GROWTH OF NON-MODAL TRANSIENT STRUCTURES DURING THE SPREADING OF SURFACTANT COATED FILMS

The spreading of surfactant coated thin liquid films is often accompan ied by an instability producing significant film corrugation, fingerin g and branching. Marangoni stresses, responsible for the rapid and spo ntaneous spreading, are suspected as the main cause of unstable flow. Traditional eigenvalue analysis of a self-similar solution describing Marangoni driven spreading has predicted only stable modes. We present results of a transient growth study which reveals enormous amplificat ion of initially infinitesimal disturbances in the film thickness. Thi s analysis provides, for the first time, evidence of an instability re sembling experimental patterns. (C) 1998 American Institute of Physics .