Nonionic surface-active agents. Part IV. The critical micelle concentration of some polyoxyethylene glycol monohexyl ethers in binary and ternary systems

Abstract

The critical micelle concentration (c.m.c.) of some relatively pure nonionic ethers of structure C 6H 13(O·CH 2·CH 2) n OH ( n = 2 to 6), prepared by a synthetic method presviously described, have been studied in binary systems containing the surface-active agents in aqueous solution, and in ternary systems in the presence of benzene, n-octanol, or 4-chloro-3, 5-xylenol. In each case the c.m.c. was found to be in the range 0.05–0.1 M, the strong interaction between phenols and nonionic surface-active agents apparently having little effect on the value. Support is thus given to the suggestion that large shifts in the c.m.c. of surface-active agents in the presence of solubilized materials occur only where ionic effects are important. Below the c.m.c. of one of the above polyethers ( n = 6), the solubility of the additives was less than their solubility in water, and in the case of the phenol there was in addition a change in the nature of the phase or phases in equilibrium with the aqueous phase in systems containing more than about 0.5% of the surface-active agent. The possibility of confusing the c.m.c. with a phase change when sharp changes in certain properties are used as an indication of the c.m.c. and where no check is made of the phases present, is thus apparent. It seems possible that certain breaks in conductivity and solubility curves which have been reported might be explained on this basis.