Adsorption behavior of non-conventional eco-friendly tyrosine glycerol ether surfactants

Due to the increasing demand for environmentally friendly surfactants, a novel non-conventional glycerol ether surfactant with 12 carbon atoms in the hydrophobic alkyl chain and the amino acid tyrosine in the hydrophilic head (TyrGE12) is synthesized. Measurements of dynamic surface tension by maximum bubble pressure tensiometry and drop profile tensiometry are carried out for alkali aqueous solutions over a wide concentration range and for surface ages spanning from milliseconds to hours. Critical Micelle Concentration (CMC) value, standard free energy of adsorption and other physicochemical properties are calculated based on static (equilibrium) surface tension measurements. Dynamic surface tension data are analyzed using approximate solutions of the Ward and Tordai model to estimate diffusion coefficients for short and long adsorption times. For concentrations above the CMC, the effective diffusion coefficient (D*) of monomers is also estimated. Diffusion coefficients for short adsorption times lie in a physically reasonable range whereas for long adsorption times the computed very low values indicate the presence of an adsorption barrier. Interfacial dilatational storage modulus and loss modulus measurements indicate a dominant elastic character of the adsorption layer for all the examined concentrations and oscillation frequencies. Local peaks in the values of both moduli, below and above CMC, imply that structural changes in the adsorption layer might be partially affected by the presence of micelles.