Abnormal wetting dynamics of Silwet-laden droplets on partially wetting substrates

Karthik Nuthalapati, Yu Jane Sheng, Heng Kwong Tsao

Research output: Contribution to journalArticlepeer-review

Abstract

Silwet L-77 surfactant has the unique ability to spread water droplets across surfaces to a greater extent than conventional surfactants within a second. By using Silwet, the N,N-dimethylformamide (DMF) droplets can exhibit self-propulsion on a glass substrate. The peculiar wetting dynamics of the Silwet-laden DMF droplets was explored on the partially wetting substrates, including the polytetrafluoroethylene slide and slippery liquid-infused porous surface with negligible contact angle hysteresis (CAH). The time evolution of the contact angle (CA) was monitored for both high and low Silwet concentrations. Moreover, the volume inflation/deflation method and inclined plane method were employed to investigate the CA relaxation. The sessile droplet exhibits long-time wetting dynamics and it spreads very slowly, depending on the Silwet concentration. The dynamic CA decreases for more than 20 min at low Silwet concentrations (e.g., 1 wt%), but the droplet reaches its equilibrium state within 4 min at high concentrations (e.g., 10 wt%). The relaxation behavior is also influenced significantly by CAH which is found to impede the initial CA relaxation. Finally, the abnormal wetting dynamics is explained by the time-varying interfacial tensions according to Young's equation.

Original languageEnglish
Article number129381
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume648
DOIs
StatePublished - 5 Sep 2022

Keywords

  • Dynamic contact angle
  • N
  • N-dimethylformamide
  • Partially wetting surface
  • Silwet L-77
  • Wetting dynamics

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