2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Photo, thermal, and pH responsive microgels

T. Cai, A. Garcia, M. Marquez, R. Rosario, Z. Hu, D. Gust, M. Hayes, C. Park and J. Springer
Philp Morris USA, US

Keywords:
spiropyran, microgel, poly(N-isopropylacrylamide)

Abstract:
Microgels with photo, thermal, and pH responsive properties in aqueous suspension have been synthesized and characterized using dynamic light scattering and UV-visible spectroscopy. The new route involved first preparing PNIPAM-allylamine microgels and 1’-(3-carboxypropyl)-3’3’-dimethyl-6-nitrospiro[2H-1]benzopyran-2’2’-indoline (SP). Then the carboxylic acid end group of this functionalized spiropyran was reacted with amine group in microgels to form a covalent amide linkage. The resultant PNIPAM-SP microgels in darkness underwent a volume change from a swollen state to a collapsed state above the transition temperature. Under light irradiation, the transition temperature became lower from 34 oC to 31 oC. This decrease was because irradiation of the open, hydrophilic form with light caused photoisomerization back to the closed, hydrophobic form. The PNIPAM-SP microgels are monodisperse, and can self-assemble into a crystalline lattice. The UV-visible spectra of the aqueous suspension showed both absorption peak around 515 nm, attributed to the merocyanine state in darkness, and two sharp peaks from Bragg diffraction of colloidal crystallites. The color change from SP configuration change in PNIPAM-SP microgel suspension was reversible upon alternating dark, UV and visible light irradiation.

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