Emulsification, solubilization, and detergency behaviors of homogeneous polyoxypropylene-polyoxyethylene alkyl ether type nonionic surfactants

Abstract

The emulsification and solubilization properties and detergency behaviors were investigated using homogeneous polyoxypropylene-polyoxyethylene (PO-EO) alkyl ether type nonionic surfactants (C12EOxPO3, where x represents EO chain lengths of 6 and 8, and C12 and PO3 indicate the dodecyl chain and single trioxypropylene chain, respectively) and polyoxyethylene (EO) alkyl ether type nonionic surfactants (C12EOx, x = 6 and 8). These nonionic surfactants possess single EO and PO chain lengths without a distribution. An oil-in-water (O/W) type emulsion prepared using mixtures of nonionic surfactant C12EOxPO3 or C12EOx solutions and squalane was shown to be stable in the order of C12EO6PO3 << C12EO6 < C12EO8PO3 < C12EO8. The introduction of a PO chain to the terminal hydroxy group of the EO chain lowers the emulsion stability owing to the difficult orientation of a complex structure such as the hydrophobic alkyl chain–hydrophilic EO chain-hydrophobic PO chain at the water/oil interface. The solubilization of these nonionic surfactants was shown to be higher for stearic acid than for naphthalene as a solubilizate. The molar solubilization ratio (MSR) for naphthalene and stearic acid was the highest for C12EO6PO3 and C12EO8PO3, respectively. The removal of stearic acid from a gold substrate evaluated using a quartz crystal microbalance (detergency) was the highest for C12EO6PO3 among the four surfactants applied. Thus, no significant correlation was found among the emulsification, solubilization, and detergency behaviors ; however, a high performance for each objective was obtained by controlling both the EO chain length and the introduction of a PO chain.