An opto-mechanical nanoshell–polymer composite

. Metal nanoshells, which are nanoparticles consisting of a dielectric core surrounded by a metal shell, have an optical response dictated by the plasmon resonance. This optical resonance leads to large extinction cross-sections, which are typically several times the physical cross-section of the particles. The wavelength at which the resonance occurs depends on the core and shell sizes, allowing nanoshells to be tailored for applications. In this paper, we demonstrate how incorporating nanoshells transforms a thermoresponsivepolymer into a photothermally responsive nanoshell–polymer composite. When the thermoresponsive polymer, co-N-isopropylacrylamide-acrylamide (NIPAAm-co-AAm), is heated, the polymer undergoes a reversible decrease in volume. Pristine NIPAAm-co-AAm does not inherently absorb visible or near infrared light. However, by incorporating metal nanoshell particles with a resonance that has been placed at 832 nm into the NIPAAm-co-Aam, nanoshell–polymer composite hydrogels are fabricated. When the composite is illuminated with a diode laser at 832 nm, the nanoshells absorb light and convert it to heat. This induces a reversible and repeatable light-driven collapse of the composite with a weight change of 90% after illumination at 1.8 Wcm -2 .