Electrodynamic Levitator-Trap to Quasi-Electrostatic Levitator
for Microparticle Nucleation Studies
S. Arnold, N. Wotherspoon, and N.L. Goddard
Rev.Sci.Instrum. 70, 1473-77 (1999)
This article describes an apparatus for obtaining nucleation data from a levitated solution microdroplet, automatically. A particularly novel feature is that it uses an electrodynamic levitator trap (ELT) which converts to a quasielectrostatic levitator (QEL), at any time during an experiment. The conversion is accomplished by using asymmetrically applied potentials on the ELT structure. With this modification one can trap a particle in the ELT mode and then convert to the QEL mode for automatic operation. By eliminating the need for the alternating gradient forces which are intrinsic to the ELT, the system in its QEL mode is shielded from unwanted noise and parametric instabilities associated with the ELT's alternating potential. To test the system theoretically, we calculate the effect which molecular collisions have on the positional variance in a spherical void QEL. Following this, we describe the components of our servosystem, and demonstrate the robustness of our design by following the nucleation of a solution droplet as the ambient relative humidity is reduced by evacuation.