SPECTROSCOPIC PROBING OF THE INTERFACIAL ROUGHNESS OF SODIUM DODECYL-SULFATE ADSORBED TO A HYDROCARBON SURFACE

Acridine orange was used to probe the interfacial roughness of sodium dodecyl sulfate (SDS) adsorbed to a C18 monolayer in contact with vari ous premicellar aqueous solutions of SDS. The out-of-plane reorientati on of acridine orange reveals the amount of interfacial roughness. The results showed that the acridine orange adsorbs in a heterogeneous or ientational distribution that can be resolved into two components. One is a dynamic distribution that is attributed to high-frequency capill ary-like waves. The other is a static distribution that is attributed to a persistent structural interfacial roughness of the adsorbed SDS. Over the premicellar concentration range of SDS, the static orientatio nal distribution increases with increasing amounts of adsorbed surfact ant, reaching a sharp maximum at 7 mM, and then decreases.