Investigation of the micellar properties of the tocopheryl polyethylene glycol succinate surfactants TPGS 400 and TPGS 1000 by steady state fluorometry.

This study has investigated the micellar properties of the d-alpha-tocopheryl polyethylene glycol succinate esters 400 (TPGS 400) and 1000 (TPGS 1000) in terms of critical micellar concentration (CMC), apparent aggregation number (N(agg)), microviscosity and micropolarity using steady state fluorescence techniques and fluorescent probes. In addition it has compared these properties against those of a Triton-type surfactant such as Triton X-100. The CMC values for TPGS 400, TPGS 1000 and Triton X-100 were 1.51 mM, 0.02 mM and 0.19 mM, respectively. The N(agg) values for TPGS 1000 and Triton X-100 were, respectively, 10 and 63. Due to the cloudiness of its aqueous solutions, no attempt was made to evaluate the microviscosity and to obtain the N(agg) for TPGS 400. Microviscosity at the probe site for all three surfactants was high and rather similar in spite of differences among their CMC values. The ability of TPGS 400 and TPGS 1000 to provide an environment for the fluorescence quenching of micelle-solubilized pyrene appears to be associated with their hydrophobic aromatic domains. To our knowledge the present study is the first attempt at systematically studying the micellar properties of the two most widely used TPGS compounds and of comparing these properties against each other and against those of an established nonionic surfactant.