Effect of the Hofmeister anions upon the swelling of a self-assembled pH-responsive hydrogel

Joshua M.G. Swann, Wim Bras, Paul Topham, Jonathon R. Howse, Anthony J. Ryan

Research output: Contribution to journalArticle

Abstract

We report the effect of a range of monovalent sodium salts on the molecular equilibrium swelling of a simple synthetic microphase separated poly(methyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate)-block-poly(methyl methacrylate) (PMMA88-b-PDEA223-b-PMMA88) pH-responsive hydrogel. Sodium acetate, sodium chloride, sodium bromide, sodium iodide, sodium nitrate and sodium thiocyanate were selected for study at controlled ionic strength and pH; all salts are taken from the Hofmeister series (HS). The influence of the anions on the expansion of the hydrogel was found to follow the reverse order of the classical HS. The expansion ratio of the gel measured in solutions containing the simple sodium halide salts (NaCl, NaBr, and NaI) was found to be strongly related to parameters which describe the interaction of the ion with water; surface charge density, viscosity coefficient, and entropy of hydration. A global study which also included nonspherical ions (NaAce, NaNO3 and NaSCN) showed the strongest correlation with the viscosity coefficient. Our results are interpreted in terms of the Collins model,(1) where larger ions have more mobile water in the first hydration cage immediately surrounding the gel, therefore making them more adhesive to the surface of the stationary phase of the gel and ultimately reducing the level of expansion.
LanguageEnglish
Pages10191-10197
Number of pages7
JournalLangmuir
Volume26
Issue number12
DOIs
Publication statusPublished - 15 Apr 2010

Fingerprint

Hydrogel
Hydrogels
swelling
Anions
Swelling
Negative ions
Salts
Gels
Sodium
sodium
Polymethyl Methacrylate
anions
Hydration
gels
salts
polymethyl methacrylate
Viscosity
Ions
Sodium Iodide
expansion

Keywords

  • chemistry
  • Hofmeister anions
  • hydrogel

Cite this

Swann, Joshua M.G. ; Bras, Wim ; Topham, Paul ; Howse, Jonathon R. ; Ryan, Anthony J. / Effect of the Hofmeister anions upon the swelling of a self-assembled pH-responsive hydrogel. In: Langmuir. 2010 ; Vol. 26, No. 12. pp. 10191-10197.
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Effect of the Hofmeister anions upon the swelling of a self-assembled pH-responsive hydrogel. / Swann, Joshua M.G.; Bras, Wim; Topham, Paul; Howse, Jonathon R.; Ryan, Anthony J.

In: Langmuir, Vol. 26, No. 12, 15.04.2010, p. 10191-10197.

Research output: Contribution to journalArticle

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