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DY: Fachverband Dynamik und Statistische Physik

DY 50: Wetting, Droplets, and Microfluidics (joint session DY/CPP)

DY 50.10: Talk

Thursday, March 21, 2024, 17:30–17:45, BH-N 334

Extracting oil from an oil and water mixture by using their different wetting properties via the Acoustowetting phenomenon — •Ofer Manor — Technion - Israel Institute of Technology, Haifa, Israel

The free surface of an oil in water emulsion usually catalyzes the formation of a thermodynamically favorable oil film far before the emulsion destabilizes in the bulk of the mixture: We stabilize 170 nm nano-emulsions by surfactants---SDS or Tween 20. The emulsions remain stable for 12 months in closed vessels. However, micron thick oil films appear within minutes on 10 micro-liter sessile drops of the emulsions. We extract the micron-thick oil film off the free surface of the emulsion drops using a traveling 20 MHz-frequency surface acoustic wave (SAW) in the solid.

In our experiments, we place drops of emulsion atop a lithium niobate substrate that supports a traveling SAW therein. Oil films leaks off the emulsion sessile drops 1-20 minutes from the commencement of the experiment, dynamically wetting the solid under acoustic stress---the Acoustowetting phenomenon. The Acoustowetting phenomenon discriminates between the water and oil phases via their wetting properties: The SAW powers the dynamic wetting of the solid by the oil film, extracting oil mass off the emulsion drops, while keeping the higher surface-energy water phase in place. The thickness of the oil film, leaking off the drops, oscillates between 20 to 1 microns and sustains a crystal-like pattern of lateral micron dimensions and submicron thickness of unknown origin in the presence of the SAW.

Keywords: wetting; emulsion; phase separation; surface acoustic wave; film dynamics