The effect of staging of fluidic oscillation on microbubble generation in viscous liquids

Microbubbles are broadly defined as gas–liquid interfaces smaller than 1 mm and larger than 1 μm. Conventional modes of microbubble generation (ultrasound, ablative technologies, and electrolytic mechanisms) requires large amounts of energy and generate a wide distribution of microbubbles. Fluidic oscillation is an energy-efficient technique used for microbubble generation capable of generating a fairly monodisperse population of microbubbles compared to conventional bubbling. This study hypothesises that partial liquid wetting of membrane pores further benefits microbubble production. The partial liquid wetting can be introduced by utilising the ‘off’ portion of the fluidic oscillator, resulting in liquid imbibition. This liquid imbibition temporarily changes the membrane dynamics with intrapore wetting by the liquid. Therefore, using steady flow immediately after this operation would result in a similar behaviour (smaller bubble size) temporarily. This results in an interesting interplay between the two conditions—conventional bubbling (steady flow) and oscillatory flow, thereby presenting an intermediate condition with an associated reduction in bubble size when staged appropriately, i.e., for steady flow bubbling post-fluidic oscillator application. The resultant average bubble size is 25% lower than the steady flow bubbling prior to fluidic oscillation application but is dependent on physico-chemical properties: primarily viscosity and wetting angle. An intermediary condition is set based on the staging resulting in a 25–50% reduction in bubble size from steady-flow dynamics post-application of the oscillatory flow.