Abstract
The partitioned EDGE droplet generation device is known for its’ high monodisperse droplet formation frequencies in two distinct pressure ranges, and an interesting candidate for scale up of microfluidic emulsification devices. In the current study, we test various continuous and dispersed phase properties and device geometries to unravel how the device spontaneously forms small monodisperse droplets (6–18 μm) at low pressures, and larger monodisperse droplets (>28 μm) at elevated pressures. For the small droplets, we show that the continuous phase inflow in the droplet formation unit largely determines droplet formation behaviour and the resulting droplet size and blow-up pressure. This effect was not considered as a factor of significance for spontaneous droplet formation devices that are mostly characterised by capillary numbers in literature. We then show for the first time that the formation of larger droplets is caused by physical interaction between neighbouring droplets, and highly dependent on device geometry. The insights obtained here are an essential step toward industrial emulsification based on microfluidic devices.
Highlights
Emulsions are mixtures of two immiscible fluids, and form the basis of many products in e.g. the food, pharmaceutical, paint, and cosmetics industry
The current paper focusses on the production of oil-in-water emulsions, which is relevant for e.g. food production, it is good to mention that for biological and biomedicine applications, water-in-oil emulsions are often more relevant
Multiple microfluidic emulsification devices have been introduced in literature and most of them use the shear of the continuous phase to snap-off droplets from the to-be-dispersed phase (e.g. T- and Y-junctions, Flow-focussing and Co-flow devices)[7]
Summary
Emulsions are mixtures of two immiscible fluids (e.g. water and oil), and form the basis of many products in e.g. the food, pharmaceutical, paint, and cosmetics industry. Emulsions with a droplet size between 0.1–100 μm can be produced at very high production rates of over 20 m3 h−11,5, controlling droplet sizes is yet far from trivial with classic emulsification techniques, such as high pressure homogenizers and colloid mills[2] These technologies typically use only 1–5% of the total energy input to create interfaces, with the remainder dissipating into the system as heat, which is detrimental to heat sensitive components[2]. Multiple microfluidic emulsification devices have been introduced in literature and most of them use the shear of the continuous phase to snap-off droplets from the to-be-dispersed phase (e.g. T- and Y-junctions, Flow-focussing and Co-flow devices)[7] Their working mechanisms are relatively well-understood, and frequencies of several tens of kHz per droplet formation unit (DFU) have been recorded[16]. It was found that at relatively low dispersed phase pressures (
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