KINETICS OF METAL-ION COMPLEX-FORMATION IN MICELLAR MEDIA - A COMPARISON BETWEEN NORMAL AND POLYMERIZED MICELLES

Micellar media can be used to investigate the rate of complex formatio n between hydrophobic extractants and metal ions. Acceleration or reta rdation effects may be obtained, depending on factors such as the natu re of the surfactant, the hydrophilic/lipophilic character and ionizat ion state of the extractant, etc. The present work was aimed at studyi ng the influence of some specific parameters in producing retardation effects, which have potential application for performing separation of metal ions on a kinetic basis. The stopped-how technique was used to measure the rate of complex formation between Cu-2 divided by and comp lexing agents with varying alkyl chain length. Micelles made of the no nionic surfactants C(12)EO(6), Triton X-100 and Brij 35 were first con sidered, which did not show any direct correlation between the rate of complex formation and the thickness of the hydrophilic layer constitu ted by the polar heads of the surfactant molecules. In a second approa ch, we have used polymerized micelles obtained from undec-10-enyltrime thyl ammonium bromide, which we assumed to be more rigid than normal m icelles. Although the absence of CMC was confirmed, the rates measured in these polymerized micelles were larger than those obtained in mice llar solutions of CTAB and DTAB. The results are discussed in relation with the nature of the hydrophobic domains in the different situation s.