Nanodroplets Impact on Rough Surfaces: A Simulation and Theoretical Study

Abstract

Impact of droplets is widespread in life, and modulating the dynamics of impinging droplets is a significant problem in production. However, on textured surfaces, the micromorphologic change and mechanism of impinging nanodroplets are not well-understood; furthermore, the accuracy of the theoretical model for nanodroplets needs to be improved. Here, considering the great challenge of conducting experiments on nanodroplets, a molecular dynamics simulation is performed to visualize the impact process of nanodroplets on nanopillar surfaces. Compared with macroscale droplets, apart from the similar relation of restitution coefficient with the Weber number, we found some distinctive results: the maximum spreading time is described as a power law of impact velocity, and the relation of maximum spreading factor with impact velocity or the Reynolds number is exponential. Moreover, the roughness of substrates plays a prominent role in the dynamics of impact nanodroplets, and on surfaces with lower solid fraction, the lower attraction force induces an easier rebound of impact nanodroplets. At last, on the basis of the energy balance, through modifying the estimation of viscous dissipation and surface energy terms, we proposed an improved model for the maximum spreading factor, which shows greater accuracy for nanodroplets, especially in the low-to-moderate velocity range. The outcome of this study demonstrates that a distinctive dynamical behavior of impinging nanodroplets, the fundamental insight, and more accurate prediction are very useful in the improvement of the hydrodynamic behavior of the nanodroplets.

Nanodroplets of Polymer Solutions on Solid Surfaces: Equilibrium Structures and Solvent Evaporation

“…The vast majority of computer simulations of the aforementioned systems deal with molecular dynamics, − and some employ the method of Monte Carlo. , Most of the tasks studied can be divided into two classes: simulations of droplets of “pure” (one-component) liquids − ,,, and those formed by multicomponent liquids. ,,, For the pure liquids, the studies mainly dealt with evaporation of the droplets under different conditions. It is also worth mentioning simulations of droplets’ motion ,,, because physical processes in the droplets caused by their motion are difficult to register in experiments. For example, Gao et al demonstrated that nanodroplets could bounce when they collide with textured surfaces or when two nanodroplets coalesce on the textured surfaces. , The field of the multicomponent droplets is much less developed.…”

“…It is also worth mentioning simulations of droplets’ motion ,,, because physical processes in the droplets caused by their motion are difficult to register in experiments. For example, Gao et al demonstrated that nanodroplets could bounce when they collide with textured surfaces or when two nanodroplets coalesce on the textured surfaces. , The field of the multicomponent droplets is much less developed. In particular, there are no computer simulations of nanodroplets of polymer solutions and structures formed after solvent evaporation.…”

“…24−27 The vast majority of computer simulations of the aforementioned systems deal with molecular dynamics, 28−39 and some employ the method of Monte Carlo. 40,41 Most of the tasks studied can be divided into two classes: simulations of droplets of "pure" (one-component) liquids [30][31][32][33][34][35][36]38,39,41 and those formed by multicomponent liquids. 28,29,37,40 For the pure liquids, the studies mainly dealt with evaporation of the droplets under different conditions.…”

Nanodroplets impact on surfaces decorated with ridges

“…For instance, Koplik et al [14] employed MD to study the impact of nanodroplets of Lennard-Jones liquids, and observed various phenomena including stick, bounce, splash, and disintegrate, depending on the initial velocity and composition of droplets. Koishi et al [29] and Gao et al [30] used MD to study the bouncing performance of nanodroplets on columnar array structures, with a focus to develop the theories and models on the spreading dynamics and energy transformation, without the consideration of the contact time. Li et al [31] investigated the effect of nanoridges on reducing liquid-solid contact time.…”

Spreading of a droplet impacting on a smooth flat surface: how liquid viscosity influences the maximum spreading time and spreading ratio

“…Hence, its modeling for the viscous dissipation characterization becomes particular of concern to many studies. 21,22,36,38,39 The main models based on the energy balance approach are summarized in the second part of We…”