ORIGINS OF THE COMPLEX MOTION OF ADVANCING SURFACTANT SOLUTIONS

We have examined the fundamental mechanisms which drive the varied beh aviors of advancing surfactant solutions. We show that surfactant conc entration gradients and solution mobility are required for dendritic s preading, which occurs when an ionic surfactant,spreads on a surface o f the same charge. When the surfactant has the opposite charge as the ionized substrate, it can strongly adsorb to the surface ahead of the advancing solution. Inhibition of the fluid advance by surfactant-adso rption at the contact line alters the dendritic pattern and can change the spreading to stick-jump motion. By tuning the strength of the sur factant-surface interaction, we have observed a spectrum of spreading behaviors from dendritic to stick-jump.