TEMPORAL AND SPATIAL DEVELOPMENT OF SURFACTANT SELF-ASSEMBLIES CONTROLLING SPREADING OF SURFACTANT SOLUTIONS

When a substrate is immersed into a solution of strongly adsorbing surfactant, the contact line advances by jumping forward along the surface. At low concentrations the contact line then retracts, exhibiting autophobic behavior. We have directly observed the development of the surfactant assemblies at the contact Line which cause these behaviors. Different macroscopic spreading behavior and microscopic development of the self-assembly occur above and below a bulk solution concentration of similar to 0.45cmc. These surfactant barriers ahead of the contact line exhibit two regions with distinctive structures and time evolutions. This structure ahead of the contact line combines with the surfactant on the solid-liquid interface to form a self-assembled surfactant structure which pins the advance of the contact line and causes stick-jump behavior. We put an upper limit on the size of the region on the solid surface relevant in determining the contact angles.