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Dynamic fluctuations and spatial inhomogeneities in poly(N-isopropylacrylamide)/clay nanocomposite hydrogels studied by dynamic light scattering.

Authors
Type
Published Article
Journal
The Journal of Physical Chemistry B
1520-5207
Publisher
American Chemical Society
Publication Date
Volume
110
Issue
23
Pages
11167–11175
Identifiers
PMID: 16771379
Source
Medline
License
Unknown

Abstract

The contributions of the dynamic fluctuations and the frozen-in inhomogeneities to the total light scattering intensity observed in poly(N-isopropylacrylamide)/clay nanocomposite hydrogels were analyzed by applying the nonergodic method proposed by Pusey and van Megen. Approximately 90% of the total scattering intensity corresponds to the frozen-in component. The scattering intensity of the fluctuating component is smaller by far than that of a pure clay suspension, indicating that the thermal fluctuations of the clay particles are largely suppressed upon network formation. Accordingly, the fluctuating component consists of two contributions: one due to the polymer chains and the other, smaller one representing the residual mobility of the clay particles. The latter depends on how tightly the clay particles are fixed in the network. The dynamic features of the nanocomposite hydrogels are described by two relaxation modes. The fast one is purely diffusive and can be related to a dynamic correlation length of 6-8 nm, which is similar to that of a corresponding polymer solution. The relaxation time of the slow mode varies appreciably with sample position even though the data had been treated with the nonergodic method.

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