In Situ Observation of Crystallization Process of Single Levitated Microdroplet Using Electrodynamic Balance

Abstract

The electrodynamic balance (EDB), where a single charged aerosol can be levitated in space over the periods of hours, provides the opportunity for in situ observation of the suspended droplet. In this technical report, we describe a newly designed EDB system with a high resolution side-view imaging for the observation of a dynamic behavior of mixing state into droplet. A newly developed slim-type EDB consists of two coaxial cylinder electrodes (I.D. 6 mm and O.D. 8 mm) provided independently controlled the DC voltages superimposed on AC high voltage. Furthermore, the ground shield electrode (I.D. 14 mm and O.D. 15 mm) was installed in order to make the distance between levitated droplet and objective lens of optical microscope as close as possible. The shield electrode also played a significant role in preventing the discharge between the objective lens and a pair of cylindrical electrodes. With this instrument, we directly observed the crystallization processes of supersaturated sodium chloride and sodium bromide droplets in space. It is demonstrated that a newly designed EDB system can be a useful tool for understanding the role of internal mixing state of a droplet during the formation of solid particles.