EFFECT OF CROWN-ETHER 1,4,7,10,13,16-HEXAOXACYCLOOCTADECANE ON THE STRUCTURE OF SODIUM DODECYL-SULFATE AND DODECYLTRIMETHYLAMMONIUM BROMIDEAQUEOUS MICELLAR SOLUTIONS

The effects of the addition of crown ether 1,4,7,10,13,16-hexaoxacyclo octadecane on the structure of aqueous solutions of surfactants sodium dodecyl sulfate and dodecyltrimethylammonium bromide have been studie d by small angle neutron scattering. By modeling the scattering intens ities, it was possible to derive, simultaneously, both structural prop erties and information on the distribution of crown ether between the micellar and aqueous phases. In the case of sodium dodecyl sulfate, an appreciable amount of crown ether was found to be localized in the mi cellar phase, though it was not possible to establish whether it was i n the core or in the shell; there was no evidence of crown ether local ization in dodecyltrimethylammonium bromide micelles. The above observ ations indicate that although, at least in principle, the crown ether methylene groups could interact hydrophobically in the micellar core w ith the surfactant alkyl chains, the ability of crown ethers to form m etal complexes might also lead, in sodium dodecyl sulfate solutions, t o electrostatic interactions in the external palisade between the crow n ether-sodium ion complex and the surfactant head groups. The absence of crown ether from dodecyltrimethylammonium bromide micelles indicat es that the macrocyclic molecules interact with sodium dodecyl sulfate micelles via the formation of a complex between the sodium ion and th e crown ether and rules out the possibility of hydrophobic interaction in the micellar core.