Novel Sulfur Polymer Material for Long Wave Infrared Applications

Abstract

Light is categorized by its wavelength. The category that is most widely studied is the one that humans can see: the visible spectrum. As a result, there are hundreds of materials used to make devices in the visible spectrum. Other categories, such as the long wave infrared regions, are less studied. There are only a handful of materials that work in this region, and they are expensive, heavy, and hard to source. As issues with tariffs arise in the global landscape, and as the need to send long wave sensors to space increases, there is a growing need for a low cost, readily fabricated infrared material. Elemental sulfur in nature exists as a ring of eight atoms; when heat is applied, the ring breaks into a chain. Since the sulfur atom is so large, its fundamental vibrational frequencies are low and therefore it cannot be optically excited at typical infrared (IR) wavelengths. Therefore, it is highly transparent in the infrared. These sulfur chains polymerize, and to stabilize them, an organic crosslinking molecule is added to the solution. To date, the ideal crosslinker identified is a norbornadiene dimer (NBD2). Increasing the amount of NBD2 increases the stability of the material, enabling it to be molded into lenses and used in photonics applications. However, the more dimer that is added, the worse the transparency is in the infrared. This thesis explores the tradeoffs between sulfur content, transparency and stability, and how to space qualify the polymer material for low size weight and power (SWAP) broadband sensor applications in payloads. My research follows the unique path of working with multiple departments at the University of Arizona as well as industry partners, all with the common goal of taking this new material and accelerating it into a production space. My goal is to take something from research and introduce it to the world in an application where it can be useful – and sulfur polymers are destined for space.