ABSTRACT
In situ dynamic temperature mapping of photothermally heated aluminum nanoparticles (Al NPs) embedded in a fluoropolymer (THV) is achieved using fluorescent dye (rhodamine 6G). A plasmonic grating substrate enhances the dye fluorescence intensity by a factor of seven over a glass substrate, to enable image capture rates of 500 frames per second. Further, the fluorescence intensity is linearly related to temperature and reversible. Photothermal heating of embedded Al NPs using a 2380 W cm-2 incident flux produced an Al NP heating rate of 1.2 × 104 °C s-1. Localized Al NP motion was also observed and attributed to thermal expansion and melting of the polymer. Multiphysics simulation provided agreement with experimental observations, bolstering confidence in the technique. The plasmonic grating platforms were shown to significantly improve both fluorescence intensity and the photothermal heating of Al compared to glass substrates, opening a new path for fast and high-resolution in situ temperature mapping.
ABSTRACT
Plasmonic gratings facilitate a robust in situ diagnostic platform for photothermal combustion of nanoenergetic composite thin films using an optical microscope and a high-speed camera. Aluminum nanoparticles (Al NPs) embedded in a fluoropolymer oxidizer are cast onto a plasmonic grating microchip and ignited using a low-power laser. The plasmonic grating enhances both spatial resolution and sufficient photothermal coupling to combust small Al NP clusters, initiating localized flames as small as 600 nm in size. Two-color pyrometry obtained from a high-speed color camera indicates an average flame temperature of 3900 K. Scattering measurements using polarized light microscopy enabled precise identification of individual Al NPs over a large field of view, leading to 3D reconstruction of combustion events.
