Estimation of the amount of nonadjacent reentry in polymer crystallization. II. Application to once folded n-paraffins

Abstract

The methods described in the preceding paper have been used to calculate the composition of a strip of once folded molecules of n-C294H590. The fraction of cilia and of stems participating in adjacent and nonadjacent reentry were calculated as a function of undercooling in regime I. Two cases corresponding to crystallization from the melt and one corresponding to dilute solution were considered. The results are strongly dependent on the relative rates of deposition of a stem from the liquid phase and the folding and reentry of the dangling half of an already attached molecule. The rate constants for adjacent and nonadjacent reentry were taken to be the same except that nonadjacent reentry leaves a hole in the strip. The undercooling below the melting point of the extended chain crystal at which the growing strip is in equilibrium with its environment is shown to be determined by all the imperfections in the strip, and particularly by the free energy of mixing. In all cases, the fractions of adjacent and nonadjacent reentry at this equilibrium undercooling are approximately equal and the fraction of cilia is a maximum. At higher undcoolings, the fraction of adjcent reentry rises, while the fractions of cilia and nonadjacent reentry fall, the exact behavior depending on the solution concentration and hence the relative rates of stem deposition from the liquid phase and of folding. This behavior is correlated with the free energy of mixing.