Thesis
The role of surfactant and pair interactions in leaky dielectric drop electrohydrodynamics
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2026
- Thesis identifier
- T18170
- Person Identifier (Local)
- 202152628
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- When a weakly conducting (leaky dielectric) drop is suspended in another fluid and exposed to a uniform DC electric field, a charge distribution develops on the interface of the drop due to the discontinuity of the electrical properties there. This charge distribution leads to electric stresses on the interface, which drive both fluid motion and deformation of the drop. This thesis explores two aspects of this challenging electrohydrodynamic problem, namely the effects of the presence of surfactant on the behaviour of a single drop and the effects of interactions on the behaviour of a pair of clean drops. We present semi-analytical theories built within the framework of the Taylor–Melcher leaky dielectric model assuming small drop deformations and large viscosity ratios. Specifically, we derive systems of coupled nonlinear ordinary differential equations which are solved numerically using a fourth-order Runge–Kutta time-stepping scheme and a pseudo-arclength continuation algorithm. The novelty of our theories lies in the retention of surface charge convection, which couples the interfacial charge to the flow fields in a nonlinear fashion and precludes closed-form solutions to the governing equations, but which it is necessary to include if one wishes to capture the transition to Quincke rotation, a symmetry-breaking instability in which the drop begins to rotate spontaneously when the electric field strength is greater than a critical value. We first briefly explore an isolated clean drop, for which we discuss the experimentally observed hysteresis at the onset of Quincke rotation, and derive an expression for the critical field strength for the onset of Quincke rotation of a spherical drop. For the problem of a surfactant-laden drop, we find that the presence of a weakly-diffusing surfactant on the drop interface can eliminate this hysteresis and significantly decrease the critical field strength, and we systematically explore the effects of varying the surfactant diffusivity and the sensitivity of the surface tension to the local surfactant concentration on the rotation of a drop. For the problem of a pair of interacting clean drops, we report qualitatively different types of trajectories followed by pairs of interacting drops undergoing Quincke rotation and explore the effects of interactions on the deformation, tilt angle, and angular velocity of pairs of fixed drops as the alignment of the drop pair relative to the electric field is varied. By exploring the behaviour of drops in these two new contexts, this thesis extends our understanding of droplet electrohydrodynamics, particularly with regard to Quincke rotation, and opens up several promising avenues for future research.
- Advisor / supervisor
- Das, Debasish
- Wilson, Stephen
- Resource Type
- DOI
Relations
Items
| Thumbnail | Title | Date Uploaded | Visibility | Actions |
|---|---|---|---|---|
|
|
PDF of Thesis T18170 | 2026-10-12 | Public | Download |