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Small-Molecule Diffusion in Semicrystalline Polymers as Revealed by Experimental and Simulation Studies
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2010 (English)In: POLYCHAR-18 WORLD FORUM ON ADVANCED MATERIALS / [ed] Mormann, W., Weinheim: WILEY-V C H VERLAG , 2010, Vol. 298, 108-115 p.Conference paper, Published paper (Refereed)
Abstract [en]

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/(tau beta), where D-a is the diffusivity of the amorphous polymer, tau is the geometrical impedance factor and beta is a factor describing the constraining effect of the crystals on the non-crystalline phase. For a polymer with 75 wt.% crystallinity, tau beta 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. beta 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 tau was obtained as the ratio of the diffusivities of the fully amorphous and semicrystalline systems. The maximum tau obtained from these simulations is ca. ten, which suggests that beta 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 tau.

Place, publisher, year, edition, pages
Weinheim: WILEY-V C H VERLAG , 2010. Vol. 298, 108-115 p.
Series
MACROMOLECULAR SYMPOSIA, ISSN 1022-1360
Keyword [en]
diffusion, morphology, polyethylene, simulation
National Category
Other Basic Medicine
Identifiers
URN: urn:nbn:se:kth:diva-31639DOI: 10.1002/masy.201000027ISI: 000288040500015Scopus ID: 2-s2.0-78651303047OAI: oai:DiVA.org:kth-31639DiVA: diva2:405430
Conference
18th World Forum on Advanced Polymeric Materials Siegen, GERMANY, APR 07-10, 2010
Note
QC 20110322Available from: 2011-03-22 Created: 2011-03-21 Last updated: 2012-04-23Bibliographically approved
In thesis
1. Simulations of Semi-Crystalline Polymers and Polymer Composites in order to predict Electrical, Thermal, Mechanical and Diffusion Properties
Open this publication in new window or tab >>Simulations of Semi-Crystalline Polymers and Polymer Composites in order to predict Electrical, Thermal, Mechanical and Diffusion Properties
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Several novel computer simulation models were developed for predicting electrical, mechanical, thermal and diffusion properties of materials with complex microstructures, such as composites, semi-crystalline polymers and foams.

A Monte Carlo model for simulating solvent diffusion through spherulitic semicrystalline polyethylene was developed. The spherulite model, based on findings by electron microscopy, could mimic polyethylenes with crystallinities up to 64 wt%. Due to the dendritic structure of the spherulites, the diffusion was surprisingly independent of the aspect ratio of the individual crystals. A correlation was found between the geometrical impedance factor (τ) and the average free path length of the penetrant molecules in the amorphous phase. A new relationship was found between volume crystallinity and τ. The equation was confirmed with experimental diffusivity data for Ar, CH4, N2 and n-hexane in polyethylene.

For electrostatics, a novel analytical mixing model was formulated to predict the effective dielectric permittivity of 2- and 3-component composites. Results obtained with the model showed a clearly better agreement with corresponding finite element data than previous models. The analytical 3-component equation was in accordance with experimental data for nanocomposites based on mica/polyimide and epoxy/ hollow glass sphere composites. Two finite element models for composite electrostatics were developed.

It is generally recognized that the fracture toughness and the slow crack growth of semicrystalline polymers depend on the concentrations of tie chains and trapped entanglements bridging adjacent crystal layers in the polymer. A Monte Carlo simulation method for calculating these properties was developed. The simulations revealed that the concentration of trapped entanglements is substantial and probably has a major impact on the stress transfer between crystals. The simulations were in accordance with experimental rubber modulus data.

A finite element model (FEM) including diffusion and heat transfer was developed for determining the concentration of gases/solutes in polymers. As part of the FEM model, two accurate pressure-volume-temperature (PVT) relations were developed. To predict solubility, the current "state of the art" model NELF was improved by including the PVT models and by including chemical interactions using the Hansen solubility parameters. To predict diffusivity, a novel free-volume diffusion model was derived based on group contribution methods. All the models were used without adjustable parameters and gave results in agreement with experimental data, including recent data obtained for polycarbonate and poly(ether-etherketone) pressurized with nitrogen at 67 MPa.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:15
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-93519 (URN)978-91-7501-290-2 (ISBN)
Public defence
2012-04-20, F2,, Lindstedtsvägen 28, entréplan, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120420Available from: 2012-04-20 Created: 2012-04-20 Last updated: 2012-04-23Bibliographically approved

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