Fold length

Polyethylene grown noF from the melt or 100 -annealed subsequently so - 

The equilibrium melting 20 -temperature of extended 10 ehain crystals is 414.6 K oso 390 400 4io 

The fact that the lamellar thickness is not mainly a function of temperature, but of the degree of supercooling, expressed by - T, can also be deduced from Fig. 5.45 

Grown from Dilute Solution at the Indicated Pressures 

Toluene was used as the solvent, and the crystallization was carried out at about 25 K supercooling. 

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Fig. 5 Initial fold length L against undercooling AT = To - T for both melt- and solution-crystallized polyethylene, from different solvents [16]. Dashed line gives previous calculations (Model A [9], old model in Fig. 4), solid line shows the results from the new model in Fig. 4 after re-adjusting the energy of fusion per - CH2 - unit from E= 1.07 to E- 1.42 kcal/mol...

The melting of a crystalline-amorphous block copolymer of poly(tetrahydro-furan)-poly(isoprene) (PTHF-PI) was investigated using DSC by Ishikawa et al. (1991). They found a double melting peak, which was proposed to result from the semicrystalline structure of the crystalline PTHF layer, with less-ordered crystallites melting before those with well-ordered domains of chain-folded PTHF. Alternative explanations include fractionation of the polydisperse block copolymer or melting of crystals with different fold lengths. 

Taking the hypothetical example of a Tibetan soil near Lhasa at 4100 m, we assume in the following simulation 0.0007 cal/cm sec, and 0.3 cal/cm3 °C for k and Cv (from Hillel 1982), respectively. This yields l/e folding lengths for seasonal temperature change of plateau soils of about 150 cm. 

Thickening occurring at 78 °C from twice-folded (fold length 12 nm) to once-folded (fold length 18 nm) crystals of C294H590 and was accompanied by a complete loss of the initial crystal shape to a fine dendritic structure with 20-30 nm wide stripes of thickened material in a matrix of material with the original crystal thickness [51]. 

The barrier factor, i.e. the expression before the bracket, decreases exponentially with increasing stem length l and the driving force factor (the term in brackets) increases with l (see Fig. 6). The product G has a maximum at an l value which is considered as the kinetically determined lamellar crystal thickness in polydisperse polymers. G becomes positive at the minimum stable fold length /mjn ... 

For polymer crystals of fixed fold length l, or for alkane crystals in a given Fm form, the slope dG/d(AT) should be constant within the limited temperature interval that is accessible for measurement [20]. The expansion of the supercooling-dependent factor in brackets in Eq. 2 gives the above-... 

It is a well-known fact that the length of folds in crystal lamellae increases with temperature. Since the melting temperature (=solidification temperature) goes up as a result of the high pressure, also the fold length will increase (with the full molecular chain length as the limit). 

The first two stages observed in the folding trajectories corresponded to a fast entropic recoil of the extended polymer, followed by a cooperative collapse that reduces the length of the protein back to its folded length [10]. To further... 

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