Studies of Levitated Single Droplets

Citation

Chan, Chak Keung (1992) Studies of Levitated Single Droplets. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7q3j-q875. https://resolver.caltech.edu/CaltechETD:etd-07232007-131610

Abstract

The electrodynamic balance is a very unique and versatile device to study single particles. In-situ measurements of particles in a well characterized and controlled environment are possible. Supersaturated solutions can also be studied. In this research, its applications in studying light scattering, water activities and evaporation kinetics of single droplets are demonstrated. In particular, we studied the elastic and Raman scattering of an evaporating NaNO3 droplet. Different types of size dependent optical resonance structures were identified. The strongest Raman signal received was due to internal resonance of the excitation beam, giving similar enhancements to all Raman emissions. The intensity ratio of Raman nitrate to Raman water peaks can be used as a probe to semi-quantitatively characterize the droplet compositions. Water activities of mixed NH4NO3/(NH4)2SO4 aqueous solutions were also studied using the Spherical Void Electrodynamic Levitator. The compositional water activity data were used to evaluate the performance of three commonly used mixed electrolyte models: the Zdanovskii-Strokes-Robinson model, the Kusik and Meissner model, and the Pitzer model. They all predict droplet concentrations in mass fractions to a few percents error within the range where water activity data of single electrolytes are available. Evaporation of a few ceramic precursor solution droplets were investigated. While some precursor solutions crystallized, some others formed gels. Gel formation hindered further evaporation of water and the droplets exhibited a sharp decrease in evaporation rates. An approach to study rapid evaporation of droplets in the time scales of a few seconds was also demonstrated.

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