Dissipation of oscillatory contact lines using resonant mode scanning

Abstract

Moving contact-lines (CLs) dissipate. Sessile droplets, mechanically driven into resonance by plane-normal forcing of the contacting substrate, can exhibit oscillatory CL motions with CL losses dominating bulk dissipation. Conventional practice measures CL dissipation based on the rate of mechanical work of the unbalanced Young's force at the CL. Typical approaches require measurements local to the CL and assumptions about the "equilibrium" contact angle (CA). This paper demonstrates how to use scanning of forcing frequency to characterize CL dissipation without any dependence on measurements from the vicinity of the CL. The results are of immediate relevance to an International Space Station (ISS) experiment and of longer-term relevance to Earthbased wettability applications. Experiments reported here use various concentrations of a water-glycerol mixture on a lowhysteresis non-wetting substrate.

Drop impact on solids: contact-angle hysteresis filters impact energy into modal vibrations

“…Time proceeds clockwise. The dissipation during one cycle of CL motion is proportional to the area inside the rectangle, (Xia & Steen 2020). ( a ) Laboratory generated results for 30 oscillations of a sessile drop on P0 driven at an acceleration, .…”

“…For near neutral wetting systems, and , Xia & Steen (2020) showed that the damping ratio of the harmonically driven drop is a measure of dissipation within the drop, and that the Young's force, (3.1), can be expanded in Taylor series resulting in the damping ratio being proportional to the area of the region enclosed in the plane (cf. figure 4).…”

The ejection of large non-oscillating droplets from a hydrophobic wedge in microgravity

“…In the case of puddle jumping employed as a method to deploy large drops in low- g environments for further research, many interesting phenomena related to that process can be studied. The behavior of recoiling non-wetting moving contact lines, inertial contact lines 14 , highly inertial nonlinear capillary surface oscillations, analogies to droplet rebound phenomena, and numerical method benchmarking are a few such studies. The puddle jumping method is particularly useful in drop tower tests due to its simple implementation.…”

Droplet Impact on Surfaces with Asymmetric Microscopic Features

“…The contact line friction coefficient can be measured experimentally − or estimated by parameter fitting of numerical simulations to experiments. , Steen , recently used driven droplet oscillations to estimate the magnitude of the contact line friction coefficient. The values of the line friction parameter in previous studies are in the order of 0.1 Pa·s for water and increase in proportion to the square root of the liquid viscosity up to ∼1 Pa·s. ,, Since μ f is significantly larger than liquid viscosity for most aqueous solutions, ,, the contact line friction plays a particularly dominant role in dynamic and forced wetting applications.…”