Control of gel swelling and phase separation of weakly charged thermoreversible gels by salt addition

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

Doping of thermoreversible polymer gels with charged monomers provides a way to control phase separation and gelation conditions by coupling the properties of the gel with a tunable ionic environment. We analyze the dependence of the gelation and phase separation conditions on the amount of salt present using a mean field model of weakly charged associative polymers. The ions and co-ions present are explicitly considered at the mean field level, and we determine their concentrations in the different equilibrium phases when the system undergoes phase separation. For weak polymer charge, the entropic contributions of the ions to the free energy of the system play a central role in the determination of the location of phase equilibrium. In the simplest case, when the associative interaction responsible for gel formation is independent of the electrostatic interaction, the addition of salt changes the polymer equilibrium concentrations and indirectly changes the measurable swelling of the gel. We construct phase diagrams of these systems that exhibit the location of the coexistence region, the gel-sol boundary, and the location of the tie lines. We determine the swelling of the gel within the coexistence region. Our main result is that the effect of the salt on the properties of the weakly charged gel can be described through an extra contribution to the effective immiscibility parameter % proportional to the square of the doping degree f 2 and to the inverse square of the added salt concentration s -2.

Original languageEnglish (US)
Pages (from-to)3840-3847
Number of pages8
JournalMacromolecules
Volume40
Issue number10
DOIs
StatePublished - May 15 2007

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Phase separation
Swelling
Gels
Salts
Polymers
Gelation
Ions
Phase equilibria
Doping (additives)
Polymethyl Methacrylate
Sols
Coulomb interactions
Free energy
Phase diagrams
Solubility
Monomers

ASJC Scopus subject areas

  • Materials Chemistry

Cite this

Control of gel swelling and phase separation of weakly charged thermoreversible gels by salt addition. / Solis, Francisco; Vernon, Brent.

In: Macromolecules, Vol. 40, No. 10, 15.05.2007, p. 3840-3847.

Research output: Contribution to journalArticle

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AB - Doping of thermoreversible polymer gels with charged monomers provides a way to control phase separation and gelation conditions by coupling the properties of the gel with a tunable ionic environment. We analyze the dependence of the gelation and phase separation conditions on the amount of salt present using a mean field model of weakly charged associative polymers. The ions and co-ions present are explicitly considered at the mean field level, and we determine their concentrations in the different equilibrium phases when the system undergoes phase separation. For weak polymer charge, the entropic contributions of the ions to the free energy of the system play a central role in the determination of the location of phase equilibrium. In the simplest case, when the associative interaction responsible for gel formation is independent of the electrostatic interaction, the addition of salt changes the polymer equilibrium concentrations and indirectly changes the measurable swelling of the gel. We construct phase diagrams of these systems that exhibit the location of the coexistence region, the gel-sol boundary, and the location of the tie lines. We determine the swelling of the gel within the coexistence region. Our main result is that the effect of the salt on the properties of the weakly charged gel can be described through an extra contribution to the effective immiscibility parameter % proportional to the square of the doping degree f 2 and to the inverse square of the added salt concentration s -2.

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