Star-like breakup of polymeric drops in electrical field

The disintegration of liquid drops upon the impact with solid obstacles in presence of an electric field is investigated experimentally. Water and solutions of polyethylene oxide (PEO) and polyacrylamide (PAM) are used as tested liquids. We used a hydrodynamic configuration that reduces the viscous drag on the solid: a spherical drop impacted a small disk-like solid target. Impacting water drop formed a lamella, circular free film with a toroidal rim, which firstly increased in diameter, and then retracted with ejection of secondary droplets from the rim. The use of a disk-like target allowed performing a liquid/solid collision in the absence of liquid/solid viscous resistance. Polymeric additives did not influence the growth and the retraction rate. However they modified the disintegration process: thinning filaments were formed between secondary droplets and lamella rim, preventing the secondary drops detachment and the corresponding splashing. To impose an electric field on the lamella, a high positive voltage was applied directly to the steel disk-like target. The other ground pole was a cylindrical copper sheet located axisymmetrically with the disk-like target surrounding the target. As a result a radial electric field formed around the target and in the same time the target charged positively the liquid of the impacting drop. The potential difference between target and copper sheet was changed from zero up to 10 kV. Experiments showed that the applied voltage has no effect on the rate of lamella growth and retraction. Also no change was observed in the disintegration of very dilute (1 ppm) and very concentrated (10k ppm) polymer solutions. On the other hand new features of lamella disintegration could be initiated by high voltage in the intermediate range of concentrations. During breakup of drops of PEO of concentrations 10, 100 and tic ppm as well as of drops of PAM of concentration of 10 ppm, additional secondary filaments were ejected from the secondary droplets under the action of the electrical field. These secondary filaments are outward directed from the lamella centre and look thinner and longer than the primary polymeric filaments. As a result star-like liquid structures are formed. Wheel-like lamellas of 100 and 1k ppm PAM solutions become only slightly disturbed under the action of high electrical field. (C) 2015 Elsevier B.V. All rights reserved.