Estimation of viscous dissipation in nanodroplet impact and spreading

Abstract

The developments in nanocoating and nanospray technology have resulted in the increasing importance of the impact of micro-/nanoscale liquid droplets on solid surface. In this paper, the impact of a nanodroplet on a flat solid surface is examined using molecular dynamics simulations. The impact velocity ranges from 58 m/s to 1044 m/s, in accordance with the Weber number ranging from 0.62 to 200.02 and the Reynolds number ranging from 0.89 to 16.14. The obtained maximum spreading factors are compared with previous models in the literature. The predicted results from the previous models largely deviate from our simulation results, with mean relative errors up to 58.12%. The estimated viscous dissipation is refined to present a modified theoretical model, which reduces the mean relative error to 15.12% in predicting the maximum spreading factor for cases of nanodroplet impact. C 2015 AIP Publishing LLC. [http://dx.

Early stage of nanodroplet impact on solid wall

“…Such a rebound process for the small value of ϵ * was also observed in the previous MD simulations. 10,14 Next, we investigate the spreading diameter of the molecular layers (Layers 1-4 shown in Fig. 4) using the control volumes as shown in Fig.…”

“…Electronic mail: kobakazu@eng.hokudai.ac.jp Taking advantage of the ease of treating the liquid-wall interaction, several studies of nanodroplet impact were conducted using molecular dynamics (MD) simulation. [6][7][8][9][10][11][12][13][14] Recently, Koplik and Zhang 12 investigated the behaviors of nanodroplets consisting of short chains of Lennard-Jones liquids after impact with the solid surface, and Zhang et al 13 studied the influence of wettability and roughness of solid surfaces for nanodroplet impact. From these studies, detailed spreading dynamics due to the nanodroplet impact have been clarified.…”

How Wettability Controls Nanoprinting

“…Given the strong deformation of the droplet during impact, especially for cases with relatively high impact velocities, the evaluation of the dynamic contact angle is not very accurate in comparison with the measurement of the contact diameter of the drop. Furthermore, different models have been proposed to characterize the maximum spreading diameter of a drop at macroscale [13][14][15][16][17][18]. Most of these models are either empirical or based on energy balance plus viscous dissipation but not all take into account the wetting properties between the liquid and the solid phases [14,16,18].…”

“…Furthermore, different models have been proposed to characterize the maximum spreading diameter of a drop at macroscale [13][14][15][16][17][18]. Most of these models are either empirical or based on energy balance plus viscous dissipation but not all take into account the wetting properties between the liquid and the solid phases [14,16,18]. Moreover, these models have been compared with experiments at a macroscopic scale but their validity at the nanometric scale, which is essential for many of the applications described above, is still unknown.…”

“…The validity of these approaches is however uncertain at the nanoscale. Based on the analysis of the velocity distribution in MD simulations of water nanodroplets impact, Li et al [18] found that the velocity gradient exist not only in the boundary layer but that it is quite uniform in the droplet. With these considerations, they propose that the viscous dissipation for impact of nanodroplets can be written as…”