Stretching, bursting, splashing and bouncing: electrohydrodynamics of microfluidic drops
AffiliationChemical and Biomolecular Engineering
Document TypePhD thesis
Access StatusOpen Access
© 2017 Dr. Rohit Pillai
The technologies used to drive the miniaturisation of computers have had subsequent impact in other fields, and are now being used by researchers to shrink chemical/biological laboratories onto a single silicon-chip. Droplet-based `lab-on-a-chip' (LoC) devices use a microscale drop in lieu of a test-tube, converting the traditional steps involved in chemical-analysis to precise manipulations of the drop in a micron-sized channel. Typical drop manipulations in LoC devices include drop formation, fission, and fusion, which are commonly achieved by an applied electric field. While LoC devices can potentially revolutionise the chemical and life sciences, their development hinges on a fundamental understanding of electrically induced fluid-flow, or electrohydrodynamics, at the microscale. Using microfluidic drop manipulation in LoC devices as motivation, this thesis presents and analyses the results of a numerical investigation undertaken using a recently-developed, multiphase electrokinetic fluid-flow model. A large number of simulations were conducted for single-drop, drop-interface, and drop-drop systems, encompassing a wide range of physical, material, and electrical parameters. Despite their apparent simplicity, systems involving one or two electrified drops display rich and complex, but poorly understood, electrohydrodynamic phenomena. The objectives of the investigation were to: (i) identify the physical mechanisms responsible for the observed phenomena, (ii) develop qualitative phase-maps using the relevant parameters, and (iii) use this understanding in conjunction with scaling theory to quantitatively predict key output parameters, such as the size and charge of satellite drops formed during drop breakup, for example. The results from this work will inform the design, material selection, and operating conditions of electrohydrodynamic lab-on-a-chip devices. In addition, the insights developed into the physics of breakup/coalescence of microscale drops will be applicable to a wide range of related soft-matter systems.
Keywordscomputational fluid dynamics; electrokinetics; droplet dynamics; two-phase flow
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