Contents lists available at ScienceDirect Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa Magnetic field induced motion of water droplets and bubbles on the lubricant coated surface Pritam Kumar Roy a , Edward Bormashenko a, *, Mark Frenkel a , Irina Legchenkova a , Shraga Shoval b a Ariel University, Engineering Faculty, Chemical Engineering, Biotechnology and Materials Department, P.O.B. 3, 407000, Ariel, Israel b Ariel University, Engineering Faculty, Department of Industrial Engineering and Management, P.O.B. 3, 40700, Ariel, Israel GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Wetting Oil-lubricated surfaces Magnetic field Diamagnetic liquid Bubble ABSTRACT Diamagnetic water droplets placed on the silicone-oil-lubricated solid surfaces were displaced by a permanent magnetic field ≅ B 0.4T. The motion was sensitive to the hydrophobicity of the solid surface. Maximal velocities ≅ − v 0.1 0.2 max mm s were registered on the silicone-oil-lubricated hydrophobic surfaces. The maximal velocities were insensitive to the volume of water droplets for the volumes in the range of < < V 2 μl 12μl . The maximal velocities of the droplets were also only slightly dependent on the thickness of the oil layer. A model of the motion of diamagnetic droplets driven by the permanent magnetic field is suggested. The qualitative model describes satisfactorily scaling of the experimental findings. The reported process involves purely diamagnetic materials. Motion of silicone oil bubbles driven by the magnetic field is also reported. 1. Introduction Magnetic control of displacement of micro- and nano-droplets is a powerful instrument of the precise control of motion of micro-vessels that can store chemical reagents, DNA/RNA, proteins and living cells/ microorganisms [1–3]. Magnetic micro- and nano-beads suspended in the liquid phase are usually used for the magnetically-controlled dis- placement of micro-vessels [1–3]. We demonstrate that diamagnetic droplets may be displaced by moderate magnetic fields (∼ 0.4 T) when placed on oil-impregnated hydrophobic surfaces. Thus, the use of the ferromagnetic or paramagnetic particles is avoided, which is of a primary importance for lab-n-chip applications. Wetting of flat and rough oil lubricated (impregnated) surfaces attracted the attention of investigators in the last decade [4–13]. Lubrication of solid rough and flat pre-wetted surfaces is ubiquitous in nature. Cartilage integrity, for example, is impossible without lubrication [14]. Study of the lubrica- tion occurring within cartilage inspired the research, and resulted in the development of efficient artificial lubricants mimicking natural ones [15]. Artificial lubricant-impregnated surfaces demonstrate the poten- tial for a diversity of industrial applications. They are obviously at- tractive for manufacturing omniphobic (superoleophobic) surfaces due to the fact that they do not suffer from Cassie-Wenzel wetting https://doi.org/10.1016/j.colsurfa.2020.124773 Received 16 December 2019; Received in revised form 23 March 2020; Accepted 24 March 2020 ⁎ Corresponding author. E-mail address: edward@ariel.ac.il (E. Bormashenko). Colloids and Surfaces A 597 (2020) 124773 Available online 02 April 2020 0927-7757/ © 2020 Elsevier B.V. All rights reserved. T