Abstract:

Surfactants play important roles in agricultural production by reducing surface tension, promoting liquid penetration, and enhancing adsorption, thereby improving the efficiency of pesticide utilization. A series of quaternary ammonium cationic surfactants NDA-C5 to NDA-C8 were prepared by using N, N-dimethyldecylamine and fatty acids as raw materials through quaternization reaction and ion exchange reaction. The structures were characterized by FT-IR, ¹H NMR and ¹³C NMR. The wetting and penetration, spreading, static surface tension, and dynamic surface tension were studied. The results showed that among the series of products, NDA-C8 exhibited the best performance. When the mass fraction of NDA-C8 was 0.100% （w/%）, the static surface tension was reduced to 25.9 mN/m, the wetting time was 260 s, and the spreading area on superhydrophobic organic glass reached 102 mm^2.In addition, NDA-C8 demonstrated excellent dynamic surface tension performance, with the surface tension rapidly decreasing from 53.3 mN/m to 34.2 mN/m in the range of 0.01 s to 1 s. The quaternary ammonium cation had good interfacial activity, and the adsorption diffusion coefficient at the interface further increased with the increase of the carbon chain length of counterion, so that the surface active properties were improved. In contrast to static surface tension, dynamic surface tension could more accurately reflect the situation in actual use. Furthermore, the preparation process of this series of products was simple, and the cost of raw materials was low, so they had promising application prospects.

Key words: cationic surfactant, quaternization, ion-exchange, surface activity