Droplet Self-Propulsion on Slippery Liquid-Infused Surfaces with Dual Lubricant Wedge-Shaped Wettability Patterns

Michele Pelizzari, Glen McHale*, Steven Armstrong, HONGYU ZHAO, Rodrigo Ledesma Aguilar, Gary Wells, Halim Kusumaatmaja

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Young's equation is fundamental to the concept of the wettability of a solid surface. It defines the contact angle for a droplet on a solid surface through a local equilibrium at the three-phase contact line. Recently, the concept of a liquid Young's law contact angle has been developed to describe the wettability of slippery liquid-infused porous surfaces (SLIPS) by droplets of an immiscible liquid. In this work, we present a new method to fabricate biphilic SLIP surfaces and show how the wettability of the composite SLIPS can be exploited with a macroscopic wedge-shaped pattern of two distinct lubricant liquids. In particular, we report the development of composite liquid surfaces on silicon substrates based on lithographically patterning a Teflon AF1600 coating and a superhydrophobic coating (Glaco Mirror Coat Zero), where the latter selectively dewets from the former. This creates a patterned base surface with preferential wetting to matched liquids: the fluoropolymer PTFE with a perfluorinated oil Krytox and the hydrophobic silica-based GLACO with olive oil (or other mineral oils or silicone oil). This allows us to successively imbibe our patterned solid substrates with two distinct oils and produce a composite liquid lubricant surface with the oils segregated as thin films into separate domains defined by the patterning. We illustrate that macroscopic wedge-shaped patterned SLIP surfaces enable low-friction droplet self-propulsion. Finally, we formulate an analytical model that captures the dependence of the droplet motion as a function of the wettability of the two liquid lubricant domains and the opening angle of the wedge. This allows us to derive scaling relationships between various physical and geometrical parameters. This work introduces a new approach to creating patterned liquid lubricant surfaces, demonstrates long-distance droplet self-propulsion on such surfaces, and sheds light on the interactions between liquid droplets and liquid surfaces.

Original languageEnglish
Pages (from-to)15676-15689
Issue number44
Early online date24 Oct 2023
Publication statusPublished - 7 Nov 2023

Keywords / Materials (for Non-textual outputs)

  • Composites
  • Contact Angle
  • Lipids
  • Liquids
  • Wetting


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