title: Drop formation via breakup of a liquid bridge in an AC electric field.
abstract: Experimental results are presented for the study of drop formation mechanism in a newly proposed electrohydrodynamic (EHD) method of drop generation in an AC electric field. In the method, a small drop is generated in two stages. A pendant drop is elongated with large oscillation by an electric force in the first stage. Then, it undergoes formation and breakup of a liquid bridge between the upper nozzle and the insulator-coated lower flat plate in the second stage. It is found that there exists a resonant frequency for maximum oscillation, which leads to an efficient drop formation in the latter stage. It is also found that breakup of liquid bridge is accelerated by the electrowetting tension acting on the drop perimeter contacting the insulator-coated flat plate. Thus the whole procedure of drop formation depends heavily on the frequency of AC field and the properties of the insulator such as hydrophilicity, thickness, and the dielectric constant. It is demonstrated that a wide range of drop size, from picoliter to nanoliter, can be obtained by controlling such key parameters without changing the nozzle diameter.
authors.affiliation: Department of Chemical Engineering/Division of Mechanical and Industrial Engineering, Pohang University of Science and Technology, San 31, Hyoja-Dong, Pohang, South Korea.
authors.forename: Beom Seok
authors.initials: BS
authors.lastname: Lee
authors.forename: Hye-Jung
authors.initials: HJ
authors.lastname: Cho
authors.forename: Jeong-Gun
authors.initials: JG
authors.lastname: Lee
authors.forename: Nam
authors.initials: N
authors.lastname: Huh
authors.forename: Jeong-Woo
authors.initials: JW
authors.lastname: Choi
authors.forename: In Seok
authors.initials: IS
authors.lastname: Kang
mesh_terms: D004247:DNA / Q000737:chemistry; D004566:Electrodes; D004574:Electromagnetic Fields; D020411:Oligonucleotide Array Sequence Analysis / Q000295:instrumentation / Q000379:methods; D009991:Oscillometry; D010316:Particle Size; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D004247:DNA