Experimental and theoretical research on oscillation behavior of droplets on horizontally oscillating substrates

The oscillation behavior of a droplet on a horizontally oscillating flat substrate was studied. We derived a formula to relate the resonance frequency and damping constant of the horizontal oscillation of the droplet to the physical properties of the liquid materials, which were examined experimentally. The resonance frequency and damping constant were expressed as functions of surface tension, droplet radius, contact angle, density, and viscosity. Furthermore, we observed the non-equilibrium phenomenon of the droplet through the adsorption of molecules from the surrounding gas phase onto the droplet surface. We demonstrated the time evolution of the surface tension of an ethanol aqueous solution, and the decrease in surface tension due to the evaporation of ethanol was detected using the newly developed system.