Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, new research shows.
Scientists successfully took thermal images of a person through a piece of the new plastic. By contrast, taking a picture taken through the plastic often used for ordinary lenses isn’t able to show a person’s body heat.
“We have for the first time a polymer material that can be used for quality thermal imaging—and that’s a big deal,” says Jeffrey Pyun, associate professor of chemistry and biochemistry at University of Arizona. “The industry has wanted this for decades.”
The lenses and their next-generation prototypes could be used for anything involving heat detection and infrared light, such as handheld cameras for home energy audits, night-vision goggles, perimeter surveillance systems, and other remote-sensing applications, says Robert A. Norwood, professor of optical sciences.
Smart Building Technology
The lenses also could be used within detectors that sense gases such as carbon dioxide. Some smart building technology already uses carbon dioxide detectors to adjust heating and cooling levels based on the number of occupants. In contrast to the materials currently used in infrared technology, the new plastic is inexpensive, lightweight, and can be easily molded into a variety of shapes, Pyun says.
Testing of the optical properties of the new lens materials shows they are transparent to mid-range infrared, meaning the lenses have high optical focusing power. The discovery could provide a new use for the sulfur left over when oil and natural gas are refined into cleaner-burning fuels. Although there are some industrial uses for sulfur, the amount generated from refining fossil fuels far outstrips the current need for the element.
As reported online in the journal Advanced Materials, the new plastic is transparent to wavelengths of light in the mid-infrared range of 3 to 5 microns—a range with many uses in the aerospace and defense industries. The lenses also have a high optical, or focusing, power—meaning they don’t need to be very thick to focus on nearby objects, making them lightweight.
Depending on the amount of sulfur in the plastic, the lenses have a refractive index between 1.865 to 1.745. Most other polymers that have been developed have refractive indices below 1.6 and transmit much less light in the mid-range infrared.
Pyun and colleagues reported creation of the new plastic and its possible use in lithium-sulfur batteries in 2013. He and first author Jared J. Griebel, a doctoral candidate in chemistry and biochemistry, were trying to transform liquid sulfur into a useful plastic that could be produced easily on an industrial scale.
Like Baking Cupcakes
The chemists dubbed their process “inverse vulcanization” because it requires mostly sulfur with a small amount of an additive. Vulcanization is the chemical process that makes rubber more durable by adding a small amount of sulfur to rubber.
To make lenses, Griebel poured the liquid concoction into a silicone mold similar to those used for baking cupcakes.
“You can pop the lenses out of the mold once it’s cooled,” he says. “Making lenses with this process—it’s two materials and heat. Processing couldn’t be simpler, really.”
The team’s next step is comparing properties of the new plastic with existing plastics and exploring other practical applications such as optical fibers. They have filed an international patent for the new chemical process and its application for lenses.
Researchers at Seoul National University in Korea and at University of Delaware contributed to the study. The American Chemical Society, Petroleum Research Foundation, National Science Foundation, National Research Foundation of Korea, the Korean Ministry of Education, Science and Technology, the State of Arizona Technology Research Initiative Fund, and the US Air Force Office of Scientific Research funded the research.
Source: University of Arizona. Republished from Futurity.org under Creative Commons License 3.0.
