Polymer transfer film, mechanism

This polymer has a melting point of 276 °C and is soluble in DMSO, from which clear films could be cast. A proton-transfer polymerization mechanism was suggested by Yoda and Marvel as operative in this case74, similar to that first proposed by Breslow and coworkers75 for carbonyl amides, as follows ... 

A discussion of the wear of PTFE would not be complete without some reference to PTFE composites. This has been a popular field of study simply because without fillers the wear of PTFE is normally unacceptable. A good filler will reduce transfer wear rates by up to three orders of magnitude. Various mechanisms have been proposed and the subject has been reviewed by the present author (8,9) and others (2,52). The simplest idea is that fillers wear less than the polymer when exposed at the interface. They may also suppress transfer and improve transfer film adhesion, A good deal of effort of high quality has been put into the search for chemically induced adhesion promotion at the transferred film-substrate interface but the evidence is equivocal (53,54). Chemical changes are detected but their precise contribution to the adhesion is uncertain in commercial applications. PTFE is a remarkably stable polymer to chemical attack even at sliding interfaces. 

Figure 7 indicates the amount of polymer transfer on wear that occurs as a function of a mechanical parameter, sliding speed. An examination of Figure 7 indicates that the higher the sliding speed for a polymer in contact with a metal the greater the film thickness and accordingly the amount of polymer wear. 

The optical transparency of poly(vinyl carbazole) films produced by this room temperature process appears to be quite high, although transparency decreases at high conversions. In film form, this material is useful for photoconductors, charge-transfer complexes, and electroluminescent devices. The higher polymer molecular weight typically enhances film mechanical properties [247]. 

To achieve high conductance, both reasonable conductivity and mechanical stability in a thin film form are required. Semi-crystalline polymers have superior mechanical characteristics but vastly inferior conductivity properties to those which are fully amorphous (and well above their Tg), since ionic motion does not occur in the crystalline regions. The design of an optimized electrolyte for battery use is in fact more strongly dictated by morphological considerations (which are affected by the choice of dissolved salt) than by the selection of a system containing a solute with a high cationic transference number. 

Fig. 1 Schematic description of cohesive and interfacial wear processes from the two terms non interacting model of friction (from [96]). Bulk ploughing involves the dissipation of the frictional work within a volume of the order of the cube of the contact radius. Interfacial shear corresponds to the dissipation of the frictional energy in much thinner regions and at greater energy densities. Cohesive wear processes (cracking, tearing, microcutting...) are governed by the cohesive strength of the polymer. Mechanisms such as transfer film formation correspond to interfacial wear and do not readily correlate with accessible bulk failure properties...

In the particular case of conjugated polymers, the situation can be even more complex due to the presence of both Dexter and Forster energy transfer mechanisms (the former being dominant at short distances), and the possibility of interchain energy transfer steps these are favoured in polymer solid films due to a closer proximity between chains. 

---