Preparation and Characterization of a pH- and Thermally Responsive Poly(N-isopropylacrylamide-co-acrylic acid)/Porous SiO2 Hybrid

Authors

  • Loren 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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  • Troy Moore,

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

    1. Department of Bioengineering University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0412 (USA)
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  • Michael J. Sailor,

    Corresponding author
    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)
    3. Department of Bioengineering University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0412 (USA)
    • Department of Chemistry and Biochemistry University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0358 (USA).
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  • Ester Segal

    Corresponding author
    1. Department of Biotechnology and Food Engineering Technion—Israel Institute of Technology Haifa 32000 (Israel)
    2. The Russell Berrie Nanotechnology Institute Technion—Israel Institute of Technology Haifa 32000 (Israel)
    • Department of Biotechnology and Food Engineering Technion—Israel Institute of Technology Haifa 32000 (Israel).
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Abstract

A multifunctional nanohybrid composed of a pH- and thermoresponsive hydrogel, poly(N-isopropylacrylamide-co-acrylic acid) [poly(NIPAM-co-AAc)], is synthesized in situ within the mesopores of an oxidized porous Si template. The hybrid is characterized by electron microscopy and by thin film optical interference spectroscopy. The optical reflectivity spectrum of the hybrid displays Fabry–Pérot fringes characteristic of thin film optical interference, enabling direct, real-time observation of the pH-induced swelling, and volume phase transitions associated with the confined poly(NIPAM-co-AAc) hydrogel. The optical response correlates to the percentage of AAc contained within the hydrogel, with a maximum change observed for samples containing 20% AAc. The swelling kinetics of the hydrogel are significantly altered due to the nanoscale confinement, displaying a more rapid response to pH or heating stimuli relative to bulk polymer films. The inclusion of AAc dramatically alters the thermoresponsiveness of the hybrid at pH 7, effectively eliminating the lower critical solution temperature (LCST). The observed changes in the optical reflectivity spectrum are interpreted in terms of changes in the dielectric composition and morphology of the hybrids.

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