Super-folding model

Fig. 13 The super-folding model according to Sadler and Keller [85] showing the conformation of a single molecule in a solution-grown single crystal...

Spells, Keller and Sadler (1984) showed by infrared spectroscopy that 75% of the folds in solution-grown single crystals of polyethylene led to adjacent re-entry (tight folds) and that single molecules were diluted by 50% along the lIO fold plane. Both observations are consonant with the super-fold model. 

For very low degrees of super cooling, model A is postulated to predominate. The evidence for regular folding with adjacent reentry is ... 

Figure 7.22 Model for the arrangement of a single chain in a solution-grown single crystal. The molecule is located in a plane which is super-folded. ...

At higher degrees of super cooling, the fold surface, proposed in model B (Figure 8.14), is more likely. The evidence for irregular folding with adjacent re-entry is based on ... 

Belmont, A. S and Bruce, K. (1994). Visualization of Gl chromosomes—A folded, twisted, super-coiled chromonema model of interphase chromatid structure. J. Cell Biol. 127, 287-302. 

The Peierls model explains why a chain of unsaturated carbon atoms with one conduction electron per atom does not exhibit metallic properties. If all the atoms are spaced at eqnal distance, a, the basic cell in reciprocal space is the Brillouin zone in the interval -nlawave vector). With one electron per atom, the band would be half-filled and hence the chain would exhibit metallic behaviour. A periodic distortion of the chains, commensurate with the original structure, generates an -fold super-structure and reduces the Brillouin zone to -nlnaunit cell. The effect of the distortion is to open a gap at the boundaries k = n/na of the new Brilliouin zone (Figure 1.1). Therefore, if only states below the new gap are... 

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