REORIENTATION OF ACRIDINE-ORANGE IN A SODIUM DODECYL-SULFATE MONOLAYER AT THE WATER HEXADECANE INTERFACE

A macroscopically oriented layer of sodium dodecyl sulfate (SDS) at the interface of water and n-hexadecane was investigated using acridine orange as a fluorescent probe. The range of angles through which the hindered out-of-plane reorientation occurs for the probe was found to correspond closely to the surface roughness predicted by the capillary wave model through the interfacial tension. The in-plane reorientation of the probe was found to be significantly slower than that in the absence of SDS, with little dependence on the SDS concentration. The in-plane and out-of-plane rotations of acridine orange appear to correspond to the two decay components measured for acridine orange in micellar solution, indicating that these macroscopically oriented surfactant monolayers can provide detailed insight into solute-micelle interactions. For SDS micelles, the behavior of the oriented interface suggests that the surfactants are aggregated with the probe in the micelle and that the SDS micellar surface is very rough.