Dynamics of formation and deposition of drops for MEMS applications
The formation and deposition of liquid drops in small volumes, viz., micro- and nano-scale free surface flows, are not only of fundamental scientific importance but also are vital for diverse engineering applications such as ink-jet printing, DNA and protein micro-/nano-arraying, and fabrication of particles and capsules for controlled release of drugs. The central focus of this thesis is to develop a comprehensive understanding of such free surface flows via high-speed imaging experiments and reliable and detailed (one-dimensional, 1D, or two-dimensional, 2D) Galerkin finite element (G/FEM) analysis. First, the dynamics of formation and breakup of single-fluid drops in succession (generally termed as "dripping") in a dynamically inactive or passive gas is analyzed both experimentally and computationally (1D). Second, the effects of soluble surfactants on the deformation and breakup dynamics of liquid bridges and drops are studied experimentally where the concentration of surfactant is varied below and above critical micelle concentration (cmc). Next, a rigorous and robust numerical (G/FEM) 2D algorithm is developed to analyze the effect of a monolayer of insoluble surfactant on the breakup dynamics of a single-fluid jet via a temporal analysis and to identify regions of parameter space that favor the formation of repeated or successive microthreads. Furthermore, a robust computational (G/FEM) 2D algorithm is developed to perform a temporal analysis of breakup of surfactant-laden two-fluid or the so-called compound jets (in a passive gas) and to identify regions of parameter space that favor successful micro-encapsulation. High-speed imaging experiments are also conducted to understand the breakup dynamics of drops in a quiscient immiscible ambient liquid that exerts a shear force on the inner liquid (unlike a dynamically inactive gas that exerts only a constant pressure on the inner liquid). Finally, the dynamics of drop impact on a substrate with a small-scale feature, viz., a rectangular well, is studied by means of high-speed imaging experiments and regions of parameter space that favor spreading and splashing are delineated in a phase diagram.
Basaran, Purdue University.
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