Confinement of Thermoresponsive Hydrogels in Nanostructured Porous Silicon Dioxide Templates

Authors

  • E. Segal,

    1. Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0358 (USA)
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  • L. A. Perelman,

    1. Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0358 (USA)
    2. Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0411 (USA)
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  • F. Cunin,

    1. UMR ENSCM/CNRS/UMI 5618 Institut Charles Gerhardt, 8 rue de l'ecole normale, 34296 Montpellier Cedex 5 (France)
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  • F. Di Renzo,

    1. UMR ENSCM/CNRS/UMI 5618 Institut Charles Gerhardt, 8 rue de l'ecole normale, 34296 Montpellier Cedex 5 (France)
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  • J.-M. Devoisselle,

    1. UMR ENSCM/CNRS/UMI 5618 Institut Charles Gerhardt, 8 rue de l'ecole normale, 34296 Montpellier Cedex 5 (France)
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  • Y. Y. Li,

    1. Hitachi Chemical Research Center, Inc., 1003 Health Sciences Rd., Irvine, CA 92617 (USA)
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  • M. J. Sailor

    1. Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0358 (USA)
    2. Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0411 (USA)
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  • This project has been supported by the National Science Foundation (Grant# DMR-0503006). M.J.S. is a member of the Moores UCSD Cancer Center and the UCSD NanoTUMOR Center under which this research was conducted and partially supported by NIH grant U54 CA 119335. The CNRS/DREI program (call for proposal CNRS/United States 2005 #3312) is also acknowledged for financial support of scientist exchanges. The authors thank Drs. Michael P. Schwartz and Claudia Pacholski for helpful discussions, and Evelyn York of the Scripps Institution of Oceanography, Analytical Instrument Facility, Ryan Anderson of the UCSD Integrated Technology Laboratory, and Melanie L. Oakes of the Hitachi Chemical Research Center for assistance with the scanning electron microscopy.

Abstract

A thermoresponsive hydrogel, poly(N-isopropylacrylamide) (poly(NIPAM)), is synthesized in situ within an oxidized porous Si template, and the nanocomposite material is characterized. Infiltration of the hydrogel into the interconnecting nanoscale pores of the porous SiO2 host is confirmed by scanning electron microscopy. The optical reflectivity spectrum of the nanocomposite hybrid displays Fabry–Pérot fringes characteristic of thin film interference, enabling direct, real-time observation of the volume phase transition of the confined poly(NIPAM) hydrogel. Reversible optical reflectivity changes are observed to correlate with the temperature-dependent volume phase transition of the hydrogel, providing a new means of studying nanoscale confinement of responsive hydrogels. The confined hydrogel displays a swelling and shrinking response to changes in temperature that is significantly faster than that of the bulk hydrogel. The porosity and pore size of the SiO2 template, which are precisely controlled by the electrochemical synthesis parameters, strongly influence the extent and rate of changes in the reflectivity spectrum of the nanocomposite. The observed optical response is ascribed to changes in both the mechanical and the dielectric properties of the nanocomposite.

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