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Small‐Molecule Diffusion in Semicrystalline Polymers as Revealed by Experimental and Simulation Studies
Author(s) -
Nilsson Fritjof,
Hedenqvist Mikael S.,
Gedde Ulf W.
Publication year - 2010
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.201000027
Subject(s) - crystallinity , penetrant (biochemical) , materials science , amorphous solid , thermal diffusivity , spherulite (polymer physics) , polymer , crystal (programming language) , diffusion , small angle x ray scattering , analytical chemistry (journal) , polymer chemistry , thermodynamics , crystallography , scattering , chemistry , composite material , organic chemistry , optics , physics , computer science , programming language
Summary: Diffusion of n ‐hexane in poly(ethylene‐ co ‐1‐hexene)s with 15–75 wt.% crystallinity was studied by desorption experiments analyzing data using the Fickian equations with a concentration dependent diffusivity. The effect of the impenetrable crystalline phase on the penetrant diffusivity ( D ) is described by D = D a /( τβ ), where D a is the diffusivity of the amorphous polymer, τ is the geometrical impedance factor and β is a factor describing the constraining effect of the crystals on the non‐crystalline phase. For a polymer with 75 wt.% crystallinity, τβ varied markedly with penetrant concentration ( v 1a ) in the penetrable phase: 1000 ( v 1a = 0) and 10 ( v 1a = 0.15). This penetrant‐uptake had no effect on the gross crystal morphology, i.e. β must be strongly dependent on v 1a . Samples saturated in n ‐hexane exhibited a penetrant‐induced loosening of the interfacial structure, as revealed by an increase in crystal density that require an increased mobility in the interfacial component and by a decrease in the intensity of the asymmetric X‐ray scattering associated with the interfacial component. The geometrical impedance factor has been modelled by mimicking spherulite growth and τ was obtained as the ratio of the diffusivities of the fully amorphous and semicrystalline systems. The maximum τ obtained from these simulations is ca. ten, which suggests that β in the systems with v 1a = 0.15 takes values close to unity. The simulations showed that the geometrical impedance factor is insensitive to the ratio of the crystal width and the crystal thickness. A free path length scaling parameter characteristic of the amorphous phase correlated with τ .