Synthesis and interfacial properties of N-propyl double-chain sodium carboxylate adjuvants at various pH values

Low pesticide utilization efficiency represents a major constraint on the green and sustainable development of agriculture. It also directly affects agricultural ecological security and resource use efficiency. Pesticide adjuvants, as essential components throughout the entire pesticide application, play a key role in controlling spray dispersion, spreading, adhesion and retention. Therefore, they are crucial for ensuring accurate pesticide dose delivery and enhancing effective utilization. In practice, pesticide application environments are highly complex, characterized by factors such as pH fluctuations, variable temperature and humidity. These factors impose strict requirements on the interfacial adaptability of adjuvants in complex environments. Surfactants containing acid-base sensitive groups, which can regulate interfacial properties under external conditions, have been studied in other fields but not yet systematically applied in the field of pesticides. In this work, five N-propyl double-chain sodium carboxylate surfactants with different carbon chain lengths (C₇-C₁₁) were designed and synthesized, using amino and carboxyl groups as pH-sensitive functional groups. which alter the molecular charge state under varying pH conditions, thereby regulating the interfacial properties of liquid droplets. The effects of carbon chain length and pH on surface activity, wetting behavior, and adhesion performance were investigated. Meanwhile, we clarified the response mechanisms underlying the key interfacial processes in pesticide delivery. The results indicate that these adjuvants exhibit superior wetting and adhesion performance under acidic conditions. Moreover, surfactants with longer carbon chains possess higher work of adhesion. Notably, compound C₁₁ exhibited a contact angle of 59.1° on rapeseed leaf surfaces at pH 2, which was significantly lower than 72.8° measured at pH 10. These properties help pesticides wet and attach to acidic disease sites, indicating the potential of the synthesized compounds as surface-active adjuvants. This study introduces pH-responsive surfactants containing acid-base sensitive groups into pesticide adjuvant systems, providing a theoretical reference for developing pesticide adjuvants with environmental adaptability. It is also of significance for improving pesticide utilization efficiency.