Scientists “color code” webbing material for exposure to damaging UV rays

NYU Tandon School of Engineering

BROOKLYN, New York, Tuesday, August 16, 2022 —Webbing structures — from chin straps and parachute material, to space habitats — are extensively employed in engineering systems as load-bearing components. They are frequently subjected to extended ultraviolet (UV) light irradiation, which can affect their integrity and reduce their mechanical strength. Despite technological advancements in structural health monitoring, long-term UV sensing techniques for webbings remain under-developed.

A new study, led by Maurizio Porfiri, Institute Professor of Mechanical and Aerospace Engineering, Biomedical Engineering, Civil and Urban Engineering, and incoming Director of the NYU Center for Urban Science and Progress (CUSP) at the NYU Tandon School of Engineering, sheds light on an enticing solution: a photochromic nylon webbing that, because it comprises spiropyran (SP) functionalized polymers, demonstrates color variation in response to extended UV exposure with controlled, color variation over multiple time scales that is conducive to UV sensing.

The team, including Peng Zhang, former researcher in Porfiri’s group and now faculty member at Tennessee Tech, and John Ohanian, research scientist at Luna Innovations, developed a mathematical model grounded in photochemistry to interpret experimental observations, unveiling the photochromic phenomenon as a multi-step, multi-timescale photochemical process involving several chemical species offering the basis for the inference of the webbing’s color. The paper, “Spiropyran-functionalized photochromic nylon webbings for long-term ultraviolet light sensing,” is featured on the cover of Journal of Applied Physics.

In their research, the investigators found that the decay rate of the webbings’ color demonstrated a dependence on the initial concentration of the SP dye. Webbings with the lowest dye concentration maintained sensitivity for four weeks, whereas at the highest dye concentration, they exhibited sensing capability after eight weeks. Thus dye concentration could be customized to meet the lifetime of the targeted applications.

The proposed photochromic webbing and the photochemistry-based mathematical model could inform future designs of UV-sensitive structures that maintain sensitivity under weeks of continuous sunlight UV exposure.

The work was supported by the U.S. Navy.

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