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Tracer diffusion in a polymer gel: simulations of static and dynamic 3D networks using spherical boundary conditions
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Algebra and Geometry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
2016 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 47, article id 475101Article in journal (Refereed) Published
Abstract [en]

We have investigated an alternative to the standard periodic boundary conditions for simulating the diffusion of tracer particles in a polymer gel by performing Brownian dynamics simulations using spherical boundary conditions. The gel network is constructed by randomly distributing tetravalent cross-linking nodes and connecting nearest pairs. The final gel structure is characterised by the radial distribution functions, chain lengths and end-to-end distances, and the pore size distribution. We have looked at the diffusion of tracer particles with a wide range of sizes, diffusing in both static and dynamic networks of two different volume fractions. It is quantitatively shown that the dynamical effect of the network becomes more important in facilitating the diffusional transport for larger particle sizes, and that one obtains a finite diffusion also for particle sizes well above the maximum in the pore size distribution.

Place, publisher, year, edition, pages
2016. Vol. 28, no 47, article id 475101
Keywords [en]
tracer diffusion, Brownian dynamics simulation, polymer network, polymer gel, spherical boundary conditions, 3-sphere, hypersphere
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-307510DOI: 10.1088/0953-8984/28/47/475101ISI: 000385445100001PubMedID: 27662260OAI: oai:DiVA.org:uu-307510DiVA, id: diva2:1048207
Available from: 2016-11-21 Created: 2016-11-17 Last updated: 2017-11-29Bibliographically approved
In thesis
1. Computer Simulations of Polymer Gels: Structure, Dynamics, and Deformation
Open this publication in new window or tab >>Computer Simulations of Polymer Gels: Structure, Dynamics, and Deformation
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents the results of computer simulation studies of the structure, dynamics, and deformation of cross-linked polymer gels. Obtaining a fundamental understanding of the interrelation between the detailed structure and the properties of polymer gels is a challenge and a key issue towards designing materials for specific purposes. A new off-lattice method for constructing a closed network is presented that is free from defects, such as looping chains and dangling ends. Using these model networks in Brownian dynamics simulations, I show results for the structure and dynamics of bulk gels and describe a novel approach using spherical boundary conditions as an alternative to the periodic boundary conditions commonly used in simulations. This algorithm was also applied for simulating the diffusion of tracer particles within a static and dynamic network, to illustrate the quantitative difference and importance of including network mobility for large particles, as dynamic chains facilitate the escape of particles that become entrapped.

I further investigate two technologically relevant properties of polymer gels: their stimuli-responsive behaviour and their mechanical properties. The collapse of core-shell nanogels was studied for a range of parameters, including the cross-linking degree and shell thickness. Two distinct regimes of gel collapse could be observed, with a rapid formation of small clusters followed by a coarsening stage. It is shown that in some cases, a collapsing shell may lead to an inversion of the core-shell particle which exposes the core polymer chains to the environment. This thesis also explores the deformation of bimodal gels consisting of both short and long chains, subject to uniaxial elongation, with the aim to understand the role of both network composition as well as structural heterogeneity on the mechanical response and the reinforcement mechanism of these materials. It is shown that a bimodal molecular weight distribution alone is sufficient to strongly alter the mechanical properties of networks compared to the corresponding unimodal networks with the same number-average chain length. Furthermore, it is shown that heterogeneities in the form of high-density short-chain clusters affect the mechanical properties relative to a homogeneous network, primarily by providing extensibility.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 69
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1596
Keywords
computer simulations, Brownian dynamics, polymer gel, microgel, spherical boundary conditions, hypersphere, core-shell, deswelling, mechanical properties, uniaxial elongation
National Category
Physical Chemistry Polymer Chemistry
Identifiers
urn:nbn:se:uu:diva-332575 (URN)978-91-513-0144-0 (ISBN)
Public defence
2017-12-19, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-11-28 Created: 2017-10-30 Last updated: 2018-03-07

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