title: AC electrified jets in a flow-focusing device: Jet length scaling.
abstract: We use a microfluidic flow-focusing device with integrated electrodes for controlling the production of water-in-oil drops. In a previous work, we reported that very long jets can be formed upon application of AC fields. We now study in detail the appearance of the long jets as a function of the electrical parameters, i.e., water conductivity, signal frequency, and voltage amplitude. For intermediate frequencies, we find a threshold voltage above which the jet length rapidly increases. Interestingly, this abrupt transition vanishes for high frequencies of the signal and the jet length grows smoothly with voltage. For frequencies below a threshold value, we previously reported a transition from a well-behaved uniform jet to highly unstable liquid structures in which axisymmetry is lost rather abruptly. These liquid filaments eventually break into droplets of different sizes. In this work, we characterize this transition with a diagram as a function of voltage and liquid conductivity. The electrical response of the long jets was studied via a distributed element circuit model. The model allows us to estimate the electric potential at the tip of the jet revealing that, for any combination of the electrical parameters, the breakup of the jet occurs at a critical value of this potential. We show that this voltage is around 550 V for our device geometry and choice of flow rates.
authors.affiliation: Área de Mecánica de Fluidos, Departamento de Ingeniería Aeroespacial y Mecánica de Fluidos, Universidad de Sevilla , Avenida de los Descubrimientos s/n, 41092 Sevilla, Spain.
authors.forename: Elena
authors.identifier: 0000-0002-9990-1161
authors.initials: E
authors.lastname: Castro-Hernández
authors.affiliation: Departamento de Electrónica y Electromagnetismo, Facultad de Física, Universidad de Sevilla , Avenida de Reina Mercedes s/n, 41012 Sevilla, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: García-Sánchez
authors.affiliation: Área de Mecánica de Fluidos, Departamento de Ingeniería Aeroespacial y Mecánica de Fluidos, Universidad de Sevilla , Avenida de los Descubrimientos s/n, 41092 Sevilla, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Alzaga-Gimeno
authors.affiliation: Queensland Micro- and Nanotechnology Centre, Griffith University , Brisbane QLD 4111, Australia.
authors.forename: Say Hwa
authors.identifier: 0000-0002-9764-7868
authors.initials: SH
authors.lastname: Tan
authors.affiliation: CNRS, Univ. Bordeaux , CRPP, UPR 8641, Soft Micro Systems, 115 Avenue Schweitzer, 33600 Pessac, France and Max-Planck Institute for Dynamics and Self-Organization, Droplets, Membranes and Interfaces, Am Fassberg 17, DE-37077 Goettingen, Germany.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Baret
authors.affiliation: Departamento de Electrónica y Electromagnetismo, Facultad de Física, Universidad de Sevilla , Avenida de Reina Mercedes s/n, 41012 Sevilla, Spain.
authors.forename: Antonio
authors.identifier: 0000-0002-2190-1188
authors.initials: A
authors.lastname: Ramos