DIRECT VISUALIZATION OF SURFACTANT HEMIMICELLES BY FORCE MICROSCOPY OF THE ELECTRICAL DOUBLE-LAYER

The morphology of ionic surfactant molecules adsorbed from aqueous sol ution onto hydrophobic substrates has been determined by atomic force microscopy. Near the critical micelle concentration (cmc), noncontact imaging using double-layer repulsion between the tip and sample shows parallel, epitaxially oriented stripes spaced apart by about twice the surfactant length. This represents the first direct imaging of ''hemi micelles'', liquid-crystalline aggregates of amphiphilic molecules (an alogous to bulk micelles) which farm at interfaces. The striped patter n is indicative of hemicylindrical hemimicelles, which is further corr oborated by images of the monolayer adsorbate (in contact mode) below the cmc. Our results suggest that the hemimicelle structure is templat ed by the epitaxially bound monolayer, in contrast with previous inter pretations of the adsorption mechanism.