SOLUBILIZATION OF 1-BUTANOL IN A SODIUM DODECYL-SULFATE POLY(ETHYLENEOXIDE) SYSTEM BY NMR AND CONDUCTIVITY AT 298.1 AND 283.1 K

The effects of adding 0.1 molal 1-butanol to the aqueous SDS system at 298.1 K and the aqueous PEO-SDS system at 298.1 and 283.1 It have bee n studied. NMR NOESY experiments on the PEO-SDS-1-butanol system in D2 O were obtained. NMR self-diffusion experiments and measurements of NM R chemical shifts and specific conductivity were carried out on the sa mples, i.e. on samples with PEO and without PEG. The addition of 1-but anol to an aqueous SDS-PEO system decreases the critical aggregation c oncentration (c.a.c). Determination of the second critical concentrati on (c(2)) depends on the method of measurements, i.e. the molecular sp ecies monitored. Conductivity measurements will give c(2) as the SDS c oncentration where free micelles (micelles not bound to the polymer) a re formed. PEO selfdiffusion measurements, on the other hand, determin e c(2) as the SDS concentration where the polymer is saturated with SD S. Both the c.a.c and the c(2) decrease upon 1-butanol addition. Howev er, the c(2) value exhibits a larger decrease than the c.a.c value. Th us, the amount of polymer bound surfactant molecules decreases upon ad dition of 1-butanol. Micellar solubilization of 1-butanol starts at c. a.c., but the solubilization capacity is low until the surfactant conc entration reaches c(2). where the increase in solubilization is signif icant. Thus, solubilization data can be used to detect c(2), the conce ntration where free micelles form.