Most polymers and inorganic materials have acidic or basic sites (or both) which can interact to enhance wettability, adsorption, charge-transfer, and adhesion. These interactions, termed “polar” in the past, are independent of dipole moments and occur only when one material has acid groups which can interact with basic groups of the other material. the presence of a third component (solvent, plasticizer, penetrant, etc.) can interfere with adsorption, charge-transfer, or adhesion if the third component has strong enough acid-base interactions with either or both components. Water, a weak acid and a weak base, tends to weaken adhesion of polymers to inorganic materials but not when these have strong acid-base interactions.

A quantitative approach to predicting the enthalpy ΔH^ab of acid-base interactions between polymers and inorganic surfaces is presented based on determining the E and C constants of Drago's correlation for polymers and inorganic surfaces. Preliminary E and C constants are presented for polymethylmethacrylate, for chlorinated polyvinylchloride, for silica surfaces and for iron oxide surfaces.

Most small-molecule organic liquids are mutually miscible and their mixtures do not form stable interfaces. Polymers are, however, usually immiscible and their mixtures form multiphase structures with stable interfaces. The dispersion, morphology, and adhesion of the component phases are affected by the interfacial energies, which thereby play an important role in determining the mechanical properties of a multiphase polymer blend. This chapter discusses interfacial energy, structure, and adhesion between polymers as related to the properties of polymer blends. It provides an overview of surface tension and interfacial tension, and discusses various theories of interfacial tension such as Antonoff's rule, theory of Good and Girifalco, theory of fractional polarity, and lattice theories. The interfacial tension varies more slowly with temperature than the surface tension and arises mainly from the disparity between the polarities of two phases. The extent of non-polar (dispersion) interaction between the two phases does not vary greatly from system to system but that of polar interactions can vary greatly. The polar interactions largely determine the magnitude of the interfacial tension. The polarity of a polymer can be calculated from the interfacial tension between the polymer and a non-polar polymer such as polyethylene, which can be regarded to be completely nonpolar. Thus, if the interfacial tension of a polar polymer against polyethylene is known, the polarity of the polar polymer can be calculated. Adhesion is the bonding or joining of dissimilar bodies, while autohesion or cohesion refers to joining of identical bodies. Several adhesion theories have been proposed. They have been a subject of much controversy. Most theories deal with the formation of the adhesive bond. The chapter reviews various factors affecting the formation and the fracture of adhesive bonds.

A thermal gradient bar has been used for convenient measurements of γ_c and dγ_c/dT in complex polymers used as film-formers. The technique yields both γ_c and its temperature variation in one experimental sequence well suited for rapid, routine applications. Surface tension data have been obtained for a styrene-acrylic terpolymer, and these have also been used to characterize the compatibility of external plasticizers for the polymer. The surface tension approach has shown that glyceryl dibenzoate, though compatible with the polymer at temperatures above ∼70°C becomes incompatible at use temperatures, and exudes to the polymer film surface. Measurements of moisture sensitivity in plasticized polymer samples have confirmed the incompatibility and illustrated one of the applications to which the gradient bar and its data generation potential may be put.

The crosslinking of an ethylene–tetrafluoroethylene copolymer by exposure to a variety of inert gas plasmas, excited by an inductively coupled radiofrequency (RF) field, has been studied. The rates for direct and radiative energy-transfer processes are determined within the framework of a kinetic model of the system and are shown to have a strong dependence on the sustaining gas, as do the average depths of penetration of the ions and metastable species. Helium is found to be the most efficient gas for the crosslinking of the outermost few monolayers whereas the crosslinking of the subsurface and bulk polymer is best effected by neon. Madelung charge potential calculations have been performed to simulate the experimentally determined x-ray photoelectron spectroscopy (ESCA) spectra to elucidate several features of the mechanisms involved.

For the authors' previous work see ibid., vol.10, p.487 (1977). Further measurements are reported on the decay of surface potential of negative corona charged polyethylene films and on the crossover effect reported earlier by Ieda and co-workers (1967). It is shown that when the duration of charging is short ( approximately 25 ms) the subsequent decay curves of surface potential are well-behaved and do not exhibit the crossover effect even though the initial surface fields are high. Experiments are also reported in which an air stream is directed along the surface of the films while corona charging. This also removes the crossover effect and is in agreement with results reported in which an air stream is directed along the surface of the films while corona charging. This also removes the crossover effect and is in agreement with results reported by Okumura (1976) for polystyrene-hexamethacrylate. It is concluded that excited molecules as well as photons produced in the corona discharge play an important role in inducing charge from surface states to enter the bulk of the polymer where they are much more mobile. This leads to rapid decay of surface potential at higher initial surface fields and the crossover effect is then observed.

Contact angles have been measured as a function of the three-phase-boundary velocity. Large velocity effects observed with other techniques were not seen using the plate method. It is possible to relate the dependence of contact angles on velocity to surface heterogeneity.

Describes a method of measuring the critical surface tension of film forming polymers and the effect of temperature on the surface tension. The method gave reliable results for polyethylene, polystyrene, and polymethyl methacrylate. Changes in polymer properties due to aging can be monitored by the method, and the effect of glass transition temperatures and the effect of plasticizers in a styrene/acrylic copolymer were also studied.

The dispersion force component of surface tension γ_S^d and the nondispersive interaction energy at the water/solid interface (or the nondispersive work of adhesion) I_SWⁿ were evaluated for poly-(tetrafluoroethylene) (PTFE), poly(vinylchloride) (PVC) and poly(methylmethacrylate) (PMMA) by the analysis of the contact angles of water drops in hydrocarbon (the two-liquid-contact-angle method). The results were compared with those obtained by the one-liquid-contact-angle method with α-bromonaphthalene and methylene iodide as probe liquids, which is the method usually adopted. The values of γ_S^d from the two-liquid method were considerably larger than those from the one-liquid method, whereas their high sensitivity to error in the measurement of contact angles was taken into account. This discrepancy may be attributed to the neglect of the surface pressure π in the one-liquid method and the π values of the liquids used on the sample solids were calculated.

A new method has been developed for calculating surface free energies of polymeric materials using a simplified solution to the Fowler equation and polarizabilities and diamagnetic susceptibilities for polymer constituent groups. Comparison of this new method with estimates from group parachors, contact angle measurements, or extrapolation of data for melts indicates generally good agreement among the different methods. Discussions are also included on the effect of limited rotation on dipolar interactions and on the proper application of Good and Girifalco's method for estimating surface free energies of solids.

Ellipsometrically determined adsorption isotherms are reported for water, bromobenzene, nitro-methane, benzene, amyl, butyl, propyl, and ethyl alcohols, carbon tetrachloride, n-octane, and n-hexane on a polished polytetrafluoroethylene surface. These are nonwetting systems, and contact angles were also measured. In addition, isotherms were determined for two wetting systems, carbon tetrachloride on oxide-coated stainless steel and n-hexane on oxide-coated chromium-plated glass. For most of the nonwetting cases, the film pressure of the adsorbed film was not negligible, and should not not be omitted in semiempirical treatments of contact angle. The isotherms may be fitted by a previously proposed potential-distortion model, the choice of parameters also giving the observed contact angle. Alternatively, the isotherms are found to be segments of a single characteristic isotherm of the Polanyi type and thus obey a corresponding state principle. This characteristic isotherm for nonwetting systems does not fit the data for the two wetting cases, and the possibility is discussed that in the nonwetting cases the adsorbed state consists of bulk-like liquid in the form of micropatches or lenses rather than as a film of uniform thickness.

The contact angle may be measured by magnifying the projected image of a sessile drop, assuming the profile is elliptical, and finding the Cartesian coordinates of selected points on the profile. By selecting groups of three such points the mean equation to the outline can be determined and thus the tangent at the observed point of contact. The method was tested using water drops on various steel surfaces and using mercury on glass. Results showed generally satisfactory agreement with those obtained using the tilting plate method and also with those obtained by other investigators who have employed analytical methods to define the drop shape. If the sessile drop shape is assumed to be a part-oblate spheroid, a minimum free-energy analysis illuminates several experimentally observed features of its shape.

The dispersion force component of surface free energy, γ, and the nondispersive interaction free energy between solid and water, I, were determined by the two-liquid contact-angle method, i.e., by the measurement of contact angles of water drops on plain solids in hydrocarbon, for commercialy available organic polymers such as nylons, halogenated vinyl polymers, polyesters, etc. A method to estimate the I values from the knowledge of the polymer composition is also proposed, on the basis of the assumption of the spherical monomer unit and the sum of interactions between functional groups and water molecules at the surface.

Plasma chemistry of polymers may be categorized into two major types of reactions as (1) surface reaction of polymers and (2) polymerization of monomers by plasma. So far as these two types of reactions are concerned, plasma is very similar to other ionizing radiation, such as ..gamma.. radiation, x radiation, UV radiation, and high-energy electron beams, which can (1) initiate polymerization of certain monomers, and create free radicals on polymer exposed, which lead to (2) crosslinking of the polymer and/or (3) degradation of the polymer, or can be further utilized as the initiation sites of (4) graft copolymerization. The characteristic features of plasma are (1) the radiation effect is limited to the surface, and the depth of the layer affected by the plasma is much smaller than that by other more penetrating radiation, and (2) the intensity at the surface is generally stronger than that by the more penetrating radiations. Therefore, plasma treatment provides an ideal means of modifying surface properties of polymers. Examples are presented and discussed.

The, nature of polymer surfaces has received increasing attention as the use of these materials, in a variety of forms, increases yearly. Modifications of polymer surfaces for adhesion, friction, and diffusion oriented appiications have necessitated a careful analysis of the surfade region morphology (surface physics) and chemical properties of the surface layer (surface chemistry). The behavior of composite structures has involved the discipline of classical fracture mechanics. The orientation of polymeric species or additives which migrate to the interface may modify the wetting characteristics and, most certainly, the frictional properties in addition to the diffusion of penetrant species beyond the boundary layer. The above topics are discussed within the framework of recent analytical and theoretical developments in surface science. The findings of these recent studies have facilitated many exciting technological advances.

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

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

A sphere in continuum model, with an internal surface, is used to relate surface tension and internal pressure. The results support the previous use of this model for polar interactions. The agreement of theory and experiment is close to that obtained with a recent lattice model.

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

The crosslinking of an ethylene–;tetrafluoroethylene copolymer by exposure to an argon plasma, excited by an inductively coupled RF field, is studied over a wide range of pressures and power loadings. The results are interpreted in terms of a two-component, direct and radiative energy-transfer model showing that the outermost monolayer crosslinks rapidly via direct energy transfer from argon ions and metastables.