to solvent-based formulations. The surface tension of water is higher than that of the solvents. In addition, the surface energy of polymer surfaces is in the range of 25–40 ergs/cm2. In order to understand the wetting and spreading behavior of coating materials, the polar and non-polar surface energies were evaluated by measuring contact angle of water and methylene iodide on various non-porous substrates. These results were utilized to explain the spreading, wettability and adhesion phenomena in order to understand the interactions between water-based coating/printing materials and non-porous substrates.

2218. Kaplan, S.L., and W.P. Hansen, “Plasma - the environmentally safe method to prepare plastics and composites for adhesive bonding and painting,” Presented at SAMPE Environmental Symposium, May 1991.

612. no author cited, “For rollers on high-power corona treaters: modifications defy harsh conditions,” Paper Film & Foil Converter, 65, 50, (May 1991).

1453. Kaplan, S.L., and P.W. Rose, “Plasma surface treatment of plastics to enhance adhesion,” Intl. J. Adhesion and Adhesives, 11, 109-113, (Apr 1991).

Adhesion, whether the bonding of polymers or the adhesion of coatings to polymer surfaces, is a recurring and difficult problem throughout the plastics industry. This paper introduces a proven, yet relatively unknown technology which provides an efficient, economic and versatile solution to adhesion problems: cold gas plasma surface treatment. Through plasma processing, it is possible to re-engineer the furface chemistry of any polymer to maximize its adhesive qualities. The result is optimum performance, even from inexpensive materials, and maximum flexibility in design decision-making.

417. Bataille, P., M. Dufourd, and S. Sapieha, “Graft polymerization of styrene onto cellulose by corona discharge,” Polymer Preprints, 32, 559-560, (Apr 1991).

332. Sharp, K.A., A. Nichols, R.F. Fine, and B. Honig, “Reconciling the magnitude of the microscopic and macroscopic hydrophobic effects,” Science, 252, 106-109, (Apr 1991).

The magnitude of the hydrophobic effect, as measured from the surface area dependence of the solubilities of hydrocarbons in water, is generally thought to be about 25 calories per mole per square angstrom (cal mol-1 Å-2). However, the surface tension at a hydrocarbon-water interface, which is a "macroscopic" measure of the hydrophobic effect, is ≈72 cal mol-1 Å-2. In an attempt to reconcile these values, alkane solubility data have been reevaluated to account for solute-solvent size differences, leading to a revised "microscopic" hydrophobic effect of 47 cal mol-1 Å-2. This value, when used in a simple geometric model for the curvature dependence of the hydrophobic effect, predicts a macroscopic alkane-water surface tension that is close to the macroscopic value.

1282. Chappell, P.J.C., J.R. Brown, G.A. George, and H.A. Willis, “Surface modification of extended chain polyethylene fibres to improve adhesion to epoxy and unsaturated polyester resins,” Surface and Interface Analysis, 17, 143-150, (Mar 1991).

Extended chain polyethylene fibres have been treated in ammonia and oxygen lo-pressure gas discharges (plasmas) in order to enhance adhesion to epoxy and unsaturated polyester resins, respectively, and thus significantly improve fibre/resin interfacial properties in fibre-reinforced polymer composites. Ammonia plasma treatment results in the incorporation of amine functional groups onto the fibre suface. The treated fibre surface has been analysed using XPS and spectrophotometric techniques. Extended chain polyethylene/epoxy composites made from ammonia, plasma-treated fibres show a marked increase in interlaminar shear strength over composites made from untreated, corona-treated or oxygen plasma-treated fibres. The increase in fibre/resin adhesion after ammonia plasma treatment is confirmed by SEM observations of fracture surfaces, which show clean interfacial fracture surfaces in composites made from treated fibres. Fibres modified by oxygen plasma treatment contain a significant concentration of carbon-oxygen functionalities, which contribute to the polarity of the surface and hence increase wet-out by unsaturated polyester resins. The concentration and nature of carbon-oxygen species on the fibre surface have been determined by XPS. Pull-out tests on multifilament yarns embedded in a polyester resin confirm the high fibre/matrix adhesion achieved with the oxygen plasma-treated fibres compared to corona-treated or untreated fibres. Tensile properties of the fibres are reduced significantly after prolonged treatment in an oxygen plasma, while in an ammonia plasma the fibre strength is unaffected.

614. no author cited, “Skip-treating technology fixes seal-failure problem,” Paper Film & Foil Converter, 65, 50, (Mar 1991).

613. no author cited, “Ceramic coat raises corona efficiency, lowers cost,” Converting World, 6, (Mar 1991).

456. Elwes, E.H., and C. Delahaye, “Adhesion problems associated with coating polypropylene,” Polymer Paint Colour Journal, 181, 151-152, (Mar 1991).

516. Lee, L.-H., “Recent studies in polymer adhesion mechanisms,” in Adhesive Bonding, Lee, L.-H., ed., 1-30, Plenum Press, Feb 1991.

In 1967, Lee published two papers on adhesion of high polymers(1,2) on the basis of the Buche—Cashin—Debye equation(3)

[ t e x ] D η = ( A ρ k T / 36 ) ( R 2 / M ) [ / t e x ]     ((1))

where D is the molecular diffusion constant, η the bulk viscosity, A Avogadro’s number, ρ the density, k Boltzmann’s constant, T the absolute temperature, M the molecular weight, and R 2 the mean-square end-to-end distance of a single polymer chain. It was concluded that the physical state of the polymer determines the major adhesion mechanism involved. Polymer adhesion can be subdivided into rubbery polymer-rubbery polymer adhesion (R—R adhesion), rubbery polymer—glassy polymer adhesion (R—G adhesion), and rubbery polymer—nonpolymer—solid adhesion (R—S adhesion). Diffusion, which depends to a great extent on the physical state of a polymer, is actually a limited selective process. Thus, diffusion of rubbery polymers can take place at the interface, but diffusion of a glassy polymer at a viscosity of 1013 poise or a diffusion constant of 10-21 cm2/sec appears to be nearly impossible. On the other hand, physical adsorption is common to all three types of the above adhesion systems.

515. Lee, L.-H., “Hard-soft acid-base (HSAB) principle for solid adhesion and surface interactions,” in Fundamentals of Adhesion, Lee, L.-H., ed., 349-362, Plenum Press, Feb 1991.

The donor—acceptor interaction(1,2) and the acid—base interaction(3) have been reviewed. On many occasions, the two terms, though different, have been used interchangeably to describe the interactions involving the exchange of electrons between a donor and an acceptor. For polymer adhesion, Fowkes(4,5) and Bolger et al. (6) have pointed out the important role of the acid-base interaction in the formation of an adhesive bond.

468. Gutowski, W.S., “Thermodynamics of adhesion,” in Fundamentals of Adhesion, Lee, L.-H, ed., 87-135, Plenum Press, Feb 1991.

217. Lee, L.-H., ed., Adhesive Bonding, Plenum Press, Feb 1991.

216. Lee, L.-H., ed., Fundamentals of Adhesion, Plenum Press, Feb 1991.

150. Haley, P.J., and M.J. Miksis, “The effect of the contact line on droplet spreading,” J. Fluid Mechanics, 223, 57-81, (Feb 1991).

143. Good, R.J., M.K. Chaudhury, and C.J. van Oss, “Theory of adhesive forces across interfaces, II. Interfacial hydrogen bonds as acid-base phenomena and as factors enhancing adhesion,” in Fundamentals of Adhesion, Lee, L.-H., ed., 153-172, Plenum Press, Feb 1991.

The theory of the apolar components of interfacial forces was examined in the previous chapter of this volume.(1) It has been possible to develop that theory of apolar components at this time owing to the existence of quantitative, mathematically formulated theories of forces between molecules (e.g., the London theory) together with the Lifshitz electromagnetic theory of the interaction of macroscopic bodies. (See the previous chapter for references.)

142. Good, R.J., and M.K. Chaudhury, “Theory of adhesive forces across interfaces, I. The Lifshitz-van der Waals component of interaction in adhesion,” in Fundamentals of Adhesion, Lee, L.-H., ed., 137-151, Plenum Press, Feb 1991.

The theory of the apolar components of interfacial forces was examined in the previous chapter of this volume.(1) It has been possible to develop that theory of apolar components at this time owing to the existence of quantitative, mathematically formulated theories of forces between molecules (e.g., the London theory) together with the Lifshitz electromagnetic theory of the interaction of macroscopic bodies. (See the previous chapter for references.)

96. Filbey, J.A., and J.P. Wightman, “Surface characterization in polymer/metal adhesion,” in Fundamentals of Adhesion, L.-H. Lee, ed., 175-202, Plenum Press, Feb 1991.

Adhesion involves a detailed understanding of polymer synthesis and characterization, mechanics, and surfaces. This chapter reviews surface analysis and interphase analysis emphasizing polymer/metal systems. The interphase is a thin region between the bulk adherend and the bulk adhesive, as depicted in Figure 1. A surface oxide, either native or one produced by pre-treatment, is present on most metal adherends. A primer is often applied in a production process after pretreatment and before the application of an adhesive. Typical thicknesses for the oxide are 0.003–0.4 µm, for the primer 4 µm (0.16 mil), and for the adhesive 40 µm (1.6 mil). The interphase region is expected to have mechanical properties different from either the adherend or the adhesive. Measurement of these properties is important in understanding adhesion, for example, poorly durable bonds are often a consequence of poor interphase properties.(1,2) Thus, one of the frontier areas in adhesion science today is determining interphase properties.

75. de Gennes, P.-G., “The dynamics of wetting,” in Fundamentals of Adhesion, Lee, L.-H., ed., 173-179, Plenum Press, Feb 1991.

72. Davis, G.D., “Characterization of surfaces,” in Fundamentals of Adhesion, Lee, L.-H., ed., 139-174, Plenum Press, Feb 1991.

63. Clearfield, H.M., D.K. McNamara, and G.D. Davis, “Adherend surface preparation for structural adhesive bonding,” in Fundamentals of Adhesion, Lee, L.-H., ed., 203-238, Plenum Press, Feb 1991.

This chapter summarizes our present understanding of surface preparations for structural adhesive bonding of aluminum, titanium, and steel adherends. Both the initial bond strength and the subsequent bond durability depend critically on the interaction of the adhesive (and/or primer) with a pretreated adherend. There are two mechanisms of adhesion that are prominent in structural adhesive bonding: mechanical interlocking of the polymer adhesive with a microscopically rough adherend surface, and chemical bonding (with either covalent bonds or weaker van der Waals bonds) of adhesive molecules to the (intentional) adherend oxide. The magnitude and relative importance of both of these interactions depend greatly on the nature of the adherend surface prior to bonding and on the rheology and chemistry of the adhesive.

422. Bezigian, T., “Why corona treating works,” Converting, 9, 12, (Jan 1991).

219. Leech, C.S. Jr., “Surface tension and surface energy: Practical procedures for printing on problem plastics,” ScreenPrinting, 81, 52-62, (Jan 1991).

2874. Sengupta, A., and H.P. Schreiber, “Surface characteristics of polyurethane adhesive formulations,” J. Adhesion Science and Technology, 5, 947-957, (1991).

The surface characteristics of a two-part polyurethane adhesive formulation, based on controlled amounts of polyol, isocyanate, and catalyst, have been studied by methods including contact angle analysis, 1R spectroscopy, and inverse gas chromatography (IGC). The response of surface properties to various cure regimes and to exposure to water has been established. IGC analyses show that the adhesive surface is mildly basic, and as first evaluated by contact angle methods, has a surface energy close to 40 mJ/m2. This is largely accounted for by dispersion forces. Following immersion in water at 60°C, however, the surface energies change, the most important effect being an increase in the non-dispersive component. FTIR spectra show that immersion in water also produces chemical changes in the surface region, likely related to enolization effects. On subsequent immersion of the adhesive surface in non-polar n-heptane, the non-dispersive component of the surface energy is again reduced, showing that surface restructuring of polyurethane chains contributes significantly to the observed surface dynamics. The magnitude of the restructuring effects was shown to vary with, but to persist for, all cure regimes applied to the formulation. The documented surface dynamics of the polymer are fully analogous to earlier results obtained for a series of two-part (soft-segment) polyurethanes. As expected, the surface dynamics in this family of polymers affect the bond strength of joints using the polyurethanes as adhesives.

2322. Goldshtein, D., “Modification of the surface of polytetrafluoroethylene in a glow discharge plasma in vapors of various organic compounds,” High Energy Chemistry, 25, 361-364, (1991).

The process of modifying the surface of polytetrafluoroethylene in a glow discharge plasma in vapors of organic compounds of various classes was investigated. It was established that the greatest increase of wettability is seen when modification is done in acrylic acid vapor. Multiple attenuated total internal reflection infrared spectroscopy was used to study the spectra of the coatings that formed and to demonstrate their difference in the case of acrylic acid.

2217. Masuda, S., S. Hosakawa, I. Tochizawa, K. Akutsu, K. Kuwano, and A. Iwata, “Surface treatment of plastic material by pulse corona induced plasma chemical process - PPCP,” in Proceedings of the IEEE Industry Applications Society Annual Meeting, Vol. 1, 703, IEEE, 1991.

A novel plasma chemical process PPCP (pulse corona induced plasma chemical process) can produce copious active radicals in air under NTP (normal temperature and pressure) by using an extremely fast rising narrow high voltage pulse between corona electrodes and grounded counter electrodes so that intense streamer coronas are generated. This provides an effective means of surface treatment to a plastic material placed between the two electrodes through generation of free bonds on the surface directed to the corona electrodes. Special features of this method are that it can cope with a complex shape of the material to be treated, and that it does not spark even at the periphery near the grounded counter electrode. This method is suitable for the surface treatment of polypropylene bumpers so as to provide a strong adhesion of color paint to it. The adhesion strength of a paint film is raised from zero to ca. 1000 g/cm/sup 2/ by PPCP treatment for 60 seconds.

1912. Webster, H.F., and J.P. Wightman, “Effects of oxygen and ammonia plasma treatment on polypropylene sulfide thin films and their interaction with epoxy adhesive,” J. Adhesion Science and Technology, 5, 93-106, (1991) (also in Acid-Base Interactions: Relevance to Adhesion Science and Technology, K.L. Mittal and H.R. Anderson Jr., eds., p. 329-342, VSP, Nov 1991).

X-Ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS) were used to study the chemical modification of polyphenylene sulfide (PPS) thin films on exposure to both oxygen and ammonia plasmas. The XPS results for the oxygen plasma treatment indicated a large oxygen increase with the incorporation of various oxidized carbon species as well as oxidized sulfur. For the ammonia plasma, both nitrogen and oxygen were incorporated. IRRAS proved to complement the XPS results, showing a wide range of CSingle Bond O and CDouble BondO functionalities incorporated on oxygen plasma exposure. For the ammonia plasma treatment, an increase in hydrocarbon, alkene-type fragments, and possibly amine groups was detected. Both the XPS and IRRAS results indicated that exposure of plasma-treated surfaces to epoxy with subsequent carbon tetrachloride washes removed most of the modification originally present after plasma treatment. IRRAS analysis showed that a thin layer of epoxy remained after repeated solvent washes and that the film seemed to be cured. For untreated PPS films, a non-cured epoxy film adsorbed. This work suggests that the plasma-modified layer plays a role in the formation of a covalent interphase region between PPS and epoxy.

1911. Whitesides, G.M., H.A. Biebuyck, J.P. Folkers, and K.L. Prime, “Acid-base interactions in wetting,” J. Adhesion Science and Technology, 5, 57-69, (1991) (also in Acid-Base Interactions: Relevance to Adhesion Science and Technology, K.L. Mittal and H.R. Anderson Jr., eds., p. 229-242, VSP, Nov 1991).

The study of the ionization of carboxylic acid groups at the interface between organic solids and water demonstrates broad similarities to the ionizations of these groups in homogeneous aqueous solution, but with important systematic differences. Creation of a charged group from a neutral one by protonation or deprotonation (whether -NH3+ from -NH2 or -CO2- from -CO2H) at the interface between surface-functionalized polyethylene and water is more difficult than that in homogeneous aqueous solution. This difference is probably related to the low effective dielectric constant of the interface (ε≃9) relative to water (ε≃80). It is not known to what extent this difference in ε (and in other properties of the interphase, considered as a thin solvent phase) is reflected in the stability of the organic ions relative to their neutral forms in the interphase and in solution, and to what extent in differences in the concentration of H+ and OH- in the interphase and in solution. Self-assembled monolayers (SAMs)-especially of terminally functionalized alkanethiols (HS(CH2)nX) adsorbed on gold-provide model systems with relatively well-ordered structures that are useful in establishing the fundamentals of ionization of protic acids and bases at the interface between organic solids and water. These systems, coupled with new analytical methods such as photoacoustic calorimetry (PAC) and contact angle titration, may make it possible to disentangle some of the complex puzzles presented by proton-transfer reactions in the environment of the organic solid-water interphase.

1797. Hsieh, Y.-L., S. Xu, and M. Hartzell, “Effects of acid oxidation on wetting and adhesion properties of ultra-high modulus and molecular weight polyethylene (UHMWPE) fibers,” J. Adhesion Science and Technology, 5, 1023-1039, (1991).

The effects of acid oxidation on the surface properties of gel-spun ultra-high modulus and molecular weight polyethylene (UHMWPE) fibers were investigated. Three acid-assisted reactions with CrO3 (I), K2Cr2O, (II), and one base-catalyzed reaction with K2Cr2O7 (III) were studied. In reaction II, two levels of sulfuric acid were used for IIa and IIb, with reaction IIa containing the higher concentration. Under the reaction conditions chosen, i.e. 1 min at 23°C, the effects of these oxidations were restricted to the fiber surfaces. All oxidation reactions either significantly reduced or eliminated the axially oriented macrofibril striations and changed the lamellae perpendicular to the fiber axis to irregular hairline surface structures. The oxidative attacks on the fiber surfaces appeared to have occurred in the fibrillar structure and likely at the disorder regions along the fibrils. The epoxy resin wettability and the interfacial adhesion to the epoxy resin were both improved with reactions I and IIa, whereas reaction III did not affect either of these properties. A positive relationship between surface wettability and interfacial adhesion on single fibers was observed on the untreated and acid oxidized gel-spun UHMWPE fibers.

1688. Kanda, N., M. Kogoma, H. Jinno, H. Ychiyama, and S. Okazaki, “Atmospheric pressure glow plasma discharge and its application to surface treatment and film deposition,” in Proceedings of the 10th International Symposium on Plasma Chemistry, Vol. 3, 3.2.201-204, ISPC, 1991.

1583. Friedrich, J., I. Loeschcke, H. Frommelt, et al, “Aging and degradation of poly(ethylene-terephthalate) in an oxygen plasma,” Polymer Degradation and Stability, 31, 97-114, (1991).

The ageing of thin PET films in an oxygen plasma was investigated. After several hours exposure a large decrease in mechanical strength was observed. Plasma particle bombardment, chemical reactions and the plasma vacuum UV radiation cause extensive chemical and structural changes. The chemical reactions leading to the ageing process were identified.

1552. no author cited, “Technical bulletin: A recommended practice for evaluating surface treatment of polyethylene and polypropylene containers,” Society of the Plastics Industry, 1991.

1454. Youxian, D., H.J. Griesser, A.W.H. Mau, R. Schmidt, and J. Liesegang, “Surface modification of polytetrafluoroethylene by gas plasma treatment (to increase the surface energy),” Polymer, 32, 1126-1130, (1991).

Poly(tetrafluoroethylene) (PTFE) samples were surface modified in gas plasma atmospheres of air, oxygen, argon and water vapour in order to increase the surface energy. Its dispersive and polar components were determined by contact angle measurements after various treatment times. Plasma treatment times of only 15s were sufficient in all gases studied for substantial surface modification of PTFE. The chemical composition of the surfaces was studied by X-ray photoelectron spectroscopy (X.p.s.). The main results of all the plasma treatments were the abstraction of fluorine and the production of surface crosslinks, whereas only a low level of oxygen-containing groups was attached into the surface layer.

1329. Moy, E., P. Cheng, Z. Policova, S. Treppo, D. Kwok, D.R. Mack, et al, “Measurement of contact angles from the maximum diameter of non wetting drops by means of a modified axisymmetric drop shape analysis,” Colloids and Surfaces, 58, 215-227, (1991).

A modified axisymmetric drop shape analysis approach, ADSA-MD (maximum diameter) was developed to measure the contact angles of non-wetting drops front top-view images of the drop. The approach numerically solves the Laplace equation of capillarity given the following input parameters: maximum diameter and volume of the drop, liquid surface tension, density difference between the two fluid phases and the gravity constant. The computed contact angles are in good agreement with those from ADSA-P, an approach which uses the profile of the drop to determine the contact angle. This new technique is particularly suited for systems where the quality of the solid substrate is poor, such as in the case of biological systems. For these situations contact angle determination from the profile is difficult, if not impossible, due to the difficulty in locating the three-phase contact line. The ADSA-MD approach was used to determine the contact angle of water sessile drops on colon sections of New zealand white rabbits.


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