Topographic versus Lattice Matching

The first order analysis of epitaxial crystallization usually centers on the standard lattice matching criterion, namely near-matching of cell dimensions in corresponding orientations of the contact plane. This is indeed a useful test of any epitaxial crystallization. 

The epitaxial crystallization of iPP on benzoic acid is not amenable to the same in-depth analysis using diffraction data only. In that case, it is necessary to resort to AFM analysis of the iPP contact face, after dissolution of the benzoic acid substrate [32,33]. Here again, the contact face displays the four pattern of methyl groups (cf. Fig. 8.5a). It might be questioned whether a substrate that is more flat would favor the five face of odPP, that is, also less bumpy. No experimental evidence has been collected so far on this issue. 

2 Forms I and II of Syndiotactic Polypropylene sPP exists in different crystal modifications. Two of these are of interest in the present context. They are both based on a ttgg chain conformation, which gener- 

When sPP crystallizes epitaxially on 2-quinoxalinol (2-Quin) at a low temperature, the metastable Form II is obtained, as evidenced by its different, specific diffraction pattern [58]. Contrary to the monoclinic phase of PE, formation of this metastable phase is not linked with a better dimensional match. Rather, it stems from a much superior topographic match between the polymer and the substrate. The crux of the argument can be summarized in a three-part figure (Fig. 8.10). When seen from the side, the contact face of 2-Quin displays relatively long-range ridges with a periodicity that matches the c-axis repeat distance of sPP. The profiles 

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