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Oil-in-Water fL Droplets by Interfacial Spontaneous Fragmentation and Their Electrical Characterization

Arrabito, Giuseppe, Errico, Vito, De Ninno, Adele, Cavaleri, Felicia, Ferrara, Vittorio, Pignataro, Bruno, Caselli, Federica
Langmuir 2019 v.35 no.14 pp. 4936-4945
air, droplets, electric impedance, emulsions, microelectrodes, nonionic surfactants, oils, organ-on-a-chip, polysorbates
Inkjet printing is here employed for the first time as a method to produce femtoliter-scale oil droplets dispersed in water. In particular, picoliter-scale fluorinated oil (FC40) droplets are printed in the presence of perfluoro-1-octanol surfactant at a velocity higher than 5 m/s. Femtoliter-scale oil droplets in water are spontaneously formed through a fragmentation process at the water/air interface using minute amounts of nonionic surfactant (down to 0.003% v/v of Tween 80). This fragmentation occurs by a Plateau–Rayleigh mechanism at a moderately high Weber number (10¹). A microfluidic chip with integrated microelectrodes allows droplets characterization in terms of number and diameter distribution (peaked at about 3 μm) by means of electrical impedance measurements. These results show an unprecedented possibility to scale oil droplets down to the femtoliter scale, which opens up several perspectives for a tailored oil-in-water emulsion fabrication for drug encapsulation, pharmaceutic preparations, and cellular biology.