The effect of time and surface contact on corona treated material can be measured and evaluated. Both components cause degradation of dyne level readings of wettability. However, the most significant cause, though it can be isolated, cannot be completely eliminated. A solution to the problem is possible but requires cooperation between material producers and converters.

An absolute method for the determinalion of surface tension of liquids using the pendent drop profiles at conical tips, which has several distinct advantages, has been proposed. For systems with zero contact angle, the dimensionless governing equations for drop profiles at different conical tips have been computer-solved. and the theoretical plots of X_T and Z_T vs. their ratio, where X_T and Z_T are the dimensionless x and z coordinates of the drop profile at a plane at the conical tip perpendicular to the axis of symmetry, are statistically anaJyied to generate suitable tables for using the proposed method.

Contact angle measurements were performed for a five-ring polyphenyl ether isomeric mixture on M-50 steel in a dry nitrogen atmosphere. Two different techniques were used: (1) a tilting-plate apparatus, and (2) a sessile drop apparatus. Measurements were made for the temperature range 25 to 190°C. Surface tension was measured by a differential maximum bubble pressure technique over the range 23 to 220°C in room air. The critical surface energy of spreading (γ_c) was determined for the polyphenyl ether by plotting the cosine of the contact angle (θ) versus the surface tension (γ_LV). The straight line intercept at cos θ = 1 is defined as γ_c. γ_c was found to be 30.1 dyn/cm for the tilting-plate technique and 31.3 dyn/cm for the sessile drop technique. These results indicate that the polyphenyl ether is inherently autophobic (i.e., it will not spread on its own surface film until its surface tension is less than γ_c). This phenomenon is discussed in light of the wettability and wear problems encountered with this fluid.

Presented at the 40th Annual Meeting in Las Vegas, Nevada May 6–9, 1985

A method is described for measuring dynamic surface and interface tension. The technique is essentially a variation of the pendant drop method in which the drop is allowed to oscillate after sudden formation at the tip of a syringe. Immediately after the oscillation stops but before the drop detaches, there is an instant of rest. At this moment, the profile of the drop is obtained using high‐speed photography. The boundary tension is then calculated from the profile using established methods. The technique is demonstrated on systems consisting of aqueous solutions of sodium stearate or oleate on one hand and mineral oil or air on the other hand. Surface or interface tensions may be obtained within 0.25 to 5 s after surface formation.

Various carbon films which have been produced in plasma have been fluorinated so that their surface structures could be analysed. Every fluorinated carbon film shows a characteristic contact angle change which follows its surface structure. These samples can be classified into two groups: amorphous and crystal, from comparison of the ratios of the area due to fluorine in the C_1s peak to the total area of the C_1s peak in ESCA results.

The characterization of polymer-water interfaces by contact angle measurement is performed using water-immiscible liquids. It gives the dispersive and the nondispersive components of surface free energy as a function of functional group of copolymer hydrogels. Using the method of Rusanov, the contactangle-induced deformation of the three-phase region in our systems was examined. The systems used were poly(2-hydroxyethyl methacrylate) (HEMA), poly(2-hydroxyethyl methacrylate-methyl methacrylate) (HEMA-MMA), poly(2-hydroxyethyl methacrylate-methoxyethoxyethyl methacrylate) (HEMA-MEEMA), poly(2-hydroxyethyl methacrylate-aminoethyl methacrylate) (HEMA-AEMA), and poly(2-hydroxyethyl methacrylate-diethylaminocthyl methacrylate) (HEMA-DEAMA). The deviation of contact angle due to the surface deformation was found to be appreciable in case of poly(HEMA-AEMA) and poly(HEMA-DEAMA).

The thermodynamic nature of interfaces and of adhesion is reexamined in the light of the Lifshitz theory of the forces acting across condensed phases. A new term is proposed, γ^LW, which consists of the sum of the terms heretofore ascribed to London, Debye, and Keesom forces, LW referring to Lifshitz-van der Waals. This term and a second term γ^SR account for the entirety of two-phase interactions in nonionic systems; SR refers to short range forces. This new analysis of forces is of value in explaining some important biological and other phenomena. The rather strong attachment of hydrophilic proteins, e.g., human serum albumin (HSA) and human immunoglobulin G (IgG), to low energy surfaces, e.g., polytetrafluoroethylene (PTFE) and polystyrene (PST), while immersed in H₂O, cannot be ascribed solely to Lifshitz-van der Waals forces (LW). For instance, it can be shown that the LW interaction would give rise to a repulsion between HSA and PTFE. The short range (SR) interactions, e.g., between H₂O and HSA, are due to H-bonds, which cannot directly account for interactions with PTFE. However, the combined SR interfacial tensions between the H-bonding liquid, the biopolymer, and the low energy surface still result in a strong attraction between PTFE and HSA, immersed in H₂O. This is analogous to the behavior of a liquid-air interface (where the fact that the direct interaction between a given solute and air is zero does not preclude the solute from being preferentially attracted to the interface). This SR attraction (minus the LW repulsion) between HSA and PTFE, in H₂O, is of the same order of magnitude as the adsorption energy derived from the Langmuir isotherm obtained for this system. Analogous results are found with IgG and PTFE, and also with HSA and IgG, with PST. Desorption patterns (obtained by changing the γ^LW and γ^SR of the liquid medium) allow an insight into the degree of local dehydration (or “denaturation”) of adsorbed proteins under various conditions. It is suggested that the term interfacial forces more aptly describes the underlying mechanism than “hydrophobic interactions.”

The surface structure and properties of poly(vinyl alcohol)-poly(dimethylsiloxane), PVAL-PDMS, graft copolymers with the controlled PDMS graft chain length as well as chain distribution were studied. The surface of the graft copolymer was examined by XPS technique and was found to be covered with essentially pure PDMS graft component even in only 5 mole% siloxane unit content. The contact angle measurement was carried out with the water-in-air technique for PVAL—PDMS graft copolymers as well as the graft copolymer/PVAL homopolymer blends and the significant surface accumulation of PDMS graft component was confirmed with the graft copolymer/PVAL blend of less than 1 mole% of siloxane unit content. In contact with water, PVAL—PDMS graft copolymer surface was found to transform its surface morphology remarkably, which was noticed by the contact angle measurement with the air-in-water technique, where the contact angle of PVAL—PDMS graft copolymer surface was found to differ from that of pure PDMS—coated surface.

The relationships of the optical characteristics of monomers (refractive index and specific refraction) and the cohesion parameters of polymers (effective cohesional energy and molar volume of the repeating unit) have been analyzed. New relationships are proposed that allow the calculation of the surface energies of homo- and copolymers using refractometric data of monomers. The relationships were tested with good consistency for a number of polymers of various chemical nature.

Gas-phase derivatization has been used along with e.s.c.a. to determine corona-discharge-induced chemical species on poly(ethylene terephthalate) (PET). Dry-air and dry-nitrogen coronas were studied. We showed that: (1) if the corona discharge treatment (CDT) power level is kept low enough, few water-soluble species are created; (2) 4% of oxygen is added to the surface with dry-air corona; (3) 75% of the oxidation products are identified as hydroperoxy, epoxy, hydroxyl, carboxylic acid and isolated carbonyl species (with hydroxyl and isolated carbonyl the prevalent species). Short-term time-dependent ageing studies show a one-to-one correspondence between the decrease in hydroperoxy species and the increase in hydroxyl and isolated carbonyl moieties. Reaction sequences are proposed to explain these data. At longer times these surface populations decrease. In general, the results from nitrogen coronas and dry-air coronas are similar.

A simple model for advancing dynamic menisci of the interface between two immiscible fluids is proposed on the hypothesis that there is a monomolecular film which precedes an apparent contact line and that a frictional force due to the solid surface is balanced with the interfacial tension forces on the film. An analytical solution for dynamic contact angles on vertical and inclined solid surfaces of plates is obtained as a function of the interfacial capillary number, the static contact angle, and the parameters of Langumuir's duplex film model. An analytical solution for dynamic meniscus heights is also derived. The analytical solutions are compared with previous experimental data. The agreement between the theoretical and experimental results is found to be fairly good, average deviations being 3.8 and 12%, respectively, for dynamic contact angles and dynamic meniscus heights at the solid surface.

Ti films were deposited onto high‐density polyethylene (HDPE) samples by electron‐beam evaporation. Prior to film deposition the samples were in situ pretreated by Ar ion bombardment using a sputter ion gun. The adhesion of the films, determined as the pull strength required for film failure, was measured as a function of ion dose. HDPE substrates processed at two different temperatures were examined. The adhesion of the Ti films to HDPE samples processed at ≊150 °C increased with the ion dose to a steady‐state value corresponding to the cohesive strength of the HDPE substrate. The adhesion to the samples processed at ≊200°C increased to a maximum and then decreased for further ion bombardment to a level of the same order as that for films deposited onto as‐prepared samples. The effects of the ion bombardment upon the HDPE surface chemistry were examined by means of x‐ray photoelectron spectroscopy (XPS). The ion bombardment resulted in dehydrogenation and cross linking of the surface region and for prolonged ion bombardment, a graphitelike surface was obtained. The film/substrate interface as well as the initial Ti film growth were examined by XPS analysis. A chemical interaction which resulted in Ti–C bonds was observed at the interface. The Ti film growth followed a pronounced three‐dimensional growth mode on as‐prepared surfaces whereas the ion bombardment resulted in a change toward a more two‐dimensional growth mode. The difference in adhesion behavior for the two types of HDPE substrates was found to be due to a difference in the amounts of low molecular weight products present within the substrates. The HDPE substrates processed at ≊200°C contained larger amounts of low molecular weight products and also had a lower degree of crystallinity and a less closely packed structure compared to those substrates processed at ≊150°C. This resulted in a segregation of low molecular weight products towards the surface of substrates processed at ∼200 °C. This segregation in turn is suggested to lead to a weak boundary layer, reducing the adhesion to as‐prepared samples and to substrates exposed to a high ion dose.

The thermodynamic aspects of the evolution of surface free energy of acrylic acid grafted polyethylene films have been examined as a function of time of contact on water. The dispersive and polar components vary with time and the interfacial free energy reaches a minimal value. Two terms participate in these variations: adsorption of water molecules and reorientation of polar acrylic groups at the water-polymer interface. Irreversible process thermodynamics has been applied to these phenomena. The surface can be characterized by a phenomenological coefficient relating the orientation rate and the orientation affinity of the polar groups at the interface.

Digital image processing techniques are applied toward the determination of polymer surface tension by pendant drop measurements. Experimental values for poly(dimethylsiloxane) as a function of molecular weight and temperature correspond well with previous measurements of poly(dimethylsiloxane) surface tension, testifying to the applicability of the new technique. Current thermodynamic treatments are found to provide excellent predictions of poly(dimethylsiloxane) surface tension for molecular weights of 3900 and 75,000 at temperatures ranging from 20 to 120°C. Theories developed by K. M. Hong and J. Noolandi (Macromolecules, 14, 1223, 1981) and Y. Rabin (J. Polym. Sci. Polym. Lett. Ed. 22, 335, 1984) yield predictions within 5% of t he experimental results for the materials and conditions studied.

A systematic study was made of seven common polyolefin resin stabilizers. Surface analysis techniques were used to characterize the surfaces of films containing these additives. Films were evaluated before and after corona treatment. Results of this study showed that a surprising number of additives are surface active. In some cases these additives have a dramatic effect on the surface chemistry produced by corona treatment, yet they do not affect subsequent ink adhesion. Conversely, an additive may not significantly affect the corona treatment chemistry but yet still reduce the adhesion performance of the film product.