Hu Xuzhi, Gong Haoning, Liu Huayang, Wang Xi, Wang Weimiao, Liao Mingrui, Li Zongyi, Ma Kun, Li Peixun, Rogers Sarah, Schweins Ralf, Liu Xuqing, Padia Faheem, Bell Gordon, Lu Jian R
Biological Physics Group, Department of Physics and Astronomy, School of Natural Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
Department of Materials, School of Natural Sciences, the University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
J Colloid Interface Sci. 2022 Jul 15;618:78-87. doi: 10.1016/j.jcis.2022.03.002. Epub 2022 Mar 4.
Nonionic alkyl ethoxylate surfactants are widely used in agrochemicals to facilitate the permeation of systemic herbicides and fungicides across the plant waxy film. Industrial grade surfactants are often highly mixed and how the mixing affects their interactions with pesticides and wax films remains largely unexplored. A better understanding could enable design of mixed nonionic surfactants for herbicides and fungicides to maximize their efficiency and reduce wastage whilst controlling their impact on plant wax films.
In this study, nonionic surfactants with general structure n-oxyethylene glycol monododecyl ether (CE) were used to form surfactant mixtures with the same average ethoxylate numbers but different hydrophilic-lipophilic balance (HLB) values. Their mixed micellar systems were then used to solubilize a herbicide diuron (DN) and a fungicide cyprodinil (CP), followed by plant wax solubilization upon contact with wax films. These processes were monitored by H NMR and SANS.
Pesticide solubilization made surfactant micelles effectively more hydrophobic but subsequent wax dissolution caused pesticide release and the restoration of the micellar amphiphilicity. Nonionic surfactants with lower HLBs form larger nanoaggregates, show enhanced wettability, and have better ability to solubilize and permeate pesticides across the wax film, but may cause significant damage to plant growth. These observations help explain why herbicides applied on weeds would benefit from surfactants with lower HLB values while fungicides require surfactants with HLBs to balance between delivery efficiency and potential phytotoxicity risks.
非离子烷基乙氧基化物表面活性剂广泛用于农用化学品中，以促进内吸性除草剂和杀菌剂透过植物蜡质膜。工业级表面活性剂通常高度混合，而这种混合如何影响它们与农药和蜡膜的相互作用在很大程度上仍未得到探索。更好地理解这一点可以设计用于除草剂和杀菌剂的混合非离子表面活性剂，以最大限度地提高其效率并减少浪费，同时控制它们对植物蜡膜的影响。
在本研究中，具有通式n-氧乙烯二醇单十二烷基醚（CE）的非离子表面活性剂用于形成具有相同平均乙氧基化数但不同亲水亲油平衡（HLB）值的表面活性剂混合物。然后用它们的混合胶束体系增溶除草剂敌草隆（DN）和杀菌剂嘧菌环胺（CP），随后与蜡膜接触时增溶植物蜡。这些过程通过核磁共振氢谱（H NMR）和小角中子散射（SANS）进行监测。
农药增溶使表面活性剂胶束有效地变得更疏水，但随后的蜡溶解导致农药释放并恢复胶束的两亲性。具有较低HLB值的非离子表面活性剂形成更大的纳米聚集体，表现出增强的润湿性，并且具有更好的增溶和使农药透过蜡膜的能力，但可能对植物生长造成显著损害。这些观察结果有助于解释为什么施用于杂草的除草剂会受益于具有较低HLB值的表面活性剂，而杀菌剂则需要具有HLB值的表面活性剂来平衡递送效率和潜在的植物毒性风险。
