Synthesis of a photoresponsive cationic surfactant PCDA-C₆-NH₃⁺ and its regulation of droplet evaporation

Droplets evaporation on plant leaves plays an important role in the utilization of pesticides. Although traditional surfactants can change the evaporation mode or evaporation rate of droplets, they cannot adjust the evaporation process effectively according to external stimuli. In this research, a photo-responsive diacetylene-based cationic surfactant (PCDA-C₆-NH₃⁺) was designed and synthesized, where 10,12-pentacosadiynoic acid and protonated terminal amine were used as the photo-responsive motiey and the hydrophilic cation, respectively. The UV light-induced topochemical polymerization of PCDA-C₆-NH₃⁺ was studied by UV-Vis spectroscopy. Its surface activity and evaporation behavior before and after UV irradiation were analyzed by static surface tension and dynamic contact angle. The results showed that the aggregation state of PCDA-C₆-NH₃⁺ can be regulated by UV light during the droplets evaporation process, because of its topochemical polymerization. This work has provided a new strategy to adjust the evaporation of droplets, which is of great significance for improving the utilization rate of pesticides.