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Optical Waveguide‐Enhanced Diffraction for Observation of Responsive Hydrogel Nanostructures
Author(s) -
Pirani Federica,
Sharma Nityanand,
MorenoCencerrado Alberto,
Fossati Stefan,
Petri Christian,
Descrovi Emiliano,
TocaHerrera José L.,
Jonas Ulrich,
Dostalek Jakub
Publication year - 2017
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.201600400
Subject(s) - lower critical solution temperature , nanopillar , materials science , swelling , nanostructure , swell , nanotechnology , diffraction , optical microscope , nanoimprint lithography , optoelectronics , composite material , optics , scanning electron microscope , polymer , copolymer , fabrication , medicine , oceanography , physics , alternative medicine , pathology , geology
Optical diffraction measurements are reported for in situ observation of swelling and collapsing of responsive hydrogel nanostructures. The optical signal is enhanced by probing the surface carrying periodic arrays of hydrogel nanostructures by resonantly excited optical waveguide modes. UV‐nanoimprint lithography is employed for the preparation of the arrays of nanopillars from photo‐crosslinked N ‐isopropylacrylamide (pNIPAAm)‐based hydrogel that are covalently tethered to a gold surface. The thermo‐responsive properties of such pNIPAAm nanopillars that swell in 3D are compared to those of a thin film prepared from the identical material and that is allowed to swell predominantly in 1D. The nanopillars with a diameter of ≈100 nm and aspect ratio of 2 swell by a factor of ≈6 as determined by optical measurements supported by simulations that are compared to morphological characteristics obtained from atomic force microscopy. Bending of nanopillars above the lower critical solution temperature (LCST), erasure of the topographic structure by drying at temperature below the LCST, and recovery by subsequent swelling below the LCST and drying at temperature above the LCST are observed.