English abstract
This study investigates the surfactant-surfactant interaction in anionicnonionic mixed micelles. Surfactants selected in this work consist of anionic sodium dodecyl sulfate (SDS); a CS series of lauryl ether sulfates (C$130, CS230, CS330) having different degree of ethoxylation, and a toctylphenoxypolyethoxyethanol (Triton X-100). The critical micelle concentrations in single surfactant systems were determined by surface tension, conductivity and fluorescence measurements and were found to be 0.8 mm, 8.3 mM and 0.22 mM for CS series, SDS and Triton X-100 respectively. The values obtained by the three different measurements are in close agreement and were close to the reported ones in the literature. The lower CMC of the lauryl ether sulfates compared to SDS was associated to the intramolecular ion-dipole interaction in lauryl ether sulfate surfactants. The CMCs of CS series were found to be similar, indicating that only the introduction of one ethylene oxide (EO) group is responsible for the substantial decrease in the CMC from 8.3 mM (SDS) to 0.8 mM (C$130). Interestingly, the ionization degree Bion (0.75 F 0.05) in lauryl ether sulfates were similar and higher that the degree of ionization in SDS micelles (0.35 F 0.03), suggesting that the charge density in SO4 (in CS series) is higher than the charge density in SDS sulfate group.
Surfactant-surfactant interaction was investigated in ethoxylated /TX-100 mixed micelles system (CS130/TX-100, CS230/TX-100, and CS230/TX-100) and in nonethoxylated sulfate/Triton X-100 (SDS/TX-100) as well in order to compare the relative strengths of interaction between those two systems. In all surfactant mixtures CS-series/TX-100 and SDS/TX-100, the experimental CMCs were lower than the ideal ones. This negative deviation from ideality is reflecting synergism. Surfactant-surfactant interaction parameters in mixed micelles su were derived according to Rubing's theory. The higher BM value (- 3.7) in SDS/TX-100 system indicates a strong interaction between SDS and TX-100, whereas relatively weaker interaction was found between CS series and TX-100 as reflected by the relatively lower BM value (-1.38) found in these systems. This was attributed to the intramolecular ion-dipole interaction in ethoxylated sulfated surfactants both in single surfactant micelles as well as in CS/TX-100 mixed micelles.
