Resumen:
Surfactant films at the air-water interface are molecularly thin films that may show phase coexistence and can be transferred to different substrates. Knowing the phase diagram of a pure surfactant or a mixture permits films to be designed with different textures, and consequently with different rheological and electrostatic properties. In this Chapter, we will review how to generate a two-phase surfactant film and how to manipulate the distribution of each phase in order to achieve a special distribution of the phases. Furthermore, we will analyze the consequences of phase-coexistence and of the distribution of the phases at the film plane on the interface properties.