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Application of small system thermodynamics to polymer molecules. III. Molecular fractionation and tertiary nucleation
Author(s) -
Lindenmeyer P. H.,
Beumer H.,
Hosemann R.
Publication year - 1979
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760190109
Subject(s) - nucleation , thermodynamics , materials science , crystallization , crystal (programming language) , polymer , molecule , gibbs free energy , surface energy , thermodynamic equilibrium , melting point , atmospheric temperature range , chemical physics , crystallography , chemistry , organic chemistry , physics , computer science , composite material , programming language
The statistical mechanical methods developed in Parts I and II in this series permit the postulation of a thermodynamic criterion for the molecular fractionation which occurs during crystallization. Using this criterion we define a “local equilibrium” melting temperature as that temperature at which a polymer molecule (considered as a small thermodynamic system) has the same free energy when crystallized into the lowest possible free energy conformation on a given crystal surface (or surfaces) as it does in a completely molten state but still in contact with the same surfaces. This temperature will be a function not only of molecular length but also of the nature of the crystal surfaces to which it is exposed. Lowest “local equilibrium” melting temperatures occur on large flat crystal surfaces (secondary nucleation sites), higher temperatures result from the intersection of two crystal surfaces (tertiary nucleation sites). A number of such potential tertiary nucleation sites have been investigated and the resulting temperatures satisfactorily cover the range over which molecular fractionation has been observed.