Evaporation and Electrowetting of Sessile Droplets on Slippery Liquid-like Surfaces and Slippery Liquid-Infused Porous Surfaces (SLIPS)

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Abstract

Sessile droplet evaporation underpins a wide range of applications from inkjet printing to coating. However, drying times can be variable and contact-line pinning often leads to undesirable effects, such as ring stain formation. Here, we show voltage programmable control of contact angles during evaporation on two pinning-free surfaces. We use an electrowetting-on-dielectric approach and Slippery Liquid-Infused Porous (SLIP) and Slippery Omniphobic Covalently Attached Liquid-Like (SOCAL) surfaces to achieve a constant contact angle mode of evaporation. We report evaporation sequences and droplet lifetimes across a broad range of contact angles from 105°-67°. The values of the contact angles during evaporation are consistent with expectations from electrowetting and the Young-Lippmann equation. The droplet contact areas reduce linearly in time and this provides estimates of diffusion coefficients close to the expected literature value. We further find that the total time of evaporation over the broad contact angle range studied is only weakly dependent on the value of the contact angle. We conclude that on these types of slippery surfaces droplet lifetimes can be predicted and controlled by the droplet’s volume and physical properties (density, diffusion coefficient, and vapor concentration difference to the vapor phase) largely independent of the precise value of contact angle. These results are relevant to applications, such as printing, spraying, coating and other processes, where controlling droplet evaporation and drying is important.
Original languageEnglish
Pages (from-to)11332–11340
JournalLangmuir
Volume36
Issue number38
Early online date3 Sep 2020
DOIs
Publication statusPublished - 29 Sep 2020

Keywords

  • EVAPORATING DROPLETS
  • electrowetting on dielectric (EWOD)
  • SLIPS
  • SOCAL

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