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A model describing the internal structure of core/shell hydrogels
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.ORCID iD: 0000-0002-0895-1180
2011 (English)In: Soft Matter, ISSN 1744-683X, Vol. 7, no 21, 10327-10338 p.Article in journal (Refereed) Published
Abstract [en]

We apply a theory to the constrained swelling of gel particles, explicitly accounting for the propagation of elastic forces through the particle. This approach, together with conventional thermodynamics of gel swelling, allows modelling of the equilibrium state of gels with properties that are spatially inhomogeneous. In our case we consider both a discrete inhomogeneity in the form of assigning different water solubilities to the core and shell domains of the particle, and a continuous inhomogeneity in allowing the density of chemical cross-links to vary gradually through the network. The model is used to understand the behaviour of temperature-sensitive poly(N-isopropyl acrylamide) core/poly(N-isopropyl methacrylamide) shell microgels investigated in an earlier experimental study. How the swelling of the core and shell is affected by the presence of each other at different temperatures is investigated and explained from a mechanical and thermodynamic perspective.

Place, publisher, year, edition, pages
2011. Vol. 7, no 21, 10327-10338 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:uu:diva-161771DOI: 10.1039/c1sm05694hISI: 000296026700065OAI: oai:DiVA.org:uu-161771DiVA: diva2:457937
Available from: 2011-11-21 Created: 2011-11-17 Last updated: 2016-04-27Bibliographically approved
In thesis
1. On the phase behaviour of hydrogels: A theory of macroion-induced core/shell equilibrium
Open this publication in new window or tab >>On the phase behaviour of hydrogels: A theory of macroion-induced core/shell equilibrium
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Colloidal macroions are known to interact very strongly with oppositely charged polyionic hydrogels. Sometimes this results in a non-uniform distribution of the macroions within the gel, a phenomenon that is not fully understood. This thesis is a summary of four papers on the development of a theory of the thermodynamics of macroions interacting with hydrogels, aimed at explaining the phenomenon of core/shell separation in spherical gels. It is the first theory of such interactions to use a rigorous approach to whole-gel mechanics, in which the elastic interplay between different parts of the gel is treated explicitly.

The thesis shows that conventional theories of elasticity, earlier used on gels in pure solvent, can be generalised to apply also to gels in complex fluids, and that the general features of the phase behaviour are the same if mapped to corresponding system variables. It is found that the emergence of shells is due to attractions between macroions in the gel, mediated by polyions. Since the shell state is unfavourable from the perspective of the shell itself, being deformed from its preferred state, there will be a hysteresis between the uptake and the release of the macroion, like already known to occur with the uptake and release of pure solvent.

Due to the elastic interplay, growth of the shell makes further growth progressively more favourable. Thus, unless there is a limited amount of macroions available the system will not reach equilibrium until complete phase transition has taken place. If the amount is limited the core/shell separation can be in equilibrium, so the volume of the solution that the gel is in contact with plays a very important part in determining the thermodynamic resting point of the system. The ability of a macroion/hydrogel to phase separate thus depends on the molecular properties whereas the ultimate fate of such a separation depends on the proportions in number between the ingoing components.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 70 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 169
polymer, polyelectrolyte, surfactant, thermodynamics, elasticity
National Category
Pharmaceutical Sciences Physical Chemistry
Research subject
Pharmaceutical Science
urn:nbn:se:uu:diva-188151 (URN)978-91-554-8565-8 (ISBN)
Public defence
2013-02-08, B42, BMC, Husargatan 3, Uppsala, 13:15 (English)
Available from: 2013-01-18 Created: 2012-12-12 Last updated: 2013-04-02Bibliographically approved

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Gernandt, JonasFrenning, GöranHansson, Per
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