surfactant

Definition: a linear molecule with a hydrophilic (attracted to water) head and a hydrophobic (repelled by water) end. Surfactants tend to clump together when in solution - forming a surface between the fluid and air with the hydrophobic tails in the air and the hydrophilic heads in the fluid. Often surfactants will form "bubbles" within the fluid - a small sphere of heads surrounding a pocket of air containing the tails. They can also form bubbles in air - two nested spheres of surfactant, between them a thin layer of water, surrounding a pocket of air - and antibubbles in fluid - a layer of air surrounding a pocket of water.