Surfactants with ionizable heads are key to creating a repulsive force that counteracts the van der Waals attraction and thus stabilizes a soap film.

The new film is based on a book of the same name by Bryan Burrough, who says the FBI's pursuit of Dillinger and co - who all earned the title "public enemies" - became a "national soap opera".

Shampoo foam stability is thus promoted by an electrostatic double-layer repulsion of opposite sides of the soap film between neighboring bubbles.