Light-
and humidity-responsive chiral nematic photonic crystal
(PC) films containing cellulose nanocrystals (CNCs) were fabricated.
A photoactive polymer with hydrophilic groups, poly-(3,3′-benzophenone-4,4′-dicarboxylic
acid dicarboxylate polyethylene glycol) ester, was coassembled with
CNCs to form flexible iridescent films with a tunable chiral nematic
order. In the coassembly process, the intermolecular hydrogen bonds
of CNCs were weakened, which facilitated the fine regulation of the
chiral PC nanostructure. The PC films displayed sensitive responses
to both light and humidity. With increasing humidity from 30 to 100%,
the chiral nematic helix pitch increased from 328 to 422 nm. The color
of the PC films changed from blue to green, yellow, orange, and dark
red with increasing relative humidity. Over 15 min of light irradiation,
the absorption intensity of the films increased gradually. The light
and humidity responses of the films were reversible. The films maintained
their variable cholesteric liquid crystal texture and helical lamellar
structure after light irradiation at different humidities. These PC
films are expected to be useful in intelligent coatings and 3D printing.
Here, this study reports a novel confined-space thermal dewetting strategy for the fabrication of Au nanocups with tunable diameter, height, and size of cup opening. The nanocup morphology is defined by the cup-shaped void space created by a yolk-shell silica template that spontaneously takes an eccentric configuration during annealing. Thermal dewetting of Au, which is sandwiched between the yolk and shell, leads to the desired nanocup morphology. With strong scattering in near infrared, the Au nanocups exhibit superior efficiency as contrast agents for spectral-domain optical coherence tomography imaging. This confined-space thermal dewetting strategy is scalable and general, and can be potentially extended to the synthesis of novel anisotropic nanostructures of various compositions that are difficult to produce by conventional wet chemical or physical methods, thus opening up opportunities for many new applications.
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