Optical and Mechanical Properties of Photoassisted, Self-assembled Nanoparticle Films

ABSTRACTThis paper presents research funded under the Defense Advanced Research Projects Agency (DARPA) MetaMaterials program for design and development of nanoparticle based, mesoscale electromagnetic and optical materials. Specifically, we present results of formulation and near infrared measurement-model validation for photoassisted, self-assembled multilayer metallic nanoparticle films. The multilayer films may be used as optical filters and absorbers. We demonstrate that nanoparticles can be formed in advanced polymer films that exhibit new electromagnetic constitutive properties. Metal nanoparticle films are produced from a single homogeneous resin containing a soluble precursor. Films cast from doped resins are exposed to UV radiation followed by a controlled thermal cure. The combination of UV exposure and thermal curing creates a multiphase material composed of low volume fractions of dispersed metallic Pd clusters (10–20 nm in size) and high concentrations of Pd nanoparticles which form surface and embedded metallic layers in the films. The layer separation is a function of UV exposure. These materials show significant absorption in the optical and near IR region of the spectrum. Furthermore, these films exhibit mechanical properties similar to bi-metallic layers, specifically, the films display reversible bending with exposure to light and an accompanying rapid temperature increase. This paper presents formulation processes, optical-mechanical measurements and measurement model comparison.