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      Droplet migration characteristics in confined oscillatory microflows

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          Abstract

          We analyze the migration characteristics of a droplet in an oscillatory flow field in a parallel plate micro-confinement. Using phase filed formalism, we capture the dynamical evolution of the droplet over a wide range of the frequency of the imposed oscillation in the flow field, drop size relative to the channel gap, and the capillary number. The latter two factors imply the contribution of droplet deformability, commonly considered in the study of droplet migration under steady shear flow conditions. We show that the imposed oscillation brings in additional time complexity in the droplet movement, realized through temporally varying drop-shape, flow direction and the inertial response of the droplet. As a consequence, we observe a spatially complicated pathway of the droplet along the transverse direction, in sharp contrast to the smooth migration under a similar yet steady shear flow condition. Intuitively, the longitudinal component of the droplet movement is in tandem with the flow continuity and evolves with time at the same frequency as that of the imposed oscillation, although, with an amplitude decreasing with the frequency. The time complexity of the transverse component of the movement pattern, however, cannot by rationalized through such intuitive arguments. Towards bringing out the underlying physics, we further endeavor in a reciprocal identity based analysis. Following this approach, we unveil the time complexities of the droplet movement, which appear to be sufficient to rationalize the complex movement patterns observed through the comprehensive simulation studies. These results can be of profound importance in designing droplet based microfluidic systems in an oscillatory flow environment.

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          Droplet microfluidics.

          Droplet-based microfluidic systems have been shown to be compatible with many chemical and biological reagents and capable of performing a variety of "digital fluidic" operations that can be rendered programmable and reconfigurable. This platform has dimensional scaling benefits that have enabled controlled and rapid mixing of fluids in the droplet reactors, resulting in decreased reaction times. This, coupled with the precise generation and repeatability of droplet operations, has made the droplet-based microfluidic system a potent high throughput platform for biomedical research and applications. In addition to being used as microreactors ranging from the nano- to femtoliter range; droplet-based systems have also been used to directly synthesize particles and encapsulate many biological entities for biomedicine and biotechnology applications. This review will focus on the various droplet operations, as well as the numerous applications of the system. Due to advantages unique to droplet-based systems, this technology has the potential to provide novel solutions to today's biomedical engineering challenges for advanced diagnostics and therapeutics.
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            The biophysics and cell biology of lipid droplets.

            Lipid droplets are intracellular organelles that are found in most cells, where they have fundamental roles in metabolism. They function prominently in storing oil-based reserves of metabolic energy and components of membrane lipids. Lipid droplets are the dispersed phase of an oil-in-water emulsion in the aqueous cytosol of cells, and the importance of basic biophysical principles of emulsions for lipid droplet biology is now being appreciated. Because of their unique architecture, with an interface between the dispersed oil phase and the aqueous cytosol, specific mechanisms underlie their formation, growth and shrinkage. Such mechanisms enable cells to use emulsified oil when the demands for metabolic energy or membrane synthesis change. The regulation of the composition of the phospholipid surfactants at the surface of lipid droplets is crucial for lipid droplet homeostasis and protein targeting to their surfaces.
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              Author and article information

              Journal
              10.1103/PhysRevE.93.023106
              1509.03011

              Thermal physics & Statistical mechanics
              Thermal physics & Statistical mechanics

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