Adsorption and aggregation properties of alkoxy-group-modified homogeneous polyoxyethylene alkyl ether nonionic surfactants

Abstract The development of new surfactants with interesting properties and new functionalities that can be controlled in a simple manner is an important industrial objective. Herein, we report the synthesis of homogeneous polyoxyethylene (EO) alkyl ether nonionic surfactants modified with alkoxy groups (C 12 EO 8 OR, where C 12 and EO 8 are dodecyl and octaoxyethylene chains, respectively, and R = Me and Et) from a homogeneous EO-type hexaoxyethylene dodecyl ether (C 12 EO 6 ) and diethylene glycol monomethyl ether or diethylene glycol monoethyl ether. The adsorption and aggregation properties of these surfactants were characterized through cloud point and surface tension measurements, and by small-angle X-ray scattering, polarization microscopy, and cryogenic transmission electron microscopy; these properties were compared to those of previously reported homogeneous EO-type (C 12 EO 8 ) and polyoxypropylene-polyoxyethylene type surfactants (C 12 EO 8 PO y , y  = 1, 2, 3). The introduction of a methoxy or ethoxy group at the terminus of the EO chain in C 12 EO 8 resulted in an increase in hydrophobicity and a greatly reduced cloud point. Substitution of the terminal hydroxy group of the EO chain in C 12 EO 8 with methoxy and then ethoxy led to increasingly lower surface tensions in solution and more efficient air/water interfacial adsorption. C 12 EO 8 OR formed small micelles at low concentrations in solution, and the micelles of C 12 EO 8 OMe transformed to hexagonal liquid crystals with increasing surfactant concentration, whereas C 12 EO 8 OEt remained to form micelles even at high concentration; that is, the introduction of bulkier functional groups into the C 12 EO 8 surfactant helps to control the formation of aggregates with higher-order structures.