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.
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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