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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.

1298. Li, D., and A.W. Neumann, “Thermodynamics of contact angle phenomena in the presence of a thin liquid film,” Advances in Colloid and Interface Science, 36, 125-151, (1991).

The effects of a thin liquid film on contact angles are studied using a simplified thermodynamic model. (in this model, the small transition zone between the liquid-vapour interface and the fiat thin liquid film is neglected). A set of mechanical equilibrium conditions have been derived for contact angle systems with a flat thin liquid film. The equilibrium condition at the three-phase intersection explicitly predicts the effects of the film tension, the disjoining pressure and the film thickness, on contact angles.

The number of degrees of freedom for a two-component solid-liquid-vapour surface system with a flat thin liquid film is shown to be three, implying the existence of an equation-of-state-type relationship among the solid-liquid interfacial tension, γsl, liquid surface tension, γlv, the disjoining pressure, Π, and the film tension, γf. An approximate, explicit form of such an equation of state has been derived. The combination of this equation of state with the equilibrium condition of the the three-phase intersection can be used to estimate the film tension, γf, and the solid-liquid interfacial tension, γsl, from the measured data for the vapour pressure, Pv, the film thickness, h, the curvature of the liquid-vapour meniscus, J, the liquid surface tension, γlv, and the contact angle, θ.

The effect of the thin film on the drop-size dependence of contact angles is also investigated and found to be negligible.

1297. Budziak, C.J., E.I. Vargha Butler, and A.W. Neumann, “Temperature dependence of contact angles on elastomers,” J. Applied Polymer Science, 42, 1959-1964, (1991).

Contact angle measurements with three different liquids were performed on: (i) butyl rubber PB 101-3 (Polysar Ltd.) and (ii) Dow Corning 236 dispersion. Contact angles were measured at different temperatures within the range from 23°C (room temperature) to 120°C. The surface tensions, γsv, of the polymeric coatings at each temperature were calculated from the contact angles. The temperature coefficients of the surface tensions, dγsv/dT, i.e., the surface entropies, were established for the temperature range covered.

1290. Kinloch, A.J., G.K.A. Kodokian, and J.F. Watts, “Relationships between the surface free energies and surface chemical compositions of thermoplastic fibre composites and adhesive joint strengths,” J. Materials Science Letters, 10, 815-818, (1991).

1153. Harrington, W.F. Jr., “Surface treatment of plastics,” in Coatings Technology Handbook, D. Satas, ed., Marcel Dekker, 1991 (also in Coatings Technology Handbook, 2nd Ed., D. Satas and A.A. Tracton, eds., p. 335-342, Marcel Dekker, Jan 2001, and Coatings Technology: Fundamentals, Testing, and Processing Techniques, A.A. Tracton, ed., p. 38/1-38/7, CRC Press, Oct 2006).

No single step in the coating process has more impact on film adhesion than surface preparation. Film adhesion to a plastic is primarily a surface phenomenon and requires intimate contact between the substrate surface and the coating. However, intimate contact of that plastic surface is not possible without appropriate conditioning and cleansing. Plastic surfaces present a number of unique problems for the coater. Many plastics, such as polyethylene or the fluorinated polymers, have a low surface energy. Low surface energy often means that few materials will readily adhere to the surface. Plastic materials often are blends of one or more polymer types or have various quantities of inorganic fillers added to achieve specific properties. The coefficient of thermal expansion is usually quite high for plastic compounds, but it can vary widely depending on polymer blend, filler content, and filler type. Finally, the flexibility of plastic materials puts more stress on the coating, and significant problems can develop if film adhesion is low due to poor surface preparation.

993. Corn, S., K.P. Vora, M. Strobel, and C.S. Lyons, “Enhancement of adhesion to polypropylene films by chlorotrifluoromethane plasma treatment,” J. Adhesion Science and Technology, 5, 239-245, (1991).

The surface chemical modification of polypropylene by CF3Cl plasma treatment was studied by ESCA, wettability measurements, and pressure-sensitive-adhesive performance tests. Improved adhesion was observed on polypropylene treated under CF3Cl plasma conditions that maximized Cl and minimized F and O incorporation. Polypropylene treated using CF3Cl plasmas had a high dispersive component of surface energy, as indicated by low diiodomethane contact angles. High dispersive energy is characteristic of chlorinated surfaces, and may contribute to the improved adhesion.

912. Fogarty, W., “Wetting tension test kits,” Select Industrial Systems, 1991.

876. Dahlquist, C.A., “The theory of adhesion,” in Coatings Technology Handbook, Satas, D., ed., 51-61, Marcel Dekker, 1991 (also in Coatings Technology Handbook, 2nd Ed., D. Satas and A.A. Tracton, eds., p. 51-61, Marcel Dekker, Jan 2001, and Coatings Technology: Fundamentals, Testing, and Processing Techniques, A.A. Tracton, ed., p. 5/1-5/9, CRC Press, Oct 2006).

875. Gilleo, K.B., “Rheology and surface chemistry,” in Coatings Technology Handbook, Satas, D., ed., 3-19, Marcel Dekker, 1991 (also in Coatings Technology Handbook, 2nd Ed., D. Satas and A.A. Tracton, eds., p. 3-17, Marcel Dekker, Jan 2001, and Coatings Technology: Fundamentals, Testing, and Processing Techniques, A.A. Tracton, ed., p. 1/1-1/9, CRC Press, Oct 2006).

A basic understanding of rheology and surface chemistry, two primary sciences of liquid flow and solid-liquid interaction is necessary for understanding coating and printing processes and materials. A generally qualitative treatment of these subjects will suffice to provide the insight needed to use and apply coatings and inks and to help solve the problems associated with their use. Rheology, in the broadest sense, is the study of the physical behavior of all materials when placed under stress. Four general categories are recognized: elasticity, plasticity, rigidity, and viscosity. Our concern here is with liquids and pastes. The scope of rheology of fluids encompasses the changes in the shape of a liquid as physical force is applied and removed. Viscosity is a key rheological property of coatings and inks. Viscosity is simply the resistance of the ink to flow-the ratio of shear stress to shear rate. Throughout coating and printing processes, mechanical forces of various types and quantities are exerted. The amount of shear force directly affects the viscosity value for non-Newtonian fluids. Most coatings undergo some degree of" shear thinning" phenomenon when worked by mixing or running on a coater. Heavy inks are especially prone to shear thinning. As shear rate is increased, the viscosity drops, in some cases, dramatically. This seems simple enough except for two other effects. One is called the yield point. This is the shear rate required to cause flow. Ketchup often refuses to flow until a little extra shear force is applied. Then it often flows too freely. Once the yield point has been exceeded the solidlike behavior vanishes. The loose network structure is broken up. Inks also display this yield point property, but to a lesser degree. Yield point is one of the most important ink properties.

842. Borch, J., “Thermodynamics of polymer-paper adhesion: A review,” J. Adhesion Science and Technology, 5, 523-541, (1991).

A review of studies of polymer-paper adhesion illustrates the thermodynamic nature of the bondability of polymers to plain, uncoated paper surfaces. The bond strength depends strongly on the chemical nature of the polymer surface and on that of the fibrous paper surface. Adhesion to paper may be characterized indirectly through thermodynamic analysis of the paper substrate, or directly through paper laminate or adhesion tape peel testing. The need for adequate paper adhesion is emphasized, particularly for some of the newer printing processes (electrophotographic and thermal imaging). It is concluded that some of the indirect methods of adhesion characterization (surface energetics analysis via contact angle measurements or the inverse gas chromatography technique) may serve to characterize paper adhesion in these processes.

761. Milker, R., and A. Koch, “Surface treatment of polymer webs by fluorine,” in Coatings Technology Handbook, Satas, D., ed., 303-309, Marcel Dekker, 1991 (also in Coatings Technology Handbook, 2nd Ed., D. Satas and A.A. Tracton, eds., p. 359-365, Marcel Dekker, Jan 2001, and Coatings Technology: Fundamentals, Testing, and Processing Techniques, A.A. Tracton, ed., p. 41/1-41/6, CRC Press, Oct 2006).

760. Kaplan, S.L., and P.W. Rose, “Plasma surface treatment,” in Coatings Technology Handbook, Satas, D., ed., 295-301, Marcel Dekker, 1991 (also in Coatings Technology Handbook, 2nd Ed., D. Satas and A.A. Tracton, eds., p. 351-357, Marcel Dekker, Jan 2001, and Coatings Technology: Fundamentals, Testing, and Processing Techniques, A.A. Tracton, ed., p. 40/1-40/6, CRC Press, Oct 2006).

759. Lindland, H.T., “Flame surface treatment,” in Coatings Technology Handbook, Satas, D., ed., 287-294, Marcel Dekker, 1991 (also in Coatings Technology Handbook, 2nd Ed., D. Satas and A.A. Tracton, eds., p. 343-350, Marcel Dekker, Jan 2001, and Coatings Technology: Fundamentals, Testing, and Processing Techniques, A.A. Tracton, ed., p. 39/1-39/7, CRC Press, Oct 2006).

692. Mount, E.M. III, and A.J. Benedict, “Metallisable heat-sealable, oriented polypropylene film has layer of copolyester to improve bonding to metal,” European Patent #444340, 1991.

656. Vargo, T.G., and J.A. Gardella Jr., “Modification of surfaces designed for cell growth studies,” in Polymer - Solid Interfaces, Pireaux, J.J., P. Bertrand, and J.L. Bredas, eds., 485-494, Institute of Physics Publishing, 1991.

652. Silvain, J.F., A. Veyrat, and J.J. Ehrhardt, “Morphology and adhesion of magnesium thin films evaporated on polyethylene terephthalate,” in Polymer - Solid Interfaces, Pireaux, J.J., P. Bertrand, and J.L. Bredas, eds., 281-287, Institute of Physics Publishing, 1991.

649. Nowak, S.M., M. Collaud, et al, “Polymer - metal interface formation after in-situ plasma and ion treatment,” in Polymer - Solid Interfaces, Pireaux, J.J., P. Bertrand, and J.L. Bredas, eds., 257-280, Institute of Physics Publishing, 1991.

648. Morra, M., E. Occhiello, and F. Garbassi, “Dynamics of plasma treated polymer surfaces: mechanisms and effects,” in Polymer - Solid Interfaces, Pireaux, J.J., P. Bertrand, and J.L. Bredas, eds., 407-428, Institute of Physics Publishing, 1991.

645. Liston, E.M., “Plasma modification of polymer surfaces,” in Polymer - Solid Interfaces, Pireaux, J.J., P. Bertrand, and J.L. Bredas, eds., 429-454, Institute of Physics Publishing, 1991.

629. David, D.J., “Fundamental concepts in the interfacial adhesion of laminated safety glass,” in Polymer - Solid Interfaces, Pireaux, J.J., P. Bertrand, and J.L. Bredas, eds., 133-144, Institute of Physics Publishing, 1991.

626. Chakraborty, A.K., “Progress and future directions in the theory of strongly interacting polymer - solid interfaces,” in Polymer - Solid Interfaces, Pireaux, J.J., P. Bertrand, and J.L. Bredas, eds., 3-35, Institute of Physics Publishing, 1991.

592. Waddington, S., and D. Briggs, “Adhesion mechanisms between polymer coatings and polypropylene studied by X-ray photoelectron spectroscopy and secondary ion mass spectrometry,” Polymer Communications, 32, 506-508, (1991).

580. Strobel, J.M., M. Strobel, C.S. Lyons, C. Dunatov, and S.J. Perron, “Aging of air-corona-treated polypropylene film,” J. Adhesion Science and Technology, 5, 119-130, (1991).

X-ray photoelectron spectroscopy (ESCA), wettability measurements, and an ink adhesion test were used to characterize changes in the surface properties of air-corona-treated polypropylene (PP) films upon aging under a variety of storage conditions. No changes in ESCA O/C atomic ratios as a function of aging were observed for corona-treated PP films. The wettability data indicated a slight decrease in wettability upon aging. Aging did not affect ink adhesion for the particular PP and ink studied. The responses obtained were independent of the various film storage conditions employed. The slight decrease in wettability observed upon aging was attributed to reorientation of oxidized functionalities within the surface region.

576. Shu, L.-K., “Contact angles and determination of the components of surface energy of polymer surfaces (PhD dissertation),” SUNY Buffalo, 1991.

572. Sherman, P.B., “Additive influence in corona treatment,” in 1991 Film Extrusion Short Course, 119-130, TAPPI Press, 1991.

567. Sengupta, K.S., and H.K. Birnbaum, “Structural and chemical effects of low-energy ion bombardment of PMMA-ODA surfaces,” J. Vacuum Science and Technology, A9, 2928-2935, (1991).

The effects of ion irradiation on polyimide surfaces have been studied using x‐ray photoemission techniques. Ion bombardment with energies in the range 0.5–2.0 keV and doses between 8×1013 and 1×1015 ions/cm2 were carried out in situ in the x‐ray photoelectron spectrometer and the chemistry of the modified surface was monitored using core level spectral changes. At low doses and energies, carbonyl groups were preferentially sputtered keeping the rest of the monomer intact. Loss of nitrogen was insignificant compared to losses of carbon and oxygen. At higher energies and doses, the polymer undergoes extensive bond scission, restructuring of various functional groups and species, together with radical and anion formation. High resolution spectra indicated a binding energy scale shift to a lower value, which increased with ion energy and dose, and which was related to the creation of a surface negative charge. The effects of exposure to moisture in the ambient on the surface charge, on the surface structure, and on the surface chemistry was studied.

557. Savolainen, A., J. Kuusipalo, and H. Karhuketo, “Optimization of corona and flame pretreatment in multilayer coating,” in 1991 Extrusion Coating Short Course (Dusselfdorf), 333-340, TAPPI Press, 1991.

544. Pireaux, J.J., P. Bertrand, and J.L. Bredas, eds., Polymer - Solid Interfaces, Institute of Physics, 1991.

520. Liu, D., “Surface modification of polystyrene by plasma treatment (MS thesis),” Univ. of Massachusetts, 1991.

489. Ishiguro, S., “Surface tension of aqueous polymer solutions (MS thesis),” Univ. of Illinois, Chicago, 1991.

432. Cai, G., M.H. Litt, and I.M. Krieger, “Surface properties and abhesion of undecyl oxazoline block and homopolymers,” J. Polymer Science Part B: Polymer Physics, 29, 773-784, (1991).

The surface properties of three undecyl oxazoline homopolymers and two phenyl/undecyl oxazoline block copolymers (as comparison) were studied. After coating on glass slides and annealing, all films had a low critical surface energy of 21 dynes/cm. Water contact angles were higher than 107° for the most hydrophobic films. The deduction that the polymer surfaces contained close-packed methyl groups was further confirmed by electron spectroscopy chemical analysis (ESCA) angle profiling on an annealed undecyl oxazoline homopolymer film. A model was developed for the variation of elemental ratios as a function of photoelectron take-off angle. This verified that the polymer films had the polymer backbones parallel to the surface with the undecyl tails oriented toward the surface. When these block and homopolymers were coated on copy paper and glass slides, the peel strengths of pressure-sensitive adhesives with these surfaces were very low for short dwell times at room temperature. At long dwell times or at elevated temperatures, the peel strengths remained low for the homopolymers but increased greatly for the block copolymers to values higher than those in the tape on glass. After 24 h at 70°C, ESCA analysis showed that the adhesive diffused into the phenyl block domains of the diblock copolymer, generating high peel strength and cohesive failure. However, under the same annealing conditions, the triblock copolymer showed adhesive failure while peel strength increased. ESCA analysis showed very litle diffusion of the adhesive into the triblock copolymer. The homopolymers were stable toward vinyl acetate type adhesives even at elevated temperature; they were abhesive up to 100°C with no interdiffusion.

374. Vargo, T.G., D.J. Hook, J.A. Gardella Jr., M.A. Eberhardt, A.E. Meyer, and R. Baier, “A multitechnique surface analytical study of a segmented block copolymer poly(ether-urethane) modified through an H2O radio frequency glow discharge,” J. Polymer Science Part A: Polymer Chemistry, 29, 535, (1991).

Recent work in our laboratories has fully characterized the surface region of a segmented poly(ether-urethane) (PEU) extending from the air/polymer interfacial region through bulk depths in the micron range. This characterization utilized energy and angle dependent Electron Spectroscopy for Chemical Analysis (ESCA), Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR–FTIR), and Comprehensive Wettability Profiling (contact angle using a homologous series of liquids) as defined by Zisman. In this study this same multi-analytical-technique approach is used to elucidate changes in these PEU surfaces induced through an H2O Radio Frequency Glow Discharge (RFGD) plasma. This investigation reports both qualitative and quantitative changes due to the modification treatments as well as the permanency of the changes effected on these surfaces through the plasma treatment. From our analyses, the amount of surface residing polyurethane (hard segment) is observed to increase due to a proposed plasma etching mechanism. Further, the addition of oxygen containing functionality is detected at the modified surfaces unique with respect to the unmodified PEU. These surface modifications which show large increases in wettability, are finally observed to be semi-permanent over a time period of 6 months.

370. Uyama, Y., H. Inoue, K. Ito, A. Kishida, and Y. Ikada, “Comparison of different methods for contact angle measurement,” J. Colloid and Interface Science, 141, 275-279, (1991).

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.

309. Sanchez-Rubio, M., J.R. Castellanos-Ortega, and J.E. Puig, “An analytical balance as tensiometer and densimeter,” J. Chemical Education, 68, 158-160, (1991).

How to convert an analytical balance into an accurate ring tensiometer or densimeter.

307. Sakata, I., M. Morita, H. Furuichi, and Y. Kawaguchi, “Improvement of plybond strength of paperboard by corona treatment,” J. Applied Polymer Science, 42, 2099-2104, (1991).

It was found that the treatment of the surfaces of wet pulp sheets (moisture content; up to 85%) in a corona discharge improved greatly the plybond strength of the paperboard obtained when the treated wet pulp sheets were laminated together, pressed, and then dried. Treatment was carried out by use of a corona apparatus which had variable driven roll electrodes for transporting the wet pulp sheets through a corona field and was attached to a high-voltage generator (∼ max 500 W, ∼ 16 kV at 5 kHz). The plybond strengths of the paperboards were examined by means of Tappi RC-273 and JIS P8139 methods. Some experiments regarding the chemical effects of the corona treatment on the surface modification of wet pulp sheets were made with the aid of dye adsorption methods. Both untreated and corona-treated pulps adsorbed basic dyes, methylene blue, etc., with the same extent of dyeing. This indicates that no measurable acidic sites (carboxyl groups) increased on the surfaces of the pulp sheets during the corona treatment. To detect aldehyde groups, the dyeing examination of the pulps with Schiff's reagent was made, and the results showed a higher dyeing ability for the corona-treated pulps compared to the untreated, indicating that aldehyde groups on the pulp surfaces increased with an increase in the degree of corona treatment. The corona treatment seems to produce on the surface layer lightly oxidized and fairly degraded polysaccharide chains, which will tend to swell in water and thus act as an adhesive in plybonding the pulp sheets.

271. Onyiriuka, E.C., L.S. Hersh, and W. Hertl, “Solubilization of corona discharge- and plasma-treated polystyrene,” J. Colloid and Interface Science, 144, 98-102, (1991).

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 CSingle BondC 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.

265. Occhiello, E., M. Morra, F. Garbassi, D. Johnson, and P. Humphrey, “SSIMS studies of hydrophobic recovery: oxygen plasma treated PS,” Applied Surface Science, 47, 235-242, (1991).

SSIMS (static secondary ion mass spectroscopy) has been used to aid in the interpretation of hydrophobic recovery of oxygen plasma treated PS (polystyrene), together with XPS (X-ray photoelectron spectroscopy) and water contact angle measurements.

The heterogeneity in sputter yields of different ions did not allow complete qualitative and quantititative information to be obtained. Yet negative ion spectra of surfaces treated with plasmas of isotopically enriched oxygen allowed us to follow closely the disappearance of polar groups during hydrophobic recovery. Furthermore, using isotopically enriched PS samples, it was possible to obtain unambiguous information about molecular weight and temperature-induced changes in the hydrophobic recovery mechanism, which could not have been provided by XPS.

264. Occhiello, E., M. Morra, G. Morini, F. Garbassi, and P. Humphrey, “Oxygen-plasma-treated polypropylene interfaces with air, water, and epoxy resins, Part II. Epoxy resins,” J. Applied Polymer Science, 42, 2045-2052, (1991).

XPS, SEM, SSIMS, FTIR-ATR, water-in-air, and air-in-water contact angle measurements have been used to unambiguously characterize the locus of failure of PP/epoxy joints. In the case of untreated PP, the fracture has been found adhesive, whereas in oxygen plasmatreated PP, it is cohesive, within bulk PP, but close to the modified PP-bulk PP interface. The smoothness of fracture surfaces allowed us to exclude mechanical interlocking effects. Shear-strength measurements showed that the mechanical strength of the joint was improved by plasma treatment. Preliminary thermal equilibration of the plasma-treated PP sample and changes in the curing cycle of the epoxy resin did not change either the locus of failure or the shear strength of the joint. The reason is probably because the number of polar functions left at the surface after thermal equilibration is sufficient to induce adhesion. The mechanical strength of the PP surface layer may be the determining factor. Fracture energy calculations showed that the observed locus of failure is the same as predicted on the basis of surface energy considerations.

263. Occhiello, E., M. Morra, G. Morini, F. Garbassi, and P. Humphrey, “Oxygen-plasma-treated polypropylene interfaces with air, water, and epoxy resins, Part I. Air and water,” J. Applied Polymer Science, 42, 551-559, (1991).

Oxygen plasma treatment of polypropylene (PP) surfaces led to introduction of oxygencontaining functionalities, with consequent improvement of surface wettability. A combination of X-ray photoelectron spectroscopy (XPS), static secondary ion mass spectroscopy (SSIMS), and contact angle measurements (water-in-air and air-in-water) allowed us to characterize the behavior of the treated surface in contact with air (low-energy surface) and water (high-energy surface).

The treated surface showed the tendency to rearrange itself to minimize its interfacial energy. When contacted with air (low-energy surface), polar groups were buried away from the polymer/air interface, while in contact with water (high-energy surface) polar groups remained at the polymer/water interface.

When contacted with air, the polymer surface layer rearranged by macromolecular motions within itself, since interdiffusion with the bulk polymer seems forbidden. These motions are thermally activated and it was possible to obtain an apparent activation energy (58.1 kJ/mol) close to those reported for other vinyl polymers.


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