Non-Newtonian Drop Impact on Textured Solid Surfaces: Bouncing and Filaments Formation

• Main Author: Al Julaih, Ali
• Other Authors: Thoroddsen, Sigurdur T
• Language: en
• Published: 2021
• Subjects: drop impact; non-newtonian liquids; hydrophobic surfaces; polyethylene oxide; bouncing; filaments
• Online Access: Al Julaih, A. (2021). Non-Newtonian Drop Impact on Textured Solid Surfaces: Bouncing and Filaments Formation. KAUST Research Repository. https://doi.org/10.25781/KAUST-2E5IV; http://hdl.handle.net/10754/668998

This work uses high-speed video imaging to study the formation of filaments, during impact and rebounding of drops with polymer additives. We use PEO of different concentrations from 10 to 1000 ppm and study how drops rebound from various different surfaces: superhydrophilic, hydrophilic, hydrophobic, and superhydrophobic. Bouncing occurs for all surfaces at low impact velocities. We specifically focus on the phenomenon of the generation of polymer filaments, which are pulled out of the free surface of the drop during its rebounding from micro-pillared or rough substrates. We map the parameter regime, in terms of polymer concentration and impact Weber number, where the filaments are generated in the most repeatable manner. This occurs for regularly pillared surfaces and drops of 100 ppm PEO concentrations, where numerous separated filaments are observed. In contrast, for superhydrophobic coatings with random roughness the filaments tend to merge forming a branching structure. Impacts on inclined surfaces are used to deposit the filaments on top of the pillars for detailed study.