Leaf surface structures enable the endemic Namib desert grass
            Stipagrostis sabulicola
            to irrigate itself with fog water

The Namib grass Stipagrostis sabulicola relies, to a large degree, upon fog for its water supply and is able to guide collected water towards the plant base. This directed irrigation of the plant base allows an efficient and rapid uptake of the fog water by the shallow roots. In this contribution, the mechanisms for this directed water flow are analysed. Stipagrostis sabulicola has a highly irregular surface. Advancing contact angle is 98° ± 5° and the receding angle is 56° ± 9°, with a mean of both values of approximately 77°. The surface is thus not hydrophobic, shows a substantial contact angle hysteresis and therefore, allows the development of pinned drops of a substantial size. The key factor for the water conduction is the presence of grooves within the leaf surface that run parallel to the long axis of the plant. These grooves provide a guided downslide of drops that have exceeded the maximum size for attachment. It also leads to a minimum of inefficient drop scattering around the plant. The combination of these surface traits together with the tall and upright stature of S. sabulicola contributes to a highly efficient natural fog-collecting system that enables this species to thrive in a hyperarid environment.

Download Full-text

Quantitative studies on the wetting of leaves by water

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1947.0028 ◽

1947 ◽

Vol 134 (877) ◽

pp. 503-522 ◽

Cited By ~ 65

Keyword(s):

Contact Angle ◽

Water Content ◽

Leaf Surface ◽

Diurnal Fluctuation ◽

Leaf Water Content ◽

Triticum Vulgare ◽

Quantitative Studies ◽

Stomatal Behaviour ◽

Detached Leaves ◽

Advancing Contact Angle

Quantitative studies on the wetting by water of the exterior surfaces of leaves of Sinapis arvensis, Triticum vulgare , and other plants, have been made, using advancing contact angle as a measure of the extent to which wetting takes place. The magnitude of the contact angle of water on a leaf surface has been found to vary regularly with the position of the leaf on the plant and to show also a characteristic diurnal fluctuation through a range which may be as much as 30°. The diurnal variations in contact angle are shown to be correlated with changes in leaf water content. On detached leaves contact angle varies markedly as wilting proceeds, this change being reversible on recovery of turgor. Evidence is presented to show that these variations in the behaviour of water on leaves are caused by changes in the degree of corrugation of the leaf surface produced by changes in the water content of the tissues. The events in the diurnal cycle are explained on this basis. The significance of the observed phenomena in connexion with the retention of water by leaves, the exchange of water and dissolved substances between leaf and water, and stomatal behaviour, is discussed.

Download Full-text

Influence of Multiple Factors on the Wettability and Surface Free Energy of Leaf Surface

Applied Sciences ◽

10.3390/app9030593 ◽

2019 ◽

Vol 9 (3) ◽

pp. 593 ◽

Cited By ~ 4

Author(s):

Yong He ◽

Shupei Xiao ◽

Jianjian Wu ◽

Hui Fang

Keyword(s):

Contact Angle ◽

Free Energy ◽

Surface Free Energy ◽

Solid Surface ◽

Leaf Surface ◽

Plant Protection ◽

Plant Protection Products ◽

Surface Wettability ◽

Multiple Factors ◽

Key Factor

The wettability of plant leaves directly reflects leaf hydrophilicity, which is the key factor that influences the adhesion of liquid pesticide as well as affects plant protection products (PPP) efficacy. Generally, the wettability of leaf surface is quantified by the contact angle and surface free energy (SFE), which are mainly dependent on leaf surface properties, liquid properties and other spraying parameters. Therefore, the aim of this paper was to investigate the SFE of rice and rape leaves with the variation of leaf status, leaf surface, and probe liquid as well as the influence of droplet falling height, solid surface, and PPP concentration on the wettability. The results showed that: (1) the dispersive components of SFE of rice and rape account for a large proportion which are closely related to their hydrophobicity—the abaxial of rape new leaf and the adaxial of rape old leaf are easier to wet comparing with rice and rape leaves in other statuses; (2) the increase of droplet falling height had a significant effect on improving the wettability between wax surface and adjuvant solution, while it had little improving effect on the wettability between wax surface and water; (3) the wettability of different solid surface varied greatly, and the order of wettability from good to bad is water-sensitive paper (WSP), wax, rape leaf, and rice leaf; (4) the effect of PPP concentration on the leaf surface wettability is significant, the contact angle decreased with the increase of PPP concentration, and the wettability of microemulsion is better than that of suspending agent and wettable powder. In conclusion, the SFE and wettability of crop leaf surface determine the suitable type of PPP, studying the influence of multiple factors on leaf surface wettability can provide a reliable reference for providing scientific guidance as well as improving the effective utilization of PPP.

Download Full-text

On the ability of drops to stick to surfaces of solids. Part 3. The influences of the motion of the surrounding fluid on dislodging drops

Journal of Fluid Mechanics ◽

10.1017/s002211208700017x ◽

1987 ◽

Vol 174 ◽

pp. 381-397 ◽

Cited By ~ 68

Author(s):

E. B. Dussan V.

Keyword(s):

Contact Angle ◽

Solid Surface ◽

Specific Problem ◽

Contact Angle Hysteresis ◽

Immiscible Fluid ◽

Planar Surface ◽

Fixed Position ◽

Constant Rate ◽

Advancing Contact Angle ◽

Surrounding Fluid

The ability of a drop to stick to a solid surface is investigated when the surrounding fluid is in motion. The specific problem analysed consists of a small drop on a planar surface immersed in a second immiscible fluid which is flowing parallel to the solid surface at a constant rate of strain. An expression is obtained, in terms of experimentally measurable quantities, for the value of the rate of strain beyond which the drop cannot maintain contact with a fixed position on the solid. The most limiting restrictions assumed in the analysis are that both the advancing contact angle and the contact angle hysteresis must be small.

Download Full-text

Salinity Damage to Norfolk Island Pines Caused by Surfactants. III. Evidence for Stomatal Penetration as the Pathway of Salt Entry to Leaves

Functional Plant Biology ◽

10.1071/pp9780397 ◽

1978 ◽

Vol 5 (3) ◽

pp. 397 ◽

Cited By ~ 19

Author(s):

AM Grieve ◽

MG Pitman

Keyword(s):

Surface Tension ◽

Contact Angle ◽

Leaf Surface ◽

Sea Water ◽

Sea Spray ◽

Water Spray ◽

Araucaria Heterophylla ◽

Norfolk Island ◽

Advancing Contact Angle ◽

Sea Coast

The paper describes the effect of varied surfactant concentrations on penetration of NaCl into leaves of Norfolk Island Pine, Araucaria heterophylla (Salisb.) Franco. It confirms that the damage observed along the sea-coast in Sydney is similar to that produced by high NaCl levels in the foliage. The effect of surfactant in increasing NaCl uptake from sea-water spray is related to the reduction in surface tension and to the advancing contact angle of the spray on the leaf surface. It is suggested that sea-spray enters A. heterophylla needles through the stomata, and that the cuticle is particularly resistant to NaCI, compared with other plant species. Similar penetration and damage was found with sprays of CaCl2, MgCl2 and KCl showing that the damage was not due specifically to NaCI.

Download Full-text

Anisotropic Wetting Characteristics of Biomimetic Rice Leaf Surface with Asymmetric Asperities

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2020.17570 ◽

2020 ◽

Vol 20 (7) ◽

pp. 4331-4335

Author(s):

Mu-Yeon Jang ◽

Jeong-Woo Park ◽

Seung-Yub Baek ◽

Tae-Wan Kim

Keyword(s):

Contact Angle ◽

Leaf Surface ◽

Contact Angle Hysteresis ◽

Dynamic Contact ◽

Contact Angles ◽

Droplet Flow ◽

Biomimetic Surfaces ◽

Rice Leaf ◽

The Difference ◽

Inclined Angle

Rice leaf surface has known as having functional performances such as self cleaning and antifouling as well as directional flowing due to a unique micro structure with groove. In this study, we investigated the effects of asymmetrical cone protrusions on the surface of droplet flow through the contact angle and contact angle hysteresis of the droplet. First, static and dynamic contact angles of droplet on the rice leaf are measured. We found that the rice leaf surface has a directional flow characteristic through the difference of the contact angle hysteresis with flow directions. We also fabricated the rice leaf-like surfaces with asymmetric asperities along microgrooves using rapid prototyping technique and evaluated anisotropic wettability properties for the produced biomimetic surfaces. The experimental results show that the direction of the micro asperity tip relative to the droplet flow and its inclined angle has a very important influence on the anisotropic flow. This research can help to clarify the anisotropic wettability by the surface structure.

Download Full-text