Surfactant-induced enhancement of droplet adhesion in superhydrophobic soybean (Glycine max L.) leaves

Abstract

This study performed with soybean (Glycine max L.), one of the most important crops for human and animal nutrition, demonstrates that changes in the leaf surface structure can increase the adhesion of applied droplets, even on superhydrophobic leaves, to reduce undesirable soil contamination by roll-off of agrochemical formulations from the plant surfaces. The wettability and morphology of soybean (Glycine max L.) leaf surfaces before and after treatment with six different surfactants (Agnique® SBO10 and five variations of nonionic surfactants) have been investigated. The leaf surface structures show a hierarchical organization, built up by convex epidermal cells (microstructure) and superimposed epicuticular platelet-shaped wax crystals (micro- to nanostructure). Chemical analysis of the epicuticular wax showed that 1-triacontanol (C30H61OH) is the main wax component of the soybean leaf surfaces. A water contact angle (CA) of 162.4° (σ = 3.6°) and tilting angle (TA) of 20.9° (σ = 10.0°) were found. Adherence of pure water droplets on the superhydrophobic leaves is supported by the hydrophilic hairs on the leaves. Agnique® SBO10 and the nonionic surfactant XP ED 75 increased the droplet adhesion and caused an increase of the TA from 20.9° to 85° and 90°, respectively. Scanning electron microscopy showed that surfactants with a hydrophilic–lipophilic balance value below 10 caused a size reduction of the epicuticular wax structures and a change from Cassie–Baxter wetting to an intermediate wetting regime with an increase of droplet adhesion.

Attachment ability of the polyphagous bug Nezara viridula (Heteroptera: Pentatomidae) to different host plant surfaces

“…These microscopic (length: 1.12 ± 0.25 μm, N = 30; width: 0.51 ± 0.09 μm, N = 20) flat wax projections with irregular margin protrude more or less perpendicularly from the surface. Contrary to previous authors indicating either asterisk wax projections 23 or rosettes composed of five to ten platelets 24 , we detected rather low degree of aggregation of irregular wax platelets. Stomata occurring on both leaf sides (density on the abaxial side is about 80 mm −2 ) are poorly visible on the adaxial surface.…”

Water Repellency and Hydrophobicity of Some Major Agricultural Crop Residues

“…All three oilseed species had similar hydrophobicity (0.7; Table 2). Green soybean leaves are considered super‐hydrophobic with contact angles of 162° because of surface sculptures built up by convex hexagonal cells and superimposed epicuticular wax crystals with its hydrophobic surface chemistry (Hagedorn et al, 2017). In addition, soybean leaves also have long (2‐mm) trichomes or hairs on both sides of the leaves which may contribute to water repellency.…”

Effect of Oxygen Plasma on Sprout and Root Growth, Surface Morphology and Yield of Garlic

“…Particularly, structures in the size range of a few hundred nm are typically hydrophobic, imparting water repellent properties on plant surfaces that are covered with such crystals. For example, surface wetting and droplet adhesion of soybean leaves increased after wax platelets were dissolved with surfactants [48]. Further, size and quantity of wax crystals are significantly more important for water affinity than wax chemistry [48], so it is reasonable to assume that the minimal surface oxidation that we observe on cloves is less significant than the extensive crystal formation.…”