n-alkane homogeneous nucleation: crossover to polymer behavior

H. Kraack, M. Deutsch, E. B. Sirota

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83 Scopus citations

Abstract

Homogeneous nucleation of crystallizing n-alkanes (CH3-(CH2)n-2-CH3, 17 ≤ n ≤ 60) and some low-MW polyethylene (PE) fractions were studied using calorimetry and compared to reanalyzed PE data of Ross and Frolen. The undercooling and derived surface energy of the n-alkanes starts increasing for n as low as 25, far below the low-n limit for chain-folding. This behavior appears to extrapolate to the high undercooling exhibited by high-MW PE. The behavior is discussed in terms of a possible crossover between full-molecule nuclei of low-n and 'bundle' nuclei of larger n. It is also related to the negentropic model, in that the surface energy increases when the 'cilia' dangling from the bundle nucleus exceed a length where their entropic cost begins to significantly raise the surface energy. At low n, homogeneous nucleation occurs into the metastable rotator phase whose potential importance at high n is discussed.

Original languageEnglish
Pages (from-to)6174-6184
Number of pages11
JournalMacromolecules
Volume33
Issue number16
DOIs
StatePublished - 8 Aug 2000

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