Electrohydrodynamics: a study of collective behavior and self-organization of an oil-in-oil emulsion

Tadavani, Somayeh Khajehpour (2018) Electrohydrodynamics: a study of collective behavior and self-organization of an oil-in-oil emulsion. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (5MB)

Abstract

In this thesis, I study the collective behavior and self-organization of immiscible silicone oil drops in a castor oil medium. Castor oil is a “leaky dielectric” and the silicone oil drops interact with each other due to electrohydrodynamic forces induced by an imposed electric field. The strength and the range of the hydrodynamic interactions are modulated by changing amplitude and frequency of the electric field, respectively, in a small capacitor. The result of the electrohydrodynamic forces is to induce flows that induce drop motions, deformations and breakup. I study the effect of cell thickness, d, on the size distribution and dynamics of silicone oil drops in presence of an external DC electric field. I also investigate the effect of dimensionality by varying the cell thickness, d, and observation of drop dynamics as well as the observation of an electrohydrodynamically driven convective instability. For the first time, to our knowledge, two-roll structures, with a lateral size that is half the cell thickness, are observed experimentally. Further, this instability is also seen in castor oil medium, in the absence of any liquid-liquid and solid-liquid interfaces, indicating the importance of electrokinetic effects. Next, I constrain the motion of silicone oil drops in 2D, using dielectrophoretic traps, in order to create a 2D droplet crystal. By driving this crystal with frequencytunable electrohydrodynamic forces, I construct a amplitude-frequency phase diagram for the non-equilibrium order to disorder phase transition of silicone oil drops in castor oil medium. The pure order-to-disorder behaviour is observed for a amplitudefrequency regime where no breakup events occur but the hydrodynamic flows are strong enough to deform and partially unpin the droplets from their trap potential. Finally, an examination of the underlying flows using tracer particles reveals anomalous superdiffusive motion with power law scaling of t3/2. The underlying probability distribution for these anomalous motions is non-Gaussian and has the form exp (-( x2 )δ/2 4Kγt3/2 At short times, it is a simple exponential decay (i.e. δ = 1), while at longer times the distribution is consistent with δ = 1.4. This system exhibits non-equilibrium self-organization that is frequency- and amplitude-tunable, that will not only allow more detailed comparisons with detailed theory and simulation in the future. Moreover, it has been demonstrated as a model system for studying self-organization with tunable hydrodynamic interactions.

Actions (login required)

View Item