An opto-mechanical nanoshell-polymer composite

Metal nanoshells, which are nanoparticles consisting of a dielectric core s urrounded by a metal shell, have an optical response dictated by the plasmo n resonance. This optical resonance leads to large extinction cross-section s, which are typically several times the physical cross-section of the part icles. 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 thermorespo nsive polymer into a photothermally responsive nanoshell-polymer composite. When the thermoresponsive polymer, co-N-isopropylacrylamideacrylamide (NIP AAm-co-AAm), is heated, the polymer undergoes a reversible decrease in volu me. Pristine NIPAAm-co-AAm. does not inherently absorb visible or near infr ared light. However, by incorporating metal nanoshell particles with a reso nance that has been placed at 832 nm into the NIPAAm-co-Aam, nanoshell-poly mer composite hydrogels are fabricated. When the composite is illuminated w ith a diode laser at 832 run, the nanoshells absorb light and convert it to heat. This induces a reversible and repeatable light-driven collapse of th e composite with a weight change of 90% after illumination at 1.8 Wcm(-2).