Impact Dynamics of Nanodroplets on V-Shaped Substrates: Asymmetrical Behavior and Fast-Rebound Dynamics

Abstract

Controlling the drop impact behaviors plays an important role in both designing surface functional materials and improving industrial techniques. Here, the impact dynamics of nanodroplets on “V-shaped” substrates is studied, which is manifested as asymmetrical spreading and retraction behaviors that could be weakened by increasing the angles of the “V” shape, accompanied by the evolution of the shape from leaf-like, stripe-like, to dumbbell-like at v = 20 Å/ps. When v increases to 40 Å/ps, the previously deposited nanodroplets could be transformed to a rebound one at α = 60 and 90°, which is ascribed to the combined effect of the confinement conditions and the extrusion force. Furthermore, an impact behavior map as a function of impact velocity and angle is depicted, which suggests that a decrease in angles or an increase in the impact velocity is likely to cause the nanodroplets to rebound. More importantly, the results give visible evidence that compared to the flat substrates, the V-shaped structure is advantageous for achieving a fast-rebound behavior even at a low speed of impact, which should be good news for practical applications in many multidisciplinary fields, such as self-cleaning, anti-icing/fogging, pollution prevention, energy storage, and so forth.

Simulation of droplet impact dynamics on V-shaped walls

“…Their results showed that when the angle of the inclined surface was small, the droplets formed long tails, while the angle of the inclined surface was large, the droplets had shapes closer to teardrops. For a V-shaped wall (namely inclined walls with confined space), to the best knowledge of the present authors, there are only two publications by Agrawal et al (Agrawal, Khurana, & Dhar, 2021) and Li et al (T. Li & Wu, 2021). Agrawal et al (Agrawal et al, 2021) studied experimentally the collisions of droplets against V-shaped valleys.…”

“…However, the effect of eccentricity ratio was not considered in their work. Li et al (T. Li & Wu, 2021) investigated droplets impacting V-shaped substrates using molecular dynamics. In their work, two collisions were observed: rebound and deposition.…”

Coalescence-Induced Jumping for Removing the Deposited Heterogeneous Droplets: A Molecular Dynamics Simulation Study

“…Recently, an asymmetric V-groove was designed on the superhydrophobic surfaces for achieving more than 700% increase in energy conversion efficiency, which not only effectively enhances the velocity of coalescence-induced droplet jumping, but also randomly changes the jumping direction by controlling the groove angle . Additionally, some experimental studies also reported many well-designed structures that are useful to promote the self-propelled jumping behaviors of the coalesced droplet, such as the nanograss zigzag structures, hierarchical microcone structures, , and V-shaped grooves. , …”

“…22 Additionally, some experimental studies also reported many well-designed structures that are useful to promote the self-propelled jumping behaviors of the coalesced droplet, such as the nanograss zigzag structures, 23 hierarchical microcone structures, 24,25 and V-shaped grooves. 26,27 In addition to the surface structures, the droplet itself also plays a critical role in the coalescence-induced jumping behaviors. One concern first raised is the size effect.…”

Molecular Dynamics Simulation of Nanodroplets Impacting Stripe-Textured Surfaces

“…Gao et al investigated the phenomenon of droplet impinging on the surface of nanopillars under microscopic conditions and introduced the parameter of solid fraction (representing surface roughness) to modify the maximum spreading factor model. Liu et al and Li et al analyzed the dynamic behavior of nanodroplets impinging on a single ridge and a single-groove structure, respectively. Both structures can significantly reduce the contact time of the droplets.…”