Microphase structure of poly(N-isopropylacrylamide) hydrogels as seen by small- and wide-angle X-ray scattering and pulsed field gradient NMR

Krisztina László, Armel Guillermo, Andrei Fluerasu, Abdellatif Moussaïd, Erik Geissler

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

Above the lower critical solution temperature Tc (ca. 34 °C), poly(N-isopropylacrylamide) hydrogels become weakly hydrophobic and undergo microphase separation. Macroscopic deswelling, however, is extraordinarily slow, the out-of equilibrium state of the gel being conserved for many days. In this article the structure of the microphase-separated state above Tc is probed by small-angle X-ray scattering and by pulsed field gradientNMRof the protons of water, both in the water phase and in the polymer-rich phase. Above Tc the gel comprises two microphases, separated by smooth interfaces. The cavities occupied by the water phase form a connected network. The diffusion rate of the water molecules in this phase varies from one cavity to another and can be described by a Gaussian distribution. Water molecules belonging to the polymer-rich phase are also mobile, but their self-diffusion coefficient D is greatly diminished. Absence of compartmentalization of the water phase implies that the slow deswelling rate of the gel is not due to trapping of the water phase.

Original languageEnglish
Pages (from-to)4415-4420
Number of pages6
JournalLangmuir
Volume26
Issue number6
DOIs
Publication statusPublished - Mar 16 2010

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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