Acta Phys. -Chim. Sin. ›› 2022, Vol. 38 ›› Issue (12): 2207006.doi: 10.3866/PKU.WHXB202207006

Special Issue: Special Issue in Honor of the 120’s Anniversary of Academician Ying Fu

• ARTICLE • Previous Articles     Next Articles

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

Chong Cao1, Pei Zhang2,*(), Lidong Cao1, Mingxin Liu1, Yuying Song1, Peng Chen2, Qiliang Huang1,*(), Buxing Han2,*()   

  1. 1 Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
    2 Key Laboratory of Colloid and Interface and Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
  • Received:2022-07-05 Accepted:2022-08-02 Published:2022-08-12
  • Contact: Pei Zhang,Qiliang Huang,Buxing Han E-mail:zhangpei@iccas.ac.cn;qlhuang@ippcaas.cn;hanbx@iccas.ac.cn
  • About author:Buxing Han, Email: hanbx@iccas.ac.cn (B.H.)
    Pei Zhang, Email: zhangpei@iccas.ac.cn (P.Z.)
    Qiliang Huang, Email: qlhuang@ippcaas.cn (Q.H.)
  • Supported by:
    the National Natural Science Foundation of China(32072469);the National Natural Science Foundation of China(22073104);the Central Public-interest Scientific Institution Basal Research Fund(S2022XM16)

Abstract:

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 bio-based 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-C12 solutions. Diffusion-ordered nuclear magnetic resonance spectroscopy revealed that glycerol accelerated the diffusion of SSAS-C12 molecules. More specifically, SSAS-C12 molecules could diffuse and adsorb on plant leaf surfaces within a short period of time. Other surfactants (denoted as DSSAS-C12 and 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-C12 and BAPO-C12 molecules 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-C12 or 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-C12 via hydrogen bonding with glycerol. In this case, SSAS-C12 molecules 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.

Key words: Impact dynamics, Bio-based surfactant, Glycerol, Hydrogen bond, Molecular dynamic simulation

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