| Abstract: | 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 K have been studied. NMR NOESY experiments on the PEO– SDS–1-butanol system in D2O were obtained. NMR self-diffusion experiments and measurements of NMR chemical shifts and specific conductivity were carried
out on the samples, i.e. on samples with PEO and without PEO. The addition of 1-butanol to an aqueous SDS–PEO system decreases
the critical aggregation concentration (c.a.c). Determination of the second critical concentration (c
2) depends on the method of measurements, i.e. the molecular species monitored. Conductivity measurements will give c
2 as the SDS concentration where free micelles (micelles not bound to the polymer) are formed. PEO self-diffusion measurements,
on the other hand, determine c
2 as the SDS concentration where the polymer is saturated with SDS. Both the c.a.c and the c
2 decrease upon 1-butanol addition. However, the c
2 value exhibits a larger decrease than the c.a.c value. Thus, the amount of polymer bound surfactant molecules decreases upon
addition of 1-butanol. Micellar solubilization of 1-butanol starts at c.a.c., but the solubilization capacity is low until
the surfactant concentration reaches c
2, where the increase in solubilization is significant. Thus, solubilization data can be used to detect c
2, the concentration where free micelles form.
Received: 21 July 1997 Accepted: 9 February 1998 |
