Experimental study on droplet formation using a newtonian and a non-newtonian liquid flowing in a microchannel subject to an AC electric field

Abstract

The aim of this work is to experimentally investigate the electrohydrodynamic instability and droplet formation between two immiscible liquids flowing in a microchannel. When two immiscible liquids are pumped into a microchannel, a flat stable interface forms between them because of the laminar regime of the flow. If an external electric field is applied in a direction normal to the interface, the interface may deflect and deform. This phenomenon is called the electrohydrodynamic (EHD) instability and can be used for the generation and the manipulation of droplets. The volumes of droplets generated in this work are in the range of 0.4 to 1.5 μL. For the experiments in this study, handmade microchannels that are 1.10 mm in width and 0.36 or 0.55 mm in depth with an electrode length of 10 or 20 mm are used. For the investigation of the EHD instability between two Newtonian liquids, silicone oil with a kinematic viscosity of 50 cSt is used as the dispersed phase and ethylene glycol (EG) is used as the continuous phase; where the applied electric field is normal to the interface and in the range of 0.68 to 2.18 kV. For the EHD instability analysis for the interface between a Newtonian and a non-Newtonian liquid, the dispersed phase is kept the same and the continuous phase is replaced with a xanthan gum/aqueous glycerol solution; and the applied voltages are in the range of 0.54 to 2.73 kV. Finally, the formation of silicone oil droplets in the non-Newtonian phase and the droplet size dependency on the thickness ratio and the applied voltage are studied. The applied voltages for the generation of droplets are above the critical voltage of the system and range from 0.96 to 3.53 kV.