Straight to zigzag transition of foam pseudo-Plateau borders on textured surfaces

The structure of liquid foams follows simple geometric rules formulated by Plateau 150 years ago. On smooth surfaces, the foam liquid channels, also called pseudo Plateau borders, are straight between vertices. We demonstrate experimentally that on rough surfaces and under some conditions that we establish, the bubble footprint exhibits a morphological transition. The footprint can adopt a zigzag shape between vertices. We rationalize the number of zigzag segments by a geometric distribution describing the observations made with the footprint perimeter and the mesh size of the asperities.