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Phys. Rev. E 71, 040801(R) (2005) [4 pages]

Density profiles of temperature-sensitive microgel particles

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T. G. Mason1,* and M. Y. Lin2
1Department of Chemistry and Biochemistry, and Department of Physics and Astronomy, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, California 90095 USA
2Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 USA

Received 8 November 2004; published 18 April 2005

We have performed small angle neutron scattering measurements (SANS) on dilute aqueous dispersions of polymer microgel particles as a function of temperature, T. The microgel particles are spherical crosslinked assemblies of a loose gel network of a poly-N-isopropylacrylamide (NIPAM) polymer. When the temperature is raised beyond a critical temperature, Tlc≈32 °C, the polymer becomes more strongly attracted to itself than the solvent, and the microgel particles contract. The measured form factor, F(q), for dilute suspensions of uniform microgel particles exhibits many peaks that are characteristic of solid polymer nanospheres. The position and amplitude of the peaks as a function of wave number, q, provide insight into the density profile of poly-NIPAM within the microgels. These peaks can be described well over a wide range of temperature by a model of the polymer density within the particles that is constant up to an inner radius, R1, and decreases linearly to zero at an outer radius, R2.

© 2005 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevE.71.040801
DOI:
10.1103/PhysRevE.71.040801
PACS:
61.41.+e, 61.12.−q, 61.46.+w, 83.80.Kn

*Author to whom correspondence should be addressed.

 
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