Droplet Retention and Shedding on Slippery Substrates

Orme, Bethany, McHale, Glen, Ledesma Aguilar, Rodrigo and Wells, Gary (2019) Droplet Retention and Shedding on Slippery Substrates. Langmuir, 35 (28). pp. 9146-9151. ISSN 0743-7463

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Official URL: https://doi.org/10.1021/acs.langmuir.9b00931

Abstract

A significant limitation for droplet mobility on solid surfaces is to overcome the inherent pinning of the droplet’s contact line that occurs due to chemical/physical heterogeneities. A recent innovation is to use surface texture or porosity to create a stabilised lubricant surface. Droplets on such Slippery Liquid Infused Porous Surfaces/Lubricant Impregnated Surfaces (SLIPS/LIS) are highly mobile due to the lubricant layer. Low pinning of the contact line reduces the energy required to move a droplet, however, it makes it difficult to accurately position the droplet or to stop its motion altogether. In this paper, a simple structure (step), as small as a few microns in height, is used to introduce controlled droplet pinning on a slippery substrate. The key effect is identified as the capillary force, arising from the interaction between the lubricant menisci created by the step and droplet. The effect of changing step height, lubricant thickness and initial position on step-droplet interactions has been investigated, showing droplets can both be repelled from and attracted to the step. To measure the adhesion strength, we report droplet detachment angle measurements under gravity, and scaling of force with lubricant thickness/step height ratio. Under certain conditions, the interaction strength is sufficient to ensure droplet-step attachment even when the surface is rotated to an upside-down orientation. These findings presented can motivate the design of SLIPS structures, capable of shedding or retaining droplets preferentially, e.g., according to size or wettability, relevant to applications from microfluidics to fog harvesting.

Item Type: Article
Uncontrolled Keywords: Slippery Liquid-Infused Porous Surface, SLIPS, Lubricant Impreganted Surface, droplets, Cheerios Effect, wetting ridge, low pinning, wettability, menisci.
Subjects: F100 Chemistry
F200 Materials Science
H800 Chemical, Process and Energy Engineering
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Elena Carlaw
Date Deposited: 21 Jun 2019 09:57
Last Modified: 11 Oct 2019 10:01
URI: http://nrl.northumbria.ac.uk/id/eprint/39768

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