Microdroplet and –bubble formation
Bubbles and droplets with a well-controlled and narrow size distribution are important in several industrial and medical applications, e.g. in food industry the production of monodisperse powders through spray-drying results in a reduction of transportation and energy costs, in drug inhalation technology monodisperse droplets lead to an improved lung targeting, and in diagnostic ultrasound imaging monodisperse microbubbles can be used as ultrasound contrast agents.
In this project we study the formation of microdroplets through the spontaneous breakup of a microscopically thin liquid jets into droplets.
A liquid that is forced to flow through a nozzle at sufficient large velocity forms a jet that is inherently unstable. A small disturbance introduced by mechanical vibrations or thermal fluctuations will grow when its wavelength exceeds the jet’s circumference. The wave that grows fastest is the optimum wavelength for jet breakup and governs the droplet size. This phenomenon is known as “Rayleigh breakup”. We study the formation of these microdroplets using ultra high-speed microscopic imaging (Figure 1) and within a lubrication approximation model.
Figure 1: Time series of the breakup of a liquid jet into a continuous stream of micron-sized droplets. Ultra high-speed imaging was used for capturing microscopic images at 500.000 fps.
High-monodisperse microbubble formation is studied in microfluidic flow-focusing devices. The coflowing liquid squeezes the gas thread (black arrows in Figure 2) and a thin neck is formed, which collapses rapidly leading to the formation the microbubble. Soft lithography and micromoulding techniques are used to fabricate the flow-focusing devices in PDMS.
Figure 2: Schematic representation of a flow-focusing device for monodisperse microbubble production. Below: Snapshots of a high-speed recording showing the breakup of the gas thread.
Info: Detlef Lohse
|Role of the Channel Geometry on the Bubble Pinch-Off in Flow-Focusing Devices|
B. Dollet, W. van Hoeve, J.P. Raven, P. Marmottant, and M. Versluis
Phys. Rev. Lett. 100, 034504 (2008)BibTeΧ