X-ray photon correlation spectroscopy of dynamics in thermosensitive gels

Erik Geissler, Katalin Kosik, Andrei Fluerasu, Abdellatif Moussaïd, K. László

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Temperature-sensitive hydrogels undergo a volume phase transition (VPT) when heated above a critical temperature Tc. For the poly(N-isopropyl acrylamide) (PNIPA)-water system, Tc. = 34 °C. Below T c the gels are transparent and highly swollen. On warming above Tc they promptly turn white and start to deswell. The rate of deswelling, however, can be orders of magnitude slower than that of swelling below Tc. The unstable intermediate structure above Tc. can retain the solvent and conserve the sample volume for may days, even with millimetre-sized samples. Light scattering observations of the internal structure of these gels above Tc are precluded by their strong turbidity. Small angle X-ray scattering measurements (SAXS), on the other hand, are less subject to multiple scattering as X-rays penetrate more easily into the bulk material. Conventional (incoherent) SAXS observations reveal intense scattering from smooth internal water-polymer interfaces with an estimated surface area of about 7 m2/g in the swollen gel. The dynamics in the off-equilibrium high temperature state, investigated by X-ray photon correlation spectroscopy (XPCS), displays a relaxation rate that is linearly proportional to the wavevector q, rather than to q2 as in diffusion processes. The physical origin of this relaxation is consistent with jamming, a phenomenon that is common in other disordered systems.

Original languageEnglish
Pages (from-to)73-79
Number of pages7
JournalMacromolecular Symposia
Volume256
DOIs
Publication statusPublished - 2007

Fingerprint

Photon correlation spectroscopy
X ray spectroscopy
Gels
gels
X ray scattering
photons
scattering
spectroscopy
Hydrogels
x rays
Water
Multiple scattering
Jamming
Turbidity
Light scattering
Temperature
jamming
Swelling
turbidity
Polymers

Keywords

  • Deswelling
  • Jamming
  • Poly(N-isopropyl acrylamlde)
  • Small angle X-ray scattering

ASJC Scopus subject areas

  • Polymers and Plastics
  • Materials Chemistry

Cite this

X-ray photon correlation spectroscopy of dynamics in thermosensitive gels. / Geissler, Erik; Kosik, Katalin; Fluerasu, Andrei; Moussaïd, Abdellatif; László, K.

In: Macromolecular Symposia, Vol. 256, 2007, p. 73-79.

Research output: Contribution to journalArticle

Geissler, Erik ; Kosik, Katalin ; Fluerasu, Andrei ; Moussaïd, Abdellatif ; László, K. / X-ray photon correlation spectroscopy of dynamics in thermosensitive gels. In: Macromolecular Symposia. 2007 ; Vol. 256. pp. 73-79.
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