ELECTRICAL STRUCTURE OF ((DODECYLOXY)METHYL)-18-CROWN-6 MICELLES IN AQUEOUS POTASSIUM-CHLORIDE SOLUTIONS - ELECTROPHORETIC LIGHT-SCATTERING AND 2D NMR

The zeta-potential of spherical mixed micelles of ((dodecyloxy)methyl)-18-crown-6 in 0.1 mol/dm3 KCl varies with temperature, having a minimum near 25-degrees-C, though the hydrodynamic radius of the micelles is approximately constant below 35-degrees-C. The extremely small zeta-potential at 25-degrees-C, 1.6 +/- 0.9 mV, is due to inclusion of Cl- by the rugose surfaces which seem implied by the strong interactions between crown heads and tails evident in a NOESY spectrum. At 15-degrees-C the zeta-potential increases to an expected value, 12 mV, because of exclusion of counterions from among head groups. The increase in zeta-potential with increasing temperature, to 16 mV at 35-degrees-C and 23 mV at 46-degrees-C, seems to arise from reduction of shielding efficiency due to increase in thermal motion and dehydration of head groups, which may change the distribution of charged head groups at the water-micelle interface. At 46-degrees-C the apparent increase of zeta-potential is due to the transition of micelle shape from spherical to rodlike.