Micelle formation of ethoxylated nonyl-phenols in aqueous solutions

The micelle formation of nonyl-phenols with various numbers of ethoxy groups (n_EO=10–40) was investigated in aqueous solutions and the study was focussed on the effect of temperature (293–323 K), the chain length and the inorganic electrolyte (NaCl) on the critical micelle concentration (c.m.c).The c.m.c. was determined by surface tension and interfacial tension measurements in a water/n-octane system. On the basis of the actual c.m.c. and its temperature dependence the thermodynamic functions of micelle formation (H°_m,S°_m,G°_m) were also calculated. The latter study comprised the determination of the thermodynamic function for unity ethoxy groups ((Y°_m)) as a function ofn_EO.According to the experimental results the micellar solutions are the more stable, the smaller the number of ethoxy groups in the tenside molecule and the higher the temperature as well as the electrolyte content of the system.