We observe a new phenomenon whereby spheres sediment and form a single, stable vertical stack in a yield-stress fluid. Individually, the spheres settle to the bottom, since the yield stress is insufficient to suspend a single sphere. However, cooperative effects result in surprisingly stable stacking. The fluid is composed of water with a small amount of additive (0.15 wt% of polymer microgel particles, Neutragel DA). This class of fluids, known as yield-stress fluids, are effectively solid at low stress though flow at high stress. Similar non-Newtonian behavior is used in everyday products like toothpaste and hand sanitizer, as well as in technological applications such as fire suppression and additive manufacturing. With this video, we aim to spark curiosity and interest into the intriguing world of yield-stress fluids in particular and non-Newtonian fluids in general.
This work is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License. Any reuse must credit the author(s) and provide a link back to this page.