The Phenomenon of Sustained Bouncing: Silicone Oil Droplet Defies Surface Tension on a Vibrating Solid

Scientists affiliated with the Laboratory of Soft Interfaces Engineering Mechanics at the École Polytechnique Fédérale de Lausanne (EPFL) have achieved a significant milestone in the study of fluid dynamics. They successfully demonstrated, through experimental observation, that a droplet of silicone oil, measuring precisely 1.6 millimeters, can maintain a continuous rebound from a vibrating solid surface for a duration of five minutes—and potentially even longer. This groundbreaking experiment, conducted under standard room temperature conditions, fundamentally broadens the current scientific understanding regarding the complex interactions between liquids and solid materials.

What sets this accomplishment apart from earlier studies is the critical use of an atomically smooth mica plate as the supporting substrate, rather than the vibrating liquid bath required in previous long-duration bouncing observations. The research team established that the droplet’s subsequent motion—whether it exhibited a rhythmic, basketball-like bounce or a rapid glide atop an air cushion—was entirely governed by precise adjustments to the vibration frequency and amplitude settings. To provide scientific rigor to their findings, the team developed a coupled linear spring model capable of accurately predicting the rebound trajectories based on the inherent deformation of the droplet itself. These compelling results have been formally documented and published in the prestigious journal, "Physical Review Letters."

This observed effect functions as a kinetic counterpart to the well-known Leidenfrost effect, where a vapor layer forms a stabilizing cushion beneath a liquid drop on a hot surface. In this novel setup, however, the kinetic forces generated by the vibration of the solid substrate are what stabilize this macroscopic phenomenon over an astoundingly long period. The researchers noted a particularly fascinating scenario: when the second spherical harmonic mode was excited, the droplet transitioned into a "bound state," fixing its movement precisely above a thin layer of air. This observation underscores the crucial role played by the fluid’s internal structure and its capacity for self-deformation in sustaining this controlled and prolonged "dance."

The practical implications of this discovery are considerable, particularly for high-precision sectors such as the pharmaceutical industry. The ability to precisely manipulate infinitesimal volumes of liquid suspended in an air environment, free from the risks of contamination or premature evaporation, paves the way for innovative microdosing technologies. Demonstrating the immediate applicability of their work, the EPFL investigators successfully achieved lateral control over the droplet’s movement. They accomplished this feat by employing "tweezers" constructed from tiny jets of compressed air, thereby proving the feasibility of actively directing these microscopic fluid processes.