The structure of liquid foams follows simple geometric rules formulated by Plateau 150 years ago. By placing such foam on a microtextured hydrophilic surface, we show that the bubble footprint exhibits a morphological transition. This transition concerns the liquid channels, also called pseudo-Plateau borders, which are straight between vertices on a smooth surface. We demonstrate experimentally that for a sufficiently large roughness size compared to the width of the liquid channels, the footprint adopts a zigzag shape. This transition is associated with the absence of a wetting film between the pillars caused by capillary suction of the foam, observed by confocal microscopy. 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.

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• Distortions & defects
• Roughness
• Wetting
• Foams
• Confocal imaging
• Fluorescence