We have formulated a quantitative definition of wear different from the current imprecise definitions. Wear is defined as the unwanted loss of solid material from solid surfaces due to mechanical interaction. The debris method currently used to quantify wear produces results strongly dependent on conditions. We have performed multiple scratch tests for a variety of polymer samples: polypropylene, polytetrafluoroethylene and a polyester. In each of the materials studied, the scratch penetration depths reach a constant value at a given force after 8 scratches or so. Similarly, the scratch recovery (final, healing) depths for a fixed force reach a plateau after a dozen or so scratch tests. Thus, strain hardening by repetitive scratching takes place. A likely explanation is formation of a more ordered phase - as seen before in mechanical tests by Siegmann, Aharoni, Faitelson et al. Given these results we define a measure of wear W(F) for a given indenter geometry and force F as W(F) = limn→∞ Rh(F) where n is the number of tests performed and Rh is the final (residual, healing) depth after viscoelastic recovery. The present results confirm also our earlier ones that scratch recovery is another useful way to characterize viscoelasticity.

We studied wear resistance in sliding by multiple scratching along the same groove for a variety of thermoplastics: polystyrene, styrene-acrylonitrile, polyamide 6 and polysulfone. Constant-load experiments were carried out with a micro scratch tester for several loads between 2.5 and 15 N; each time 15 scratches were performed. Except for polystyrene, all materials show an asymptotic residual depth as a function of the number of scratch tests performed. In contrast to other materials, polystyrene exhibits brittleness and debris formation. Scanning electron microscopy and scanning probe microscopy were used to characterize the deformation and wear mechanisms and were connected to the wear data obtained by multiple scratching. At 15 N we found a viscoelastic recovery for polystyrene of 27.8% while for polyamide 6 the corresponding value is 80.2%.

Contact angles of free liquids on solid samples were measured and the van Oss-Good method was applied for evaluating surface tensions of the solids. A parachor method was used for comparison: in this case the respective values were calculated for the polymer solids from molecular and group contributions. Surface tensions were computed from the parachors and the two methods compared. Effects of varying the fluoropolymer added to the epoxy before curing are discussed. For a given fluoropolymer, effects of changing its concentration on surface tension have also been evaluated and compared to the changes in scratch resistance (scratch penetration depth, recovery depth) and in static and dynamic friction. Morphological and phase structure changes are reflected in all these properties, showing a strong connection between the surface tension and tribological properties.

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Summary: Thermophysical properties and molecular relaxations in aromatic amine‐cured diglycidyl ether of bisphenol‐A (DGEBA) epoxy oligomer and poly(ethylene oxide) (PEO) mixtures were determined by DSC and dielectric techniques (TSC, DRS). The binary blends were judged to be fully miscible in the amorphous state (wPEO < 40 wt.‐%), as evidenced by the single composition‐dependent glass transition temperatures Tgs. In the amorphous blends, negative deviations of dielectric/thermal Tg‐estimates from the linear mixing rule or the behavior predicted by the Fox equation reveal weaker intermolecular interactions, compared to strong self‐association of hydroxyls in the cured thermoset. Morphological changes in PEO‐rich blends (wPEO ≥ 40 wt.‐%) are in accordance with their complicated interface structure, previously reported to consist of amorphous PEO regions, branched epoxy resin chains and an imperfect epoxy resin network located between PEO lamellae. In these blends, PEO crystallites exert steric hindrances in the amorphous regions, causing strong Tg upshifts. Changes in the relaxation dynamics of glyceryl segments (e.g., in the activation energy barrier and relaxation strength) are in accordance with the idea that the close matching between the molecular polarities of PEO, epoxy resin and the cure agent significantly contributes to the observed miscibility.