Effect of Wetting on Drop Splashing of Newtonian Fluids and Blood

Abstract

We investigate the impact velocity beyond which the ejection of smaller droplets from the main droplet (splashing) occurs for droplets of different liquids impacting different smooth surfaces. We examine its dependence on the surface wetting properties and droplet surface tension. We show that the splashing velocity is independent of the wetting properties of the surface but increases roughly linearly with increasing surface tension of the liquid. A preexisting splashing model and simplification are considered that predict the splashing velocity by incorporating the air viscosity. Both the splashing model and simplification give a good prediction of the splashing velocity for each surface and liquid, demonstrating the robustness of the splashing model. We also show that the splashing model can also predict the splashing velocity of blood, a shear-thinning fluid.

Role of the Dynamic Contact Angle on Splashing

“…In agreement with past works, a low contact angle hysteresis is a requirement for superhydrophobic substrates [26,37]. Our experiments (example in the Supplemental Material [34]) and those by Goede et al [21], confirm the lifting of the lamella and splashing near the critical impact velocity, occur in the range of 0.4 to 1.2 ms after impact. Consequently, we expect wettability and, hence, the contact angle to play an important role in this timescale (hundreds of microseconds).…”

“…Further studies have analyzed the role of the ambient gas on the lubrication force lifting the lamella [7,10,20,21] concluding that the surrounding gas viscosity is, arguably, the most influential parameter on splashing. Surprisingly, air at the impact point plays no significant role on splashing, but it is the air at the spreading edge that influences it [8,22,23].…”

Droplet Splashing on an Inclined Surface

“…Recent studies [18,[25][26][27][28][29][30][31] do not provide confirmation about the potential formation of an air film underneath the lamella tip before the splash initiation. A model based on the lamella aerodynamics [20] appears to be suitable for applications to a variety of conditions [20][21][22][32][33][34][35] and will be used in the present study. The majority of the existing studies are focused on the orthogonal impact while most impacts occurring in nature and in applications are oblique to the surface [1].…”

Hidden prompt splashing by corona splashing at drop impact on a smooth dry surface

“…At atmospheric conditions, the threshold velocity V c for surrounding-gas-dependent splashing for small Oh drops has been proposed V c = 0.080 34 σ 4/5 μ −3/5 g (ρD) −1/5 [37], by approximating the criterion proposed by Riboux and Gordillo [38]. Given that surrounding-gas-dependent splashing is classified as corona splashing [14], the criterion for corona splashing for small Oh drops at atmospheric conditions can be written as Oh Re 5/8 = K c , where K c = 0.207(μ/μ g ) 3/8 .…”

“…Note that Eq. 3is valid only for Re 1/6 Oh 2/3 < 0.223 [37,40], i.e., Oh < 0.0248. The results of the experiments that can support the validity of Eq.…”