Temperature effect on the adsorption and micelle formation of pentaethylene glycol monoalkyl ethers

The temperature effect on the adsorption at air/water interface and micelle formation of poly(ethylene glycol) monoalkyl ether (C_iE_j) nonionic surfactant was investigated on the basis of the thermodynamic strategy. From the results of surface tension experiments and after applying the thermodynamic treatment, surface density and thermodynamic quantity changes associated with the adsorption and micelle formation were obtained. It has been found that the entropy of adsorption from monomeric state of C_iE_j is positive and depend on both concentration and temperature in the same trend; the entropy increases with increasing adsorption of surfactant and increasing temperature. This phenomenon is against that of ionic surfactant. The difference was analyzed in term of the competition between the dehydration effect and the orientation effect. For C_iE_j nonionic surfactant systems, the large amount of dehydration at high temperature dominates the controversial results of surface density and entropy changes. Moreover, the effect of hydrophobic chain length on the surface adsorption and micelle formation was included in this study using three C_iE₅'s with i = 8, 10, and 12. Those gave outstanding aspects with respect to the thermodynamic property changes.