Adsorption dynamics of homogeneous polyoxypropylene-polyoxyethylene alkyl ether nonionic surfactants at the air/water interface

The dynamic surface tensions of two homogeneous polyoxyethylene (EO) alkyl ether nonionic surfactants with terminal hydroxy group (C12EOx, where C-12 is a dodecyl chain and x is the length of the EO chain; x = 6, 8) and two homogeneous polyoxypropylene-polyoxyethylene (PO-EO) alkyl ether nonionic surfactants (C12EOxPO3, where PO3 is a trioxypropylene chain inserted between the EOx and the terminal hydroxy group) were measured using the maximum bubble pressure method. The effects of EO chain length, the presence or absence of the PO3 chain, and the surfactant concentration on the maximum rates of surface-tension reduction and diffusion coefficient were investigated. The C12EO6PO3 surfactant exhibited the fastest rate of surface-tension reduction of the four systems studied, despite its complex hydrophobic-alkyl-chain/hydrophilic-EO-chain/hydrophobic-PO-chain structure that differs from that of conventional EO alkyl ether surfactants. The diffusion coefficients obtained from short and long time analyses indicate that surfactant diffusion to the subsurface is faster for the C12EOxPO3 surfactants than the C12EOx surfactants (short time data), while surfactant adsorption from the subsurface to the air/water interface is faster for the C12EOx surfactants than the C12EOxPO3 surfactants (long time data). (C) 2018 Elsevier B.V. All rights reserved.