MIXED MICELLAR AGGREGATES OF NONIONIC SURFACTANTS WITH SHORT HYDROPHOBIC TAILS

Mixed micelle formation by aq. mixts. of pentaethylene glycol monohexyl ether (C6E5) and diethylene glycol monohexyl ether (C6E2) has been investigated by detg. the temp.-compn. phase diagrams and measuring the intradiffusion coeffs. In binary aq. solns., C6E5 shows a high tendency to micellize, while C6E2, because of its too short hydrophilic head, presents a macroscopic phase sepn. in a water-rich and a surfactant-rich phases. The temp.-compn. phase diagrams obtained for the ternary water-C6E5-C6E2 mixts. present a micellar region in which both surfactants co-aggregate. The dimensions of this micellar region depend on the relative ratio between the two surfactants molalities. By analyzing the micelle intradiffusion coeff., measured through the PGSE-NMR technique, the hydrodynamic radius of the aggregates has been estd. at 25 °C. It is similar to that of triethylene glycol monohexyl ether (C6E3) in binary aq. soln. The exptl. evidences suggest that in mixed ethoxylated surfactants the micellar behavior is mainly detd. by the mean no. of ethoxylic units per surfactant mol., independently of their distribution.