液滴在超疏水植物叶面的沉积:实验和分子动力学模拟

Experimental and Molecular Dynamic Simulation of Droplet Deposition on Superhydrophobic Plant Leaf Surfaces

农药液滴在靶标植物叶面的动态沉积对于提高农药利用率具有重要的意义,特别是在超疏水植物叶面的动态沉积。在本文中,我们利用生物基表面活性剂和甘油之间的氢键作用来增强液滴在超疏水植物叶面的有效沉积。在较低浓度的山梨醇-烷基胺表面活性剂溶液中,添加0.001%的甘油,可有效抑制液滴在不同超疏水/疏水植物叶片表面的弹跳和飞溅行为。结果表明,甘油的加入并没有显著改变山梨醇-烷基胺表面活性剂溶液的表面张力、粘度和聚集体的形态。核磁共振波谱(DOSY)显示,甘油加速了山梨醇-烷基胺表面活性剂分子的扩散速度。利用分子动力学模拟,对山梨醇-烷基胺表面活性剂/甘油体系的能量演化及表面活性剂相对于固体表面距离的分布进行了研究。这项目工作不仅为抑制液滴在植物叶面的弹跳飞溅提供了一种建设性的方法,而且为选择农用表面活性剂提供了理论基础。

Pesticide droplet deposition on targeted plant leaf surfaces is of great importance but remains a significant challenge, especially on leaf surfaces of superhydrophobic plants. The loss of sprayed pesticide droplets leads to the overuse of pesticides and environmental pollution. Therefore, in this study, we aimed at developing a system that was capable of enhancing droplet deposition on the surfaces of superhydrophobic plant leaves via hydrogen bonding between a biobased surfactant and glycerol at low concentration(0.25%). The system based on the sorbitol-alkylamine surfactant(denoted as SSAS-C12) with a small amount of glycerol(0.001%) could efficiently inhibit droplet bouncing and splashing on different superhydrophobic/hydrophobic plant leaf surfaces. The results obtained indicated that the addition of glycerol did not change the surface tension, viscosity, contact angles on the plant leaf surfaces, and aggregate morphology of the SSAS-C12solutions. Diffusion-ordered nuclear magnetic resonance spectroscopy revealed that glycerol accelerated the diffusion of SSAS-C12molecules. More specifically, SSAS-C12molecules could diffuse and adsorb on plant leaf surfaces within a short period of time. Other surfactants(denoted as DSSAS-C12and BAPO-C12) with varying numbers of hydroxyl groups were used to verify the enhancement of the deposition on superhydrophobic plant leaf surfaces caused by hydrogen bonding. It was revealed that a decrease in the number of hydroxyl groups in the surfactant molecules led to a decrease in the number of hydrogen bonds between the glycerol and surfactant molecules. Moreover, the diffusion rates of the DSSAS-C12and BAPO-C12molecules in solution were low, causing the surfactant molecules to not reach the solid-liquid interface in time. Consequently, the droplets containing surfactant molecules(of DSSAS-C12or BAPO-C12) bounced and broke up on the surfaces of plant leaves. Finally, we used molecular dynamics(MD) simulations to explore the energy and molecular distribution of different surfactant-glycerol mixtures. The energy evolution of the SSAS-C12-glycerol system and the distribution of surfactant molecules relative to the distance from the solid surface in the MD simulations showed that the addition of glycerol twisted the headgroup in SSAS-C12via hydrogen bonding with glycerol. In this case, SSAS-C12molecules experienced rapid diffusion and adsorption on the solid interface. Therefore, this study not only provided a constructive way to overcome the bouncing behavior of droplets but also prompted us to verify whether all hydrogen bonding interactions among different molecules could display similar control efficiencies through the rational selection of additives.