Fig 1.
The surface tension for different concentrations of surfactant solution was measured by the normal Pt-plate (a) and the pendant-drop method (b).
Fig 2.
The typical changes in contact angle and contact diameter of pure water droplets (0%), relatively low concentrations (0.001%, 0.005%), and high concentrations (0.01%, 0.05%).
Furthermore, various evaporation times to achieve the same normalized volume is listed under each image.
Fig 3.
Evolution of the contact angles (blue squares) and contact diameters (red triangles) of a sessile droplet of (a) pure water droplets and (b–f) droplets containing different concentrations of surfactant over the evaporation period on rice leaf surfaces. The distinct evaporation periods (the steady start stage, CCR, and mixed mode) are indicated by vertical dotted lines. The vertical lines are determined by the significant change in the slope of the contact diameter shown by black lines in the picture.
Fig 4.
The scanning electron micrograph of the rice leaf surface used in the experiment.
Fig 5.
Sketches of two main droplet evaporation mode for droplets containing low concentrations of (a, b) 0.001% to 0.005% and high concentrations of (c, d) 0.01% to 0.05%.
Figs (b) and (d) show enlarged sections of (a) and (c), respectively. The color changes are used to represent the evaporation of the droplets. The blue dots respect the vapor evaporated from the droplet surface. Also, the density in Fig (a) with a worse wetting state is higher than that of Fig (c), which has a better wetting state. The higher density of vapor within the small narrow region also restricts the evaporation rate of the droplet.
Fig 6.
Evolution of the ratio of contact angle and contact diameter (contact angle/contact diameter vs. time) for pure water droplets and droplets containing different concentrations of surfactant over the evaporation period.
Fig 7.
(a, b) Evolution of the volume of a pure water droplet and droplets containing different concentrations of surfactant over the whole evaporation time, (v/v0) vs. t and (v/v0)2/3 vs. t, respectively.
Fig 8.
Evolution of the height for water-only droplet and droplets of different concentrations of surfactant with an initial volume of 4 μL on the surface of a rice leaf.
Fig 9.
Average time required to evaporate 90% of the volume of a pure water droplet and those containing different concentrations of adjuvant (initial volume ≈ 4 μL) on natural rice leaf surfaces.
Fig 10.
The dimensionless droplet mass plotted against the dimensionless time (a). The rate of mass loss of the droplet vs the contact angle (b). The color lines represent the experimental data, which are derived from the measured droplet volume. The black solid lines represent the theoretical prediction according to Popov’s model. The experimental data are scaled according to (6). The time is set to 0 at the end of the droplet life.