Short-Chain Diol Effects on the Self-Assembly of Polyoxyethylene Oleyl Ethers in Dilute Aqueous Solutions and Their...

In the present work, the effect of 1,2-propylene glycol (1,2-PG) or 1,3-butylene glycol (1,3-BG) incorporation on the self-assembling behaviors of polyoxyethylene oleyl ethers in dilute aqueous solutions is extensively investigated. This study aims to elucidate the mechanism by which the short-chain diol introduction contributes to preventing the phase separation occurring in aqueous makeup cleansing products under high temperatures. The critical micellization concentration and standard free energy of micellization of polyoxyethylene oleyl ethers in 1,2-PG-water mixed solvents steadily increase with increasing concentration of 1,2-PG in water, indicating that the addition to water of 1,2-PG disfavors micelle formation. Additionally, the introduction of 1,2-PG resulted in a significant increase in the effective surface area demand per molecule of polyoxyethylene oleyl ether, pointing to a reduction in the packing tightness of the surfactant molecules. Results of SAXS experiments indirectly demonstrate that the effective critical packing parameter of polyoxyethylene oleyl ethers in the aqueous solution of 1,2-PG decreases with increasing 1,2-PG concentration, which corresponds well with the changes in the cloud point of amphiphiles. NMR measurements confirm that these observations may be related to the swelling of the hydrophilic chain induced by excessive water penetration into the palisade layer, which helps counteract the dehydration of the POE (polyoxyethylene) segments induced by elevated temperatures. Furthermore, 1,3-BG exhibits effects similar to those of 1,2-PG but with a notably stronger intensity.