Figure 2
Transport of AuNPs by the convective internal flow in a sessile drop. (a) Schematics showing the dynamic behaviors of AuNPs moving toward the contact lines (CL) of a drop on the leaf surface by evaporation-driven internal flow. At the initial time (t = ti), AuNPs are uniformly distributed in the sessile drop. As the drop evaporates, AuNPs are translocated to the regions near the leaf surface. (b,c) Dynamical variations in AuNPs when a drop evaporates on a glass substrate. (b) Gray level fluctuations indicating the light intensity profile show the position of AuNP clusters along a yellow line. Inset is a contrast-enhanced X-ray image showing the side view of the drop. (c) Temporal variation in the height of AuNP clusters (hAuNPs). The gradual decrease in hAuNPs shows the transport of AuNPs toward the glass surface. (d) Sequential X-ray images show the top view of AuNP clusters gathering toward the CL region due to evaporation-driven internal flow. Accordingly, stomata positioned near the CL are easily infiltrated by wicking of AuNP suspension. Magnified images in blue box show temporal variations in the position of AuNP clusters. (e) Velocity field of the flow in the sessile drop deposited on a glass substrate, measured by applying a PIV technique from the top view. (f,g) Temporal variations in contact angle (CA) of a sessile drop on (f) a flat glass substrate and (g) the abaxial surface of P. frutescens (n = 1). Insets show the side view of a 2 μl sessile drop and \(\theta\) indicates CA.
