On the analysis of the contact angle for impacting droplets using a polynomial fitting approach

Abstract

Practical considerations on the measurement of the dynamic contact angle and the spreading diameter of impacting droplets are discussed in this paper. The contact angle of a liquid is commonly obtained either by a polynomial or a linear fitting to the droplet profile around the triple-phase point. Previous works have focused on quasi-static or sessile droplets, or in cases where inertia does not play a major role on the contact angle dynamics. Here, we study the effect of droplet shape, the order of the fitting polynomial and the fitting domain, on the measurement of the contact angle on various stages following droplet impact where the contact line is moving. Our results, presented in terms of the optical resolution and the droplet size, show that a quadratic fitting provides the most consistent results for a range of various droplet shapes. As expected, our results show that contact angle values are less sensitive to the fitting conditions for the cases where the droplet can be approximated to a spherical cap. Our experimental conditions include impact events with liquid droplets of different sizes and viscosities on various substrates. In addition, validating past works, our results show that the maximum spreading diameter can be parameterised by the Weber number and the rapidly advancing contact angle.

Resin Wettability Correlates Linearly to Interfacial Fracture Energy between Thermosetting Elastomers and Glass

“…32 Quetzeri-Santiago et al also discussed the impact of liquid viscosity on the contact angles using three types of substrates and liquids including pure water and water−glycerol solutions and found that the larger the liquid viscosity is, the larger are the contact angles. 45 Since liquid viscosity originates from the attractive/cohesive forces between liquid molecules, a higher resin viscosity tends to prevent the relative motion of molecules. This difference in viscosity would further affect the viscous force when different resin systems flow on the glass surfaces, leading to lower contact angles for lower-viscosity systems, assuming that surface energies are equal.…”

Controlling droplet splashing and bouncing by dielectrowetting

“…Image analysis was performed on spreading experiments to extract dynamic contact angles , spreading diameters, impact speeds and droplet sizes by a custom MATLAB code. Details of this Matlab algorithm are found elsewhere 45 .…”

UAV spraying on citrus crop: impact of tank-mix adjuvant on the contact angle and droplet distribution

“…The research perspectives of the studies related to UAV spraying mentioned above are mainly from the angles of sprayers and spraying technologies, while the influences of spraying liquid property on droplet distribution are rarely noticed. Contact angle (CA), which quantifies the wettability of a solid surface by a liquid, is the geometric angle made between a solid/liquid/gas interface on a surface, and it is an important metric for evaluating the likeness of a liquid on wetting the solid surface ( Dwivedi et al, 2017 ; Gribanova, Kuchek & Larionov, 2016 ; Quetzeri-Santiago, Castrejón-Pita & Castrejón, 2020 ). Low CA values indicate that the liquid could spread and adhere to the solid surface easily, whereas large CA values indicate the difficulty of a liquid to wet the solid surface due to repelling of solid surface to water ( Huhtamki et al, 2018 ).…”