Polymer Lenses Could Lower IR Detection Costs for Consumer Products

A team led by University of Arizona materials scientist Jeffrey Pyun is using a sulfur-based polymer made from waste generated by fossil fuels to develop consumer-grade infrared (IR) plastic lenses. The team has refined this material, which it first used in 2014, to create its second generation of IR lenses.

The new polymers are stronger and more temperature-resistant than the first-generation sulfur plastic developed in 2014, which was transparent to mid-IR wavelengths. The new lenses are transparent to a wider spectral window, extending into the longwave IR, and are far less expensive than the current industry standard of metal-based lenses made of germanium, a heavy, rare, and toxic material.

To strengthen the material without impeding its transparency, the researchers used computational simulations to design organic molecules that were not IR-absorbing and to predict their transparency. The inclusion of organic molecules, while adding needed strength to the sulfur-based material, could also reduce the lens’s transparency since nearly all organic molecules absorb light in the IR-fingerprint region. “It could have taken years to test these materials in the laboratory, but we were able to greatly accelerate new materials design using this method,” researcher Tristan Kleine said.

Using computational methods for their molecular-design approach, the researchers prepared chalcogenide hybrid inorganic/organic polymers (CHIPs) with enhanced LWIR transparency and thermomechanical properties via inverse vulcanization of elemental sulfur with new organic co-monomers.

Paper lead author and University of Arizona graduate student Tristan Kleine demonstrates the lens’s transparency to infrared light. Courtesy of Mikayla Mace.

Because of their chemical composition, the sulfur polymer lenses can be shaped at a much lower temperature. “A major advantage of these new sulfur-based plastics is the ability to readily process these materials at much lower temperatures than germanium into useful optical elements for cameras or sensors, while still maintaining good thermomechanical properties to prevent cracking or scratches,” Pyun said. Optical scientist Robert Norwood said that the reliability of the new lenses is essentially equivalent to the optical polymers used for eyeglasses.

While IR imaging technology is used extensively for military applications such as night vision, the cost of the technology has limited high-volume production for use in the consumer and transportation sectors. The new lens material could make IR cameras and sensor devices more accessible for use in autonomous vehicles and in-home security devices. The team is partnering with Tech Launch Arizona to translate the research into a viable technology.

A sample of the polymer material. Courtesy of Mikayla Mace.

“As we think about the Internet of Things and human-machine interfaces, the use of IR sensors is going to be a really important way to detect human behavior and activity,” Pyun said.

The research was published in Angewandte Chemie (https://doi.org/10.1002/ange.201910856).