LAUSR

Gels exhibit complex friction behavior. This study aims to evaluate the friction forces between two fractal agar gel substrates under sinusoidal motion to show the effect of rough surfaces on friction dynamics. In a previous study, we observed an asymmetric friction profile during reciprocating motion and an ultra-low friction state on flat agar gel surfaces. On the other hand, these distinct friction profiles were not observed on rough agar gel surfaces. We determined that this distinction was caused by the contact state between fractal agar gel surfaces; no thick water film was formed on the fractal surfaces because the rough structure provided channels to drain water from the interface. These physical insights are useful not only for developing biofunctional materials but also for understanding surface phenomena on biosurfaces including tongues and small intestinal walls.