Kink propagation mechanism

Information about PPV chain motion could be obtained from a vinylene labelled material PPV-d2 [89] the presence of ring motion obscures data about chain motion from measurements of PPV-c/4. The interest here was to understand the ring-flip mechanism and determine whether there might exist a particular kink-propagation mechanism for the sp hybridized chain, analogous to the three-bond motions of vinyl polymers. At ambient temperature PPV-rf2 possesses a static Pake doublet spectrum. Figure 8.7(a) shows the spectrum at 220 "C the linewidth is reduced and there is a large apparent asymmetry parameter [t] = 0.14). 

It was mentioned on page 306 (see Fig. 5.24) that, even at room temperature, a crystal plane contains steps and kinks (half-crystal positions). Kinks occur quite often—about one in ten atoms on a step is in the half-crystal position. Ad-atoms are also present in a certain concentration on the surface of the crystal as they are uncharged species, their equilibrium concentration is independent of the electrode potential. The half-crystal position is of basic importance for the kinetics of metal deposition on an identical metal substrate. Two mechanisms can be present in the incorporation of atoms in steps, and thus for step propagation ... 

In this paper, we examine the pathological behavior of cracks propagating in model brick-and-mortar structures using the interface fracture mechanics methodology described while adopting a Kn = 0 criteria for the crack kinking out of an interface. 

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