Polymer-metal contact depth

From a more fundamental point of view, the selection of different inden-ter geometries and loading conditions offer the possibility of exploring the viscoelastic/viscoplastic response and brittle failure mechanisms over a wide range of strain and strain rates. The relationship between imposed contact strain and indenter geometry has been quite well established for normal indentation. In the case of a conical or pyramidal indenter, the mean contact strain is usually considered to depend on the contact slope, 0 (Fig. 2a). For metals, Tabor [32] has established that the mean strain is about 0.2 tanG, i.e. independent of the indentation depth. A similar relationship seems to hold for polymers although there is some indication that the proportionality could be lower than 0.2 for viscoelastic materials [33,34], In the case of a sphere, an... 

Polymer networks such as epoxies play an increasing role as adhesives in industry. Two properties are of special importance for their application (a) a strong adhesive bond is required between the solidified adhesive and the bonded object, which is often a metal (b) the mechanical stiffness of the adhesive has to be adapted to the desired level. As a consequence, the adhesive has to be selected according to its adhesion properties as well as its mechanical properties. Several studies have shown that both properties are linked as soon as the epoxy polymer layer is sufficiently thin the contact of the polymer with the substrate may induce in the polymer a broad interphase where the morphology is different from the bulk. Roche et al. indirectly deduced such interphases, for example from the dependence of the glass transition temperature on the thickness of the polymer bonded to a metal substrate [1]. Moreover, secondary-ion mass spectroscopy or Auger spectroscopy provided depth profiles of interphases in terms of chemical composition, which showed chemical variations at up to 1 pm distance from the substrate. 

There was one significant exception to this rule that was reported in a paper by Nakao and Yamada, who demonstrated small intensity enhancements in the ATR spectra of polymers that were in contact with layers not only of silver but also of nickel, platinum and palladium that had been vapor-deposited on the plane surface of a single-reflection hemispherical IRE. Unfortunately, the polymer films they studied were thicker than the depth of penetration of the uncoated IRE so the polymer molecules that were more than a few monolayers from the surface of the IRE contributed fairly strongly to the spectrum. As a result the band intensities that were measured with metal coated IREs were increased by less than a factor of two relative to the same sample in contact with an uncoated IRE and this paper was largely ignored by other workers in this field. 

Melt thermocouples are also used. These devices are made to contact the actual flowing polymer. This information can be the most useful temperature data from an extruder because it is the polymer temperature that is most important, not the metal temperature. One common type is a flush-mounted probe that has a sensor diaphragm mounted along the inside barrel surface, usually at the head end of the barrel. This type only reads the temperature of the melt in contact with the barrel, usually the same temperature as the barrel itself. Because the temperature of the melt away from the barrel may differ by over 30 °F from the surface temperature, some extruders have a more useful immersion thermocouple that penetrates further into the melt stream. This type can be designed to traverse to various depths. 

Depth concentration measurement is an important application of surface analytical methods. Examples are depth distribution of additives in plastics, or interface analysis where polymers are in contact with metals or ceramics. All surface methods with a good depth resolution (XPS, AES, SIMS) are suitable for depth or profile measurements. Complete multilayer coating systems require analytical methods that are applicable to small sample sizes and low concentrations. Techniques for obtaining chemical composition and component distribution depth profiles for automotive coating systems, both in-plane (or slab) microtomy and cross-section microtomy, include /xETIR, /xRS, ToE-SIMS, optical microscopy, TEM, as well as solvent extraction followed by HPLC, as illustrated by Adamsons et al. [5]. Surface and interface/interphase analysis can now be done routinely on both simple monolayer coatings and complex multicomponent, multilayered... 

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