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Meso-scale modelling of composites and semi-crystalline polymers
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. (Polymera Material)
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis covers the first few steps of a multi-scale computer simulation strategy for predicting physical properties of complex polymers like composites and semi-crystalline polymers. Meso-scale simulations of crystallization and solvent diffusion in polyethylene as well as simulations examining the geometrical impact on the effective permittivity of composites have been performed. These meso-scale models will in the near future be coupled to molecular dynamics models for increased realism and accuracy.  

The first paper was focused on solvent diffusion in spherulitic semi-crystalline polyethylene. Geometrical models of polyethylene spherulites were constructed and Monte-Carlo random walker simulations were used to estimate the geometrical impedance factor as function of volume crystallinity, mean free path and other geometry properties. Novel numerical off-lattice algorithms made it possible to increase the maximum volume crystallinity from 40 to 55%, to decrease the computation time a factor 100 and to use shorter and more realistic diffusion jump-lengths. The simulation results were in good agreement with experimental results and new analytical formulas were found that could be neatly fitted to both simulation data and experimental data. It was noticed that the geometrical impedance factor was proportional to the polymers mean free path length rather than its length/width aspect ratio and that the traditional Fricke formula for oblate spheroids was not able to correctly predict the diffusion behaviour in complex geometries like spherulites at medium-high volume crystal fractions.   

The second paper was focused on the electrostatics of composites. Geometrical models of layered composites were first obtained and the finite element method was then used to calculate the effective composite permittivity as function of particle content, particle shape, degree of mixing and other geometrical issues. Analytical lamellae formulas for 2- and 3-phase composites were formulated with clearly better correlation to corresponding finite element data than all other previously known analytical formulas. The analytical 3-phase formula was successfully compared with experimental data for mica/polyimide and it was noted that the influence of water and air was significant.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , 53 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2009:54
Keyword [en]
semi-crystalline polymers, simulations, diffusion, electrostatics
National Category
Materials Engineering Computational Mathematics Polymer Chemistry
URN: urn:nbn:se:kth:diva-11296ISBN: 978-91-7415-463-4OAI: diva2:272803
Rånbyrummet, Teknikringen 56, KTH, Stockholm (Swedish)
Available from: 2009-10-19 Created: 2009-10-14 Last updated: 2010-10-27Bibliographically approved
List of papers
1. Penetrant diffusion in polyethylene spherulites assessed by a novel off-lattice Monte-Carlo technique
Open this publication in new window or tab >>Penetrant diffusion in polyethylene spherulites assessed by a novel off-lattice Monte-Carlo technique
2009 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 45, no 12, 3409-3417 p.Article in journal (Refereed) Published
Abstract [en]

Semi-crystalline polymers have a complex hierarchical structure. The purpose of this study was to mimic the real structure of polyethylene spherulites by computer simulation using an off-lattice method in order to predict their diffusion properties. The principles used to build the spherulites were based on established findings obtained by electron microscopy. Spherulites in the crystallinity range of 0-55 vol% were built. Diffusion of small-molecule penetrants assuming no interfacial trapping at the amorphous-crystal boundary was studied using a Monte-Carlo technique. The main findings were: (i) diffusion was isotropic; (ii) diffusion was independent of the aspect ratio of the crystal building bricks, clearly in disagreement with the Fricke model: (iii) the geometrical impedance factor showed a dependence on the average free path length of the penetrant molecules in the amorphous phase: and (iv) data for the geometrical impedance factor obtained by simulation compared favourably with experimental data obtained for several penetrants showing limited interfacial trapping.

Polyethylene spherulite, Off-lattice mesoscale simulation, Diffusion, Monte-Carlo model, molecular-dynamics simulation, melt-crystallized polyethylene, lamellar, morphology, isotactic polypropylene, transport-properties, free-volume, n-alkanes, organization, polymers, gases
National Category
Polymer Chemistry
urn:nbn:se:kth:diva-19054 (URN)10.1016/j.eurpolymj.2009.09.018 (DOI)000272871400011 ()2-s2.0-70449481086 (ScopusID)
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2012-04-23Bibliographically approved
2. Modelling the Relative Permittivity of Anisotropic Insulating Composites
Open this publication in new window or tab >>Modelling the Relative Permittivity of Anisotropic Insulating Composites
2011 (English)In: Composites Science And Technology, ISSN 0266-3538, Vol. 71, no 2, 216-221 p.Article in journal (Refereed) Published
Abstract [en]

Three models have been developed for predicting the dielectric permittivity of insulating composites with inclusions of different lengths (from nm and larger) and different shapes. Firstly, for approximately periodic materials, a finite element model based on a smallest repeating box method was used in order to mimic frameworks with fibres, crystals, clay platelets, foams and lamellar layers. The introduction of parameters for relative aspect ratio, overlap, rotation and packing density made the model very flexible while maintaining its simplicity. Secondly, a finite element composite model with oriented, randomly positioned particles of different shapes was constructed. Thirdly, an analytical relationship to approximate the effective permittivity of two- or three-phase insulators with brick-shaped inclusions was derived. For a wide range of volume fractions, permittivity ratios and packing conditions, this model gave solutions very close to corresponding finite element simulation data for lamellae, much closer than all the other analytical relationships found in the literature. Results obtained by simulation were in agreement with experimental data from the literature for composites of micrometre-sized hollow glass spheres in epoxy and nanocomposites of mica platelets in polyimide, provided that a third (interfacial) component was introduced.

Polymer-matrix composites (PMCs), Electrical properties, Modelling
National Category
Materials Engineering
urn:nbn:se:kth:diva-25417 (URN)10.1016/j.compscitech.2010.11.016 (DOI)000286909100020 ()2-s2.0-78650877405 (ScopusID)
Swedish Research Council, VR-05-6138
QC 20110317 Ändrad från submitted till published 20110317Available from: 2010-10-21 Created: 2010-10-21 Last updated: 2012-04-23Bibliographically approved

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