Photochemical Control of Burn Rates in Nitrocellulose Polymer Films

The control of burn rates for energetic materials is critical for improving performance, safety, and adaptability in propulsion systems. This study investigates whether photochemically reactive molecules can modify the burn rate of a prototypical energetic polymer, nitrocellulose (NC) . Molecules from the hexaarylbiimidazole, spiropyran, and diarylethene photochrome families are dissolved in solid NC , and high‐speed imaging is used to measure flame propagation velocities before and after photoisomerization. Only the hexaarylbiimidazole derivative o‐Cl‐HABI gives rise to a significant change in the burn rate. The enhancement increases with o‐Cl‐HABI concentration, which is varied from 0.001 to 0.1 M. At a concentration of 0.1 M, the burn front velocity increases by 3× relative to pristine NC , and by 4.5× after exposure to 365 nm light. Electron paramagnetic resonance measurements confirm the formation of lophyl radicals within irradiated o‐Cl‐HABI samples that persist with a lifetime of 1.8 h. These radicals are hypothesized to facilitate intermediate steps during the combustion process. Spatially localized irradiation of a NC strip results in selectively enhanced burn velocity in the photoconverted region. Photochemically triggered radical formation introduces an innovative approach to modulate the combustion rate, potentially enabling on‐demand propulsion control in aerospace and defense applications.