A Light-Switchable Liquid Metamaterial Mirror

Abstract

We describe a metamaterial film composed of gold nanoparticles wrapped in thin thermoresponsive polymer shells. The nanoparticle shells are kept partially hydrated, so that the film acts as a ‘liquid mirror’ and shows subtle interactions due to its composite metamaterial nature. Optically heating the film collapses the polymer, increasing the gold fill fraction and raising the reflectivity. This in turn decreases the optothermal absorption, making both the reflectivity and optothermal absorption nonlinear. When the polymer collapses, the film buckles due to thermophoretic flows competing against surface tension. These interactions generate a remarkable array of dynamic behaviours. Exposing the films to light causes an insulator-to-metal transition. Defects can be healed by returning the film to the liquid phase. Laser illumination of micron-scale regions generates local dimples at low power, and sintered micro-scale tracks at high power. When microbeads are combined into these films, optical-switching results in quenching of their photoluminescence as well as the ability to manipulate their spatial position in real time.