Electrostatic interaction between water droplets coated by cold-plasma-treated silicone oil. Quantification of cold plasmas charging of liquids

Significance Statement

Interaction of cold plasmas with organic liquids is a complicated process that includes diverse physicochemical events. One of such events is the charging of the surface of a liquid. This study is focused on the estimation of the surface density of electrical charge supplied by the cold radiofrequency air plasma to the silicone oil. Water droplets placed the surface of the plasma treated PDMS oil were used as probes. They were coated by plasma charged oil layers and repulsed one another via electrostatic interaction.

Electrostatic interactions are important when droplets as well as colloidal particles are placed at interfaces. They, together with capillary interactions, govern floating, surface orientation and self-assembly of colloidal particles. This paper is devoted to the electrostatic interactions of droplets, placed on the cold-plasma-treated polydimethylsiloxane (PDMS) oil surfaces. Liquid organic surfaces, as well as solid ones, are charged electrically negatively when exposed to the cold plasma treatment.

The researchers, Edward Bormashenko and his colleagues from the Ariel University in Israel, investigated the electrostatic interaction between water droplets, coated by cold-plasma-treated silicone oil, and quantified the surface charge density of the oil. Their work has been published in a peer-reviewed journal, Colloids and Surfaces A: Physicochemical and Engineering Aspects.

Polypropylene films were coated with honeycomb polycarbonate film with the fast dip-coating process. The use of honeycomb surfaces facilitated manufacturing stable silicone oil infused surfaces. The resulting substrate was covered with PDMS oil. The mentioned polycarbonate polymer patterns, covered with oil, were exposed to a radiofrequency inductive air cold plasma discharge. Two droplets were placed on the surfaces covered with plasma treated PDMS oil with a multichannel syringe. The water droplets were spontaneously encapsulated by PDMS, and when completely coated by plasma treated PDMS oil layers, they began to repel each other owing to the Coulomb repulsion. The displacement of the interacting water droplets was registered with the rapid camera. The researchers came up with a mathematical model of electrostatic interaction that enabled a rough estimation of the surface charge density, as σ≅1.0µC/m2. The surface charge density was independently estimated by electrostatic pendulum.

About The Author

Edward Bormashenko is a professor of chemical engineering and materials science and is the head of the Laboratory of Interface Science at Ariel University in Israel. His research interests include wetting phenomena, surface science, superhydrophobicity, wetting transitions, processes of self-assembly, polymer science, soft matter physics and interaction of plasma with organic materials.

He is the author of more than 200 publications in these fields, including the book Wetting of Real Surfaces and 14 registered patents. In the last decade, he has devoted his research to the interfaces with prescribed wettability, including non-wetted surfaces, nonstick droplets and self-propulsion.

About The Author

Evgeny Shulzinger is a PhD student at Physics Department of Ariel University, Israel. The title of his PhD research is “Study of processes of interaction of plasma with polymers”. He is the author of more than 25 publications. The fields of his research are FTIR spectroscopy, interaction of plasma with polymers, and wetting phenomena.

About The Author

G.E. Whyman works at Ariel University (Israel), Physics Department in a position of Associate Professor. Until 2004 he works in the field of Quantum Chemistry improving the methods of calculation of various properties of molecules. He has published the monograph devoted to the development of methods accounting foe electron correlation in molecules.

In the last decade, Prof. Whyman has performed theoretical research in the field surface science connected with wetting, superhydrophobicity, superoleophobicity etc. His list of publications includes more than 113 papers. The most cited works relate to justification of the existing methods of description of wetting states (Chemical Physics Letters 450 (4), 355-359) and with theoretical design of superhydrophobic reliefs (Langmuir 27 (13), 8171-8176).

About The Author

Victor Multanen is a PhD student at chemical engineering Department, Ariel University, Israel. Mr. Victor Multanen performs experimental research in the field of surface science connected with plasma treatment of surfaces, in particular with interaction of plasma with polymers. He is the author of more than 10 publications.

About The Author

Yelena Bormashenko works at The Authority for Research & Development in Ariel University (Israel), Chemical Engineering Department. Her scientific interests include superhydrophobicity and oleophobicity, wetting phenomena, polymer science, superhydrophobicity, processes of self-assembly. She is the author of more than 60 publications in these fields.

Journal References

Victor Multanen2, Evgeny Shulzinger1, Gene Whyman1, Yelena Bormashenko1,2, Edward Bormashenko1,2. Electrostatic interaction between water droplets coated by cold plasma treated silicone oil. Quantification of cold plasmas charging of liquids. Colloids and Surfaces A: Physicochem. Eng. Aspects 509 (2016) 224–228.

1 Ariel University, Natural Science Faculty, Physics Department, 407000, P.O.B. 3, Ariel, Israel.
2 Ariel University, Engineering Faculty, Chemical Engineering and Biotechnology Department, 407000, P.O.B. 3, Ariel, Israel.


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