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Brownian dynamics of a compressed polymer brush model: Off-equilibrium response as a function of surface coverage and compression rate
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
2011 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 35, 16084-16094 p.Article in journal (Refereed) Published
Abstract [en]

We study the compressive behaviour of a polymer-covered surface (i.e., a "polymer brush'') using Brownian dynamics simulations. The model consists of grafted chains with variable flexibility, variable intra-and inter-chain interactions, as well as different surface coverage. We discuss the polymer brush response to confinement by considering variable rates of compression under a hard plane. Our results show a small degree of inter-chain entanglement, regardless of whether the interaction is attractive or merely excluded volume. We observe that the molecular shape depends strongly on the surface coverage. Dense brushes exhibit a limited degree of lateral deformation under compression; instead, chains undergo a transition that produces a local patch with near-solid packing. This effect due to surface density can be undone partially by increasing the attractive nature of the chain interaction, by modulating the rate of compression, or by allowing "soft anchoring'', i.e., the possible Brownian drift of the grafting bead on the surface. We have also studied the polymer brush relaxation while maintaining the compressing plane, as well as after its sudden removal. We find evidence that also the relaxation depends on surface density; dense brushes appear to be configurationally frustrated at high compression and are unable to undergo swelling, regardless of the pressure applied.

Place, publisher, year, edition, pages
2011. Vol. 13, no 35, 16084-16094 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-158668DOI: 10.1039/c1cp21433kISI: 000294167700042OAI: oai:DiVA.org:uu-158668DiVA: diva2:440631
Available from: 2011-09-13 Created: 2011-09-13 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Brownian Dynamics Simulations of Macromolecules: Algorithm Development and Polymers under Confinement
Open this publication in new window or tab >>Brownian Dynamics Simulations of Macromolecules: Algorithm Development and Polymers under Confinement
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis I have used computer simulations to study the structure and dynamics of grafted polymers during confinement. These systems are of importance for understanding e.g. colloidal stability and surface coatings. We have used Brownian dynamics simulations with the polymers modeled as discrete wormlike chains allowing for a variable persistence length as well as different non-bonded interactions. The size and shape of the chains are characterized by the radius of gyration and the degree of oblateness/prolateness, and the entanglement is followed by calculating the mean overcrossing number. Starting in the dilute regime with a single polymer mushroom we have investigated how the rate of compression and solvent quality effects the behaviour of a compressed chain. In the brush regime, we investigated how the surface coverage effects the behaviour during compression. For low coverages the chains have the possibilty to increase their lateral extension during confinement but in general, the chains have a low inter-entanglement, as they strive to keep their integrity during the confinement process.

To go from a polymer brush to the construction of a connected network, we have developed a method to construct a closed network without using periodic boundary conditions by building the network on a sphere in R4. In this way we avoid the restrictions of periodicity at the cell boundaries. We finally also show how to develop the idea of using spherical boundary conditions, by presenting a novel algorithm for simulating diffusion on a spherical surface. The method is more stable and allows for larger time steps, compared to commonly used methods in computer simulations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 937
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-173435 (URN)978-91-554-8377-7 (ISBN)
Public defence
2012-06-04, Å2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2012-05-14 Created: 2012-04-24 Last updated: 2014-12-30Bibliographically approved

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Elvingson, Christer

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