Measurement of mechanical properties of liquid by observing droplet oscillation on substrates

Abstract

Abstract In this paper, we introduce a method to measure the surface tension of a droplet on a solid substrate by observing the resonance oscillation excited by applying Maxwell stress using electric field tweezers in a noncontact manner. Additionally, we measured the frequency spectrum of the oscillation amplitude using a stroboscopic imaging technique. The resonance frequency of the droplet was inversely proportional to the 3/2th power of the droplet radius, with a contact angle of approximately π/2 rad. The acquired result is in good agreement with the theory derived by extending the established formula for a free-sphere droplet. Furthermore, the contact angle dependence of the resonance frequency can be qualitatively explained based on the behavior of waves on a confined liquid surface.