Distribution of phenols in thermoresponsive hydrogels

Katalin Kosik, Erzsébet Wilk, Erik Geissler, K. László

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

The effect of three hydrotropic molecules, phenol, resorcinol and phloroglucinol, on the thermodynamic equilibrium and the dynamics of poly(N-isopropylacrylamide) (PNIPA) hydrogels is reported. With increasing hydroxyl number of this molecular sequence both the depression of the temperature and the width of the volume phase transition (VPT) increase, reflecting the nonuniform distribution of these molecules inside the gel. Small-angle X-ray scattering detects no notable change in the local structure of the polymer chains in the presence of phenol. Dynamic light scattering observations, however, show that phloroglucinol, unlike phenol and resorcinol, produces a small but significant decrease in the mobility of the polymer in the solvent. Isothermal microcalorimetry reveals an anomalous increase in the exothermic enthalpy of mixing just below the transition, both with phenol and phloroglucinol, which indicates a pretransition state in the gel in which the aromatic molecules partly replace the bound water. This finding is corroborated by small-angle neutron scattering measurements under contrast matched conditions showing that at low phenol concentration the aromatic molecules are uniformly dispersed in the solvent, but in pretransition conditions a sparsely populated layer of phenol forms close to the polymer chains.

Original languageEnglish
Pages (from-to)2141-2147
Number of pages7
JournalMacromolecules
Volume40
Issue number6
DOIs
Publication statusPublished - Mar 20 2007

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Hydrogels
Phenols
Phenol
Phloroglucinol
Polymers
Molecules
Gels
Dynamic light scattering
Neutron scattering
X ray scattering
Hydroxyl Radical
Enthalpy
Phase transitions
Thermodynamics
Water

ASJC Scopus subject areas

  • Materials Chemistry

Cite this

Distribution of phenols in thermoresponsive hydrogels. / Kosik, Katalin; Wilk, Erzsébet; Geissler, Erik; László, K.

In: Macromolecules, Vol. 40, No. 6, 20.03.2007, p. 2141-2147.

Research output: Contribution to journalArticle

Kosik, Katalin ; Wilk, Erzsébet ; Geissler, Erik ; László, K. / Distribution of phenols in thermoresponsive hydrogels. In: Macromolecules. 2007 ; Vol. 40, No. 6. pp. 2141-2147.
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