Polymer nanocomposite thin film mirror for the infrared region.

Thin film metal oxide coatings have been used commercially as electromagnetic filters from the UV to infrared regions for over half a century. Deposition onto a substrate has typically been accomplished using vapor deposition techniques and more recently sol–gel methods. These coatings provide very good optical and mechanical performance when applied to substrates with similar thermal and mechanical properties. When conventional metal oxide coatings are applied to flexible, relatively soft substrates such as polymers, mismatches in mechanical properties can reduce interfacial adhesion or accelerate mechanical failures. The authors recently showed that a thin filmpolymer nanocomposite can be applied to a polymer substrate and maintain adhesion even under high strains. This paper describes the first time demonstration of an IR mirror using a relatively inexpensive method to apply complicated thin film dielectric stacks to a polymer substrate that can function effectively in high strain systems. Ultrathin layers of polymer nanocomposites can be used to develop electromagnetic filters, with improved mechanical performance, on compliant substrates such as polymers. Self-assembled polymer nanocomposite thin film layers composed of UV-cured acrylates and metal oxide nanoparticles were developed as antireflective coatings for ophthalmic lenses. The primary failure mode in this application is associated with intrinsic stresses introduced during processing and thermal cycling of the plastic. Nanocomposite coatings outperform ceramic coatings on plastic substrates because the primary failures are ductile, limiting secondary cracks propagating from abrasions and thereby reducing haze. Ceramic thin films in similar studies exhibited brittle fracture, which led to secondary cracks and higher haze measurements. The use of nanoparticles at high packing densities, up to sixty percent by volume, in a polymer allows for effective refractive index engineering of discrete layers extending from the visible to infrared spectrum.