The surface tension of polyethylene has been measured by the ring method over the temperature range 125–193°C. Because of problems with the viscousness of the liquid polyethylene, it was found convenient to use an Instron testing apparatus instead of the usual du Nouy torsion balance. The surface tension of the polyethylene decreased from a value of 28.5 dynes/cm. at 125°C. to 23.3 dynes/cm. at 193°C. with an average temperature coefficient of −0.076 dynes/cm./°C.

The rigid‐sphere theory of liquids is shown to yield an expression for the surface tension of a one‐component liquid which is essentially identical to an expression previously derived by the author employing a qualitative approach. Such a correlation suggests that the rigid‐sphere theory of liquids approach is applicable to a wide variety of nonpolar polymeric liquids.

A stream of atomic oxygen, produced by passing oxygen at low pressure through a radio-frequency coil, was allowed to impinge on films prepared from several dozen different polymers. The flow of oxygen radicals was regulated so that the reaction temperatures were between 40 and 70°C. The rapid reactions which occurred at the polymer film–oxygen radical interface were essentially unaffected by the presence of phenolic antioxidants over a wide range of concentrations but rate of reaction was greatly affected by the structure of the polymer. Bulk properties of the polymers were unchanged because the attack by atomic oxygen is limited to the surface of the polymer. In many instances a simple ablation of the surface was observed, but in some cases, especially polyethylene and polypropylene, a highly oxidized surface layer was created. These oxidized surface layers had remarkably low contact angles with water and should be of great interest in improving adhesion and other surface-dependent properties of polymers.

A low-temperature, nonequilibrium plasmajet process for activation of polymer surfaces has been developed. A stream of oxygen is partially dissociated by a glow discharge, expanded to high velocity through an orifice into a region of lower pressure, and impinged on the desired surface. Parameters measured before and after treatment of a variety of polymers include weight, surface-bonding characteristics, and wettability. The weight loss of the polymer increases with exposure time, discharge power, and proximity to the atom source; its relation to the changes in surface properties is discussed.

Equations based on a simple model of surfaces and interfaces have been found useful for relating quantitatively several previously unrelated fields of surface chemistry {10-13). These equations introduce a new term — the London dispersion force contribution to the surface free energy (7d)—and make use of this term for the accurate calculations of surface tension, interfacial tension, contact angles, heats and free energies of immersion, heats and free energies of adsorption, and the long-range van der Waals attractive forces. The accuracy of predictions of values verifiable by experiment lead one to expect that predictions of un-verifiable quantities, such as the magnitude of attractive forces at solid-solid interfaces, are to be trusted. This approach should appeal especially to those who need to use the results of surface chemistry and would prefer to calculate from existing values rather than make new experimental determinations. It should also appeal to those teaching surface chemistry in that it relates for the first time several widely separated fields of surface chemistry. Most noteworthy is the ability to calculate heats and free energies of adsorption of gases on solid surfaces directly from measurements of surface tensions and contact angles. The calculation of the long range van der Waals attractive constant, A, from values of 7d is also very attractive.

This invention relates to the surface treatment of hollow plastic articles to provide thereon a surface receptive to inks, coatings, adhesives and the like and especially to the interior treatment of hollow containers to insure that interior coatings will adhere reliably and uniformly thereto.

This invention pertains to the surface treatment of film, and more particularly to the flame treatment of the surface of polyvinyl fluoride film whereby to enhance the ad herability characteristics of said surface.

Polyvinyl fluoride is noted for its attractive properties, and in film form possesses an unusual combination of excellent resistance to outdoor weathering exposures, a high degree of physical toughness, chemical inertness, abrasion resistance, resistance to soiling and the action of solvents as well as an amazing retention of these properties at both low and elevated temperatures. The above combination of properties not only suggests many areas of use for polyvinyl fluoride in the form of self-supporting films, but also the use of such films as the outer layers of a wide variety of laminar structures destined chiefly for outdoor use wherein the polyvinyl fluoride films serve to upgrade less functional substrates, imparting to the final structure a degree of utility not to be found solely in either film or substrate.

This invention relates to surface and interior modification of thermoplastic resinous bodies, and is particularly useful in the treatment of resin plastics which are normally non-adherent or only slightly adherent to inks, adhesives, and other coatings. The invention is particularly useful in the treatment of such substantially non-adherent plastics as polyethylene and polypropylene, but is also useful in the treatment of polyvinyl chloride, polyvinylidene chloride, and copolymers, homologues, and mixtures thereof.

The effect of surface heterogeneity on the wettability of an idealized heterogeneous surface has been studied with the aid of a digital computer. Surface heterogeneity permits the existence of a large number of metastable configurations. Contact angle hysteresis is discussed in terms of a balance between the vibrational energy of a drop and the heights of the energy barriers between allowed metastable states.

This invention relates to a novel apparatus for treating the surface of plastic articles with a corona discharge, and more particularly to an apparatus for the treatment of the surface of an article made from a hydrocarbon resin with a corona discharge in order to render the surface more readily printable, which apparatus is located on one side only of the plastic article.

Certain aspects of the adsorption theory of adhesion are developed more fully than has been done previously. The consequences of nonreciprocity of spreading are pointed out, and are used to develop a more general practical point of view with respect to the adhesive bonding of materials of low-surface free energy. The system epoxy adhesive-(nonsurface-treated) polyethylene, normally considered nonadherent, is investigated experimentally in some detail. It is shown how this system, without material modification, can be made adherent. An area of study for possible adhesives for materials of lowsurface free energy is suggested.

Adhesion of polymers was determined as a function of temperature. The influence of the bonding times and temperatures indicates that the performance is established largely by the extent of wetting at the polymer-substrate interface. Considerations based on surface free energies show that most practical systems should exhibit complete wetting at equilibrium. The problem appears to involve establishing factors which retard or preclude wetting. Low substrate surface energy, high polymer viscosity, substrate topography, selective adsorption, and coacervation may be involved.

An experimental study of the wettability of rough surfaces over an extremely wide range of roughness is described. The theoretical wettability behavior of an idealized, rough surface agrees well with that of real surfaces. The theoretically predicted minimum in the curve of receding contact angle vs. roughness, for systems of high intrinsic contact angle, is experimentally verified.

The effect of roughness on the wettability of an idealized sinusoidal surface has been studied with a digital computer. The equations of Wenzel and of Cassie and Baxter are discussed in relation to the model. The heights of the energy barriers between metastable states of a drop are seen to be of utmost importance in determining the magnitude of contact angle hysteresis.

In his opening remarks at the first symposium in this series Professor Robert Good pointed out that Galileo in the 17 century was quite likely the first investigator to observe contact angle behavior with his experiment of floating a thin gold leaf on top of a water surface. Since that time contact angle measurements have found wide application as a method for determining the energetics of surfaces. This, in turn, has a profound effect on the wettability and adhesion of liquids and coatings to surfaces.

A review of the author's investigations of the equilibrium contact angles of pure liquids on low- and high-energy solid surfaces, both bare and covered with a condensed monomolecular adsorbed film, includes the critical surface tension of wetting and the effect of homology on spreading by pure liquids, the causes of nonspreading on high-energy surfaces, and the existence and properties of autophobic liquids and oleophobic monolayers. Constitutive relationships are summarized in a table of critical surface tensions of wetting. The theory and application of the retraction method of preparing adsorbed monolayers from solution and the conditions for mixed films are presented. Studies of the wetting behavior of solutions of various surfactants and the resultant explanation of the function of a wetting agent are generalized to include nonaqueous systems. Following estimates of the reversible work of adhesion of liquids to solids, the part played by wetting in obtaining optimum adhesion by adhesives is outlined, and a fundamental explanation is given of constitutive effects in the development of strong adhesive joints. Future areas of research on wetting and adhesion are indicated.

This invention relates to a method of electrically treating polyethylene film to improve the anchorage characteristics of its exposed surface whereby various materials such as printing ink or adhesive may be firmly secured thereto. More particularly, it relates to the use of an electrically conductive treating roll coated with a phenol-formaldehyde resin, in the process of passing a polyethylene film through an electrical discharge between an electrode and a dielectrically coated conductor roll.

A simple apparatus and technique are described for measuring contact angles formed by liquid drops on solid surfaces. The procedure is a modification of one described 25 years ago by Langmuir and Schaeffer. It is based on observation of the angle at which light from a point source is reflected from a liquid drop surface at its contact point with a solid. The technique gives results the same, within experimental error, as those obtained by other investigators who used the usual “drop profile” method. The apparatus has the advantages of ease of construction and operation, ruggedness, and low cost coupled with high precision and accuracy.

The present invention relates to the surface treatment of thermoplastic tubing for the reception of protective and decorative coatings, printing inks, adhesives and the like in a manner which causes them to readily and firmly adhere thereto, and has particular reference to a method of and apparatus for improving the adherence characteristics of exterior and interior surfaces of polyethylene or the like thermoplastic tubing by the application of a high voltage electrical stress accompanied by corona discharge as the tubing is extruded in substantially continuous lengths.

The effect of varying the chemical constitution of a material on its ability to adhere may be determined to a good first approximation by the nature and packing density of the atoms or molecular radicals in the solid surface. This general conclusion was established by experiments on the wetting of liquids and solids, by the effect of the constitution of polymeric solids on friction, and by the overriding effect of monomolecular adsorbed films on adhesion. The reversible work of adhesion W sub A of a liquid to a low-energy solid can be calculated approximately from the contact angle and liquid surface tension. Both W sub A and the maximum capillary rise in pores and crevices are parabolic functions of the liquid surface tension. The resulting data are discussed in terms of surface constitutive effects, changes in W sub A and in the internal stress concentrations developed as the adhesives solidify.

In previous investigations2 the heats of fusion and heat capacities of BiCl3, BiBrs, HgCl2, CdCl2, CdBr2 and Cdl2 near the meltingpoint were measured. However, the heat contents relative to 298.15 K. were not published for these halides at the melting point. Since it recently was pointed out3 that such data would be of value, the Hm. p.—ff29S. iK increments as well as the heat capacities (assuming they are constant) of the solid salts for the same temperature range are listed in Table I.

Although the agreement between the heat content increment of this study and that of an earlier work4 for CdCl2 is poor, the present value as well as those of all the other salts except the bismuth halides are in excellent agreement with literature estimates6 (Table I). Included in Table I with the heat capacities for the temperature range 298 K. to the melting point are those values found near the melting points of the salts.