The effects of pH and ionic strength on the volume phase transition temperature of thermo-responsive anionic copolymer gels

Applications of thermo-responsive (TR) gels in biomedicine and biotechnoligy require modulation of their volume phase transition temperature Tc in a rather wide interval. This is conventionally performed by incorporation of hydrophilic or hydrophobic monomers in the feed. The most pronounced growth...

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Bibliographic Details
Published in:Polymer (Guilford) 2021-04, Vol.221, p.123637, Article 123637
Main Authors: Drozdov, Aleksey D., Christiansen, Jesper deClaville
Format: Article
Language:English
Subjects:
Acrylic acid
Aqueous solutions
Constitutive models
Copolymerization
Copolymers
Critical temperature
Distilled water
Equilibrium swelling
Gels
Hydrophobicity
Ionic gel
Ionic strength
Ions
Isopropylacrylamide
Itaconic acid
Mathematical models
Microgels
Monomers
pH effects
Phase transitions
Temperature requirements
Thermo-responsive gel
Transition temperature
Transition temperatures
Volume phase transition temperature
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Summary:Applications of thermo-responsive (TR) gels in biomedicine and biotechnoligy require modulation of their volume phase transition temperature Tc in a rather wide interval. This is conventionally performed by incorporation of hydrophilic or hydrophobic monomers in the feed. The most pronounced growth of Tc occurs when TR monomers are copolymerized with anionic, cationic or ampholyte monomers. The effect of ionic monomers on the volume phase transition temperature of copolymer gels is traditionally analyzed in equilibrium swelling tests in distilled water. To evaluate how pH and ionic strength of aqueous solutions affect Tc, a constitutive model is developed. Adjustable parameters are found by fitting observations on poly(N-isopropylacrylamide-co-acrylic acid) and poly(N-isopropylacrylamide-co-itaconic acid) macro- and microgels below and above their critical temperature. The ability of the model to predict Tc is validated by comparison of experimental data with results of simulation. An analytical formula is derived that describes the influence of molar fraction of comonomers, pH and molar fraction of salt in aqueous solutions on the volume phase transition temperature of TR anionic gels. [Display omitted] •Equilibrium swelling is modeled of temperature-sensitive anionic copolymer gels.•Material constants are found for P(NIPAm-AAc) and P(NIPAm-IAc) gels.•Results of simulation demonstrate good agreement with experimental data.•The effects of pH and ionic strength are studied on the volume phase transition tem-.Perature (VPTT).•An analytical expression is derived for VPTT of thermo-responsive ionic gels.
ISSN:0032-3861
1873-2291
DOI:10.1016/j.polymer.2021.123637