Asymmetric Spreading of a Drop upon Impact onto a Surface

Abstract

Study of the spreading of an impacting drop onto a surface has gained importance recently due to applications in printing, coating, and icing. Limited studies are conducted to understand asymmetric spreading of a drop seen upon drop impact onto a moving surface; there is no relation to describe such spreading. Here, we experimentally studied the spreading of a drop over a moving surface; such study also provides insights for systems where a drop impacts at an angle relative to a surface, i.e., drop has both normal and tangential velocities relative to the surface. We developed a model that for the first time allows prediction of time evolution for the asymmetric shape of the lamella during spreading. The developed model is demonstrated to be valid for a range of liquids and surface wettabilities as well as drop and surface velocities, making this study a comprehensive examination of the topic. We also found out how surface wettability can affect the recoil of the drop after spreading and explained the role of contact angle hysteresis and receding contact angle in delaying the recoil process.

Nonwet Kingfisher Flying in the Rain: The Tumble of Droplets on Moving Oriented Anisotropic Superhydrophobic Substrates

“…However, the modification of the wetting dynamics by movement is reflected in the higher Weber number regime (We = 25.6). It can also be observed that the spreading and receding phases of the lamella were thinner downstream at a given time (see the right side of the dotted lines in Figure 3b and 3c), which corresponds reasonably well with the findings of previous studies 22,24 . No distinguishable morphology of the droplets was observed during the spreading phase within 3.00 ms, as illustrated in Figure 3a, and once the droplets began to spread in the direction of the texture and downstream (t = 3.08 ms, Figure 3b), their centers of gravity began to change transiently with the direction of motion.…”

How Wettability Controls Nanoprinting

“…Due to the huge number of applications involved, drop impact has been intensively studied in the past years as, for example, the modeling of the influence of the drop size on the time evolution of the dynamic contact angle and contact radii [6], the study of the transition between bounce/stick/splash of nanodroplets [7,8], the impact of nanodroplets on textured surfaces [9], droplet impact over inclined substrates studied experimentally [10] or by using molecular dynamics techniques [11], experimen-tal studies of drop impact over a moving substrate [12], etc. 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.…”

Effect of thermo‐oxidative aging on surface characteristics of benzoxazine and epoxy copolymer

“…The balance between the kinetic energy, capillary, and viscous forces ends the spreading process and the lamella eventually reaches a maximum wetting length, L w , at time, t max 23–25 ; afterwards the droplet recedes back toward the center of the impact point. The impact dynamics hence is defined by the interaction of this lamella with the surface and the surrounding gas, 26 which makes the surface properties to play an important role in controlling the impact dynamics 27,28 . Usually droplet impact physics is observed over laboratorial tests performed on stationary solid surfaces.…”