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Energy Elasticity of Tie Molecules in Semicrystalline Polymers
Author(s) -
Špitalský Zdenko,
Bleha Tomáš,
Cifra Peter
Publication year - 2002
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/1521-3919(20020601)11:5<513::aid-mats513>3.0.co;2-w
Subject(s) - crystallinity , elasticity (physics) , materials science , polymer , amorphous solid , elastic energy , molecule , molecular dynamics , lattice (music) , elastic modulus , crystallography , moduli , thermodynamics , chemical physics , chemistry , molecular physics , computational chemistry , composite material , physics , organic chemistry , quantum mechanics , acoustics
Elastic response of the disordered phase between crystal lamellae in semicrystalline polymers is modelled on the assumption that the stress is transferred by bridging (tie) molecules. The deformation characteristics of short poly(methylene) (PM) bridges were computed by using two methods: (a) the single‐molecule loading by molecular mechanics (MM) calculations and (b) the chain‐ensemble averaging by lattice simulations. The energy elastic functions ensuing from both methods differ considerably. In MM the loading of chains containing numerous gauche defects by an external force F yields the sawtooth‐like profile of the force ( F )–length ( R ) functions brought about by the stress‐induced gauche – trans conformational transitions. The Young's moduli E of PM chains containing several gauche defects can be less than 1% of the all‐ trans value E T ; by elimination of the defects the moduli steeply increase. In contrast, the ensemble‐averaging approach gives a smooth increase of the (positive) elastic force f with chain length R and a decrease of the (negative) energy component of the elastic force f U with R . Both energy deformation mechanisms, single‐chain loading (by F ) and statistical (by f U ), are complementary and can simultaneously be operative in the interlamellar (IL) phase. Their proportion in the stretching process should depend on the chain mobility and structural homogeneity (history) of the sample, particularly on the presence of the so‐called rigid amorphous fraction in the IL phase.