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Collapse Dynamics of Core-Shell Nanogels
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: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 49, no 15, p. 5740-5749Article in journal (Refereed) Published
Abstract [en]

Stimuli-responsive core shell nanogels display collapse properties which are determined by both the core and the shell. We examine the equilibrium properties and the detailed structural changes during a collapse transition of polymer core shell nanoparticles using Brownian dynamics simulations. Gel particles with randomly distributed cross-linking nodes are created. The influence of the cross-linking degree, core/shell mass ratio, and the strength of the interparticle attractive interaction on the collapse behavior is investigated. Both collapsed core and collapsed shell structures are considered and compared with collapsed homopolymer networks. The transition time was found to be reduced with increasing cross-linking degree and inversely related to the depth of the Lennard-Jones potential. Similar to the kinetics of single chain collapse, there is an initial formation of clusters, in this case near cross-linking nodes, and a subsequent coarsening to form a compact globule. Where the nanogels were collapsed into a compact core, the deformation was found to be essentially symmetric, with a significantly slower relaxation time for the shell units compared to the core collapse transition time. Reducing the core size, the shell units were less affected by the presence of a collapsing core. For the system with a collapsing shell, our simulations reveal in some cases an inversion, with the shell compressing and eventually squeezing out the core units. This effect was more pronounced with decreasing cross-linking degree and core/shell mass ratio.

Place, publisher, year, edition, pages
2016. Vol. 49, no 15, p. 5740-5749
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-303278DOI: 10.1021/acs.macromol.6b01206ISI: 000381320300043OAI: oai:DiVA.org:uu-303278DiVA: diva2:971354
Available from: 2016-09-16 Created: 2016-09-15 Last updated: 2017-11-21Bibliographically 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
Keyword
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: 2017-11-28

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