Studies on the Micellar Behaviour of Binary Surfactant Systems: Sodium Oleate + Alcohol Oxyethylates

The critical micelle concentration of binary surfactant systems containing sodium and four commeicial alcohol ethoxylates [CH₃ (CH₂)_n o (-CH₂ CH o-)_mH], of comparable HLB values has been determined by surface tension and spectral change methods. The results have been used to examine the micellar behaviour of the binary surfactant systems. It has been observed that alcohol ethoxylate with small hydrophopic chain (i.e. average n=9 and m=6) is compatible with sodium oleate to form mixed micelles. Surfactant systems containing relatively higher hydrophobic chain length (i.e. average n = 12.5 to 14 and m = 6.5 to 7.0) were found to exhibit non-ideal mixing behaviour resulting into a pseudo-phase separation in non-ionic rich and anionic rich micelles. The synergistic properties of the binary surfactant systems were found to be highly sensitive to the hydrophobic chain length of the non-ionic surfactant.