Journal of Adhesion

Lee, Lieng-Huang

doi: 10.1080/00218469808011096pmid: N/A

Abstract In this paper, we briefly discuss several ways to determine the work of adhesion and the requirements for achieving maximum adhesion and spontaneous spreading. Specifically, we will concentrate on the methodology developed by van Oss. Chaudhury and Good [5–7] for the determination of the work of adhesion and interfacial tension. Recently, Good [4] has redefined the surface interaction components γ+ and γ− as hydrogen bond acidic and basic parameters. We have related the surface−hydrogen−bond components γ+ and γ− to the Taft and Kamlet's [28, 29] linear solvation energy relationship (LSER) solvatochromic α and β parameters. We [8, 9] have found that, for water at ambient temperature, α [hydrogen-bond-donating (HBD) ability] and β [hydrogen-bond-accepting (HBA) ability] are not equal, and the ratio for the normalized α and β is 1.8. This new ratio is assumed to be equal to that of γ+ & γ− for water at 20°C. On the basis of the new ratio, we will present our recalculated surface-hydrogen-bond components for several polymers and biomaterials. This change in the ratio did not affect the total surface tension or the sign of the interfacial tension. The net improvement is in the lowering of the γ− values. These data may be useful for predicting the adhesion between an adhesive and an adherend.

Gady, B.; Reifenberger, R.; Schaefer, D. M.; Bowen, R. C.; Rimai, D. S.; Demejo, L. P.; Vreeland, W.

doi: 10.1080/00218469808011097pmid: N/A

Abstract The force needed to remove micrometer-size polystyrene particles from elastomeric substrates having Young's moduli of 3.8 and 320 MPa was measured using atomic force techniques. It was found that the removal force was approximately an order of magnitude less for the more rigid substrate than for the more compliant substrate. In both cases the removal force was independent of applied load. However, when the more compliant material was overcoated with the stiffer material, the particle removal force was found to increase with increasing pressure, with the limit at low pressure commensurate with the removal force observed for the stiffer substrate and commensurate with the more compliant material at higher pressures. The results are interpreted in terms of the penetration depth of particle asperities into the substrates.

Lambropoulos, J. C.; Hwang, S. S.

doi: 10.1080/00218469808011098pmid: N/A

Abstract Measurements of the thermal conductivity of thin dielectric films in the last ten years have established that thin film thermal conductivity may be much lower than that of the corresponding bulk solid, by as much as two orders of magnitude, and that significant interfacial thermal resistance may be present along the film/substrate interface. We review such measurements of thin film thermal conductivity and interfacial thermal resistance, and use the heat conduction equation to determine their implications for the localized heating of thermally anisotropic thin films bonded to substrates. It is found that for surface heating an equivalent isotropic film can be established and that the presence of large interfacial thermal resistance leads to a strong dependence of film thermal conductivity on film thickness, especially for thin films. A microscopic model of the film/substrate interface is used to establish the dependence of the interfacial thermal resistance on porosity along the interface.

Ahsan, Tanweer; Taylor, David A.

doi: 10.1080/00218469808011099pmid: N/A

Abstract Surface energetics of ground calcium carbonates (GCC), with or without stearic acid treatment, were determined by Inverse Gas Chromatography (IGC). The surface energy data were utilized as a predictive tool to explain the optimum coating level often needed on calcium carbonate minerals to obtain the desirable mechanical strength in filled polypropylene composites. The dispersive components of the surface energies for the uncoated carbonates were also correlated with the corresponding impact resistance data. The surface with the highest energy was found to be the least resistant while the least energetic mineral, on a comparative scale, was the most resistant to impact. It is suggested that understanding the surface energetics of finely-divided solids may be a key for the development of future mineral-filled polymer composites.

Srividya, C.; Babu, S. V.; Visser, S. A.

doi: 10.1080/00218469808011100pmid: N/A

Abstract Fluorocarbon films were deposited on type 301 stainless steel substrates from mixtures of hexafluoroethane (HFE) or hexafluoroacetone (HFA) and acetylene and argon in a radio-frequency (13.56 MHz) plasma discharge. A 10 nm thick polysilicon interlayer was deposited prior to fluorocarbon film deposition to obtain good adhesion. To prevent film failure. a-C:H layer was deposited on the polysilicon layer prior to fluorocarbon film deposition, resulting in a-C:H/fluorocarbon composite film structures. The influence of the feed gas composition on the properties of the layered structure was investigated. Surface energies of the films were calculated from the film contact angle values obtained with water and diiodomethane. The composition of the surface layer of these films was characterized using X-ray photoelectron spectroscopy (XPS). The resistance offered by these a-C:H/fluorocarbon film structures to anodic breakdown in an electrolyte containing 0.1 M NaCl and 0.1 M Na2SO4 was studied using a potentiostatic technique. The anodic current density for the coated type 301 stainless steel samples was at least 3 orders of magnitude smaller than that for the bare sample and more than an order of magnitude smaller than that observed with samples coated with only the (equally thick) a-C:H layer. The resistance offered by the layered coatings to solution penetration increased with increasing fluorine content in the films.

Kendall, K.; Liang, W.; Stainton, C.

doi: 10.1080/00218469808011101pmid: N/A

Abstract When a dispersion of fine particles is concentrated, the product can contain clumps which arise from the aggregation of the particles. There are several drivers: sedimentating, drying, filtration, forcing the particles together to produce agglomerated structures which are much larger than the primary particles. The problem of understanding this phenomenon is twofold: on the one hand, it is difficult to measure aggregates in a concentrated slurry; on the other, there is no theory to predict when aggregates should form in an apparently-stable dispersion. This paper describes a new experimental method for measuring aggregates in concentrated suspensions, showing that the aggregation phenomenon can be followed over a wide range of experimental conditions. In particular, the results show that the aggregates exist at small concentrations in ostensibly stable dispersions even before concentrating takes place. Colloids based on polymers, ceramics, biological cells and emulsions all showed this aggregation effect. We have called these aggregated structures “multiplets” to distinguish them from the more normal flocs produced by destabilising the colloid. A theory of aggregation is proposed to fit the experimental results. This theory is based on the idea that multiplets form as a consequence of small adhesion forces between particles immersed in liquid; a molecular dynamics simulation using this concept of adhesion forces is used to demonstrate the formation of multiplet material at low concentrations. The theory seeks to show how the size of multiplets should vary with adhesion and with particle concentration.

Diaz, A. F.

doi: 10.1080/00218469808011102pmid: N/A

Abstract This report summarizes some recent studies aimed at determining the role of ion transfer in contact charging in polymers. The studies were carried out using blends of polymers and ionomers or polymers and organic salts. These blends were charged by contacting with a metal surface and the contact charge which developed was related to the amount and structure of the ions in the polymer blend. A Kelvin Probe and an atomic Force Microbalance were used to determine the charge. A ion transfer model for contact charging was developed which relates the charge to the ions which are on the surface and are mobile, i.e. not covalently bonded or ion pair associated.

Cheng, Feng; Hong, Shinn-Gwo; Ho, Chi-An

doi: 10.1080/00218469808011103pmid: N/A

Abstract The adhesion properties of a thermoplastic olefin elastomer (TPO) after ozone exposure are studied with attenuated total reflection infrared spectroscopy (ATR), the lap shear test, and contact angle measurement. The ozone treatment is applied after the TPO is dip-coated with acrylic acid (AA) that is mixed with benzophenone, benzoyl peroxide (BPO), and azobisisobutyronitrile initiators. ATR spectra confirm the presence of grafted AA on TPO, the amount of which depends on the ozone exposure time and the type of initiator applied. The total surface energy, the polar component, and lap shear strength (LSS) of the grafted TPO increase with increasing ozone exposure time and also vary with the initiator. All AA-grafted TPOs have much greater LSS than the TPO without AA. The greatest LSS is obtained from the specimen grafted with AA and BPO. In addition, the small differences in surface energies and failure strains associated with the great changes in LSS obtained from various specimens implies that the nature of the grafted layer has a significant effect on the adhesion strength.

Brochard-Wyart, F.; Martin, P.

doi: 10.1080/00218469808011104pmid: N/A

Abstract We study theoretically the dewetting of a liquid film intercalated between a flat solid and a weakly crosslinked rubber. The rubber is characterised by a static shear modulus, μ0, a high frequency modulus, μ∞ (≫ μ0) and a relaxation time, τ. The film dewets by nucleation and growth of a dry contact zone (radius R(t) at time t) surrounded by a liquid rim collecting the liquid. We expect three regimes: a. at short times (R < R c1), the rubber behaves like a hard elastic solid (μ = μ∞) and the dissipation is dominated by the liquid rim. We call this fast elastic dewetting. b. at intermediate times (R c1 < R < R c2), the rubber behaves like an ultra-viscous liquid. We call this “mixed viscous dewetting” because both components dissipate. c. at long times (R > R c2) the rubber behaves like a soft solid (μ = μ0) and the liquid dissipation is again dominant. We call this slow elastic dewetting.

Syed Asif, S. A.; Pethica, J. B.

doi: 10.1080/00218469808011105pmid: N/A

Abstract Depth sensing nanoindentation can be used to study the time-dependent deformation of very small volumes of materials, contacts, and thin films. Force modulation provides a continuous measure of the contact stiffness during an indentation, and minimises the adverse effect of thermal drift which is particularly important for sub-micron samples. Most of the nanoindentation experimental work so far has been carried out at room temperature. In this paper we describe a solid-state thermoelectric heating and cooling system which gives a straightforward way to vary the temperature of both sample and tip. The capabilities of the technique are demonstrated by observing the time and temperature dependent creep properties of high purity Indium. Hardness, its strain rate dependence, the stress exponent, and the activation energy for the creep process can all be directly measured from nanometre scale contacts, and the values obtained are similar to those from bulk conventional creep testing. The technique is likely to be of particular value for polymer thin films.