Phase transition in poly(N-isopropylacrylamide) hydrogels induced by phenols

Krisztina László, Katalin Kosik, Cyrille Rochas, Erik Geissler

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

Poly(N-isopropylacrylamide) gels swollen at 20°C in aqueous solutions of weak aromatic acids (phenol and resorcinol) display a volume transition at aromatic acid concentrations close to 50 mM. Owing to selective solvation, phenol exhibits an excess equilibrium concentration inside the swollen gels that is 7% greater than that in the surrounding bath, while for resorcinol the excess is 20%. The elastic modulus G of the gels at small strains follows the expected behavior of standard network theory, i.e., G ∝ φ1/3, where φ is the polymer volume fraction. Dynamic light scattering measurements, in which light from the thermodynamic fluctuations is heterodyned by that from the large-scale network heterogeneities, show that the collective diffusion coefficient Dc decreases at high aromatic content, while the Rayleigh ratio of the dynamic component of the scattering intensity, Rdyn, increases. No divergence of Rdyn close to the transition is observed, however, in accord with first-order nature of the transition. Within experimental error the product DcRdyn is independent of aromatic concentration. It follows that the friction coefficient of the polymer chains is not modified in the presence of the binary solvent and that the reduction in the value of Dc is due to the reduction in the osmotic modulus of the system.

Original languageEnglish
Pages (from-to)7771-7776
Number of pages6
JournalMacromolecules
Volume36
Issue number20
DOIs
Publication statusPublished - Oct 7 2003

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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