Dynamic surface properties of eco-friendly phenylalanine glycerol ether surfactants at the W/A interface

Abstract

Dynamic surface tension and dilatational viscoelasticity data are presented for aqueous solutions of novel nonconventional eco-friendly phenylalanine glycerol ether surfactants, with 12 carbon atoms in the hydrophobic alkyl chain, PhGE12. Adsorption kinetics is studied in a broad range of concentrations and for time scales spanning from several milliseconds to several hours employing maximum bubble pressure tensiometry and drop profile tensiometry. Standard free energy of adsorption and diffusion coefficients for both short and long adsorption times are calculated and discussed. For short adsorption times diffusion coefficients lie in a physically reasonable range but for long adsorption times extremely low values are computed indicating the presence of an adsorption barrier. This barrier appears to mask any micellar kinetics effect for long adsorption times. Measurements of interfacial dilatational storage modulus and loss modulus indicate a visco-elastic character of the adsorption layer for all the examined concentrations and oscillation frequencies. Local peaks in the values of both moduli imply that structural changes occur with increasing concentration. However, these changes seem to be unrelated to the presence of micelles since they are observed at concentrations below the CMC.