Celestial foam

Sea foam on the sand, a spoon in a chocolate mousse, a cosmetic cream applied to the skin: although foams are found everywhere, they are still poorly understood. Using air, some soapy water and a recipient with a rugged inner lining, this experiment aims to understand the mechanisms at work when a foam comes into contact with a rough surface. The separation between two bubbles is marked by a soap film; when three of them join up they form a Plateau border (in grey); and when the latter meet in fours they create a vertex (the bright spots). By dipping a glass slide into this dry liquid foam, the scientists are attempting to measure the force exerted on the plate and capture the movement of bubbles in contact with the recipient. This image is one of the winners of the 2022 La preuve par l’image (LPPI) photography competition.