Thesis (Ph. D.) University of Rochester. Department of Chemical Engineering, 2018.
A requirement for producing fusion energy is the availability of inexpensive fuel capsules. As researchers determine methods to make the fusion process more efficient, the demand for capsules will increase. This dissertation discusses a microfluidics approach using electric fields to produce emulsion droplets and transform them into capsule shells in a continuous process. The goal is to produce shells of high quality with a high throughput. Special attention was given to controlling the size of the droplets; one of which forms the shell wall while another determines the size of the capsule.
Electrowetting-on-dielectric (EWOD) and dielectrophoresis (DEP) forces were used to move conductive and dielectric fluids, respectively. It was demonstrated that water droplets containing a surfactant can be formed using the EWOD force and heating. The droplets had volumes ranging from 0.4 μL to 13 μL, and the variability in the droplet volume was 1 to 5% when a high heater power was used. In addition, oil droplets of various viscosity were dispensed with volumes ranging from 8 nL to 11 μL. The variability in the droplet volume was 2 to 15 % depending on the substrate geometry.
The dispensing experiments were supplemented by force modeling.
Combining the droplets formed emulsions ranging in volume from 0.2 μL to 16 μL. It was demonstrated that no surfactant was required to form water-in-oil emulsions. Moreover, using a high surfactant concentration allowed oil-in-water emulsions to form. A Gibbs free energy analysis was conducted to determine the effect of surfactant concentration on emulsion formation.
Once the emulsions were formed, they were transported between parallel plates using the EWOD force. The excitation sequence for the electrodes depended on the
emulsion type, the fluids used, and the size of the electrodes. As part of an effort to transport the emulsions to a space with a plate spacing suitable for making capsule shells, large droplets were moved between diverging plates down an inclined surface using gravitational and electrical forces. These forces were adequate to overcome capillary and surface pinning forces that prevented the droplet from moving to a wider plate separation.
To determine if emulsions could be transformed into capsule shells, droplets containing the chemicals required to form polystyrene shells were pipetted into an oil bath. The chemicals were photo-polymerized with ultraviolet light. An electric field was then applied between two electrodes surfaces to center a styrene-based double emulsion.