A thermodynamic study on the surface tension of amines and glycol ethers and their solutions with water

A surface tension model for dilute aqueous systems that could be used to quickly screen the behavior of many organic compounds was sought. A simple molecular thermodynamic based model of Lu et al. was identified and chosen. The model is composed of three additive terms that contribute to the surface tension: a hard sphere repulsive-repulsive term, a dispersive interaction term, and a polar interaction term. The model has two adjustable parameters, size and energy, which were obtained by optimization of an objective function for each pure fluid. Amines and glycol ethers were selected as test compounds since they present opportunities for use as shrinkage reducing admixtures (SRA) in concrete, a commercially important surface tension related application. When the model uses only the pure component parameters to predict the aqueous mixture surface tension, the resulting predictions are not good. Two binary interaction parameters were required in order to correlate the mixture data well. An attempt was also made to use average binary interaction parameters to predict the surface tension of dilute aqueous systems for compounds in various classes but this approach proved to be ineffective. A number of conjectures, however, regarding the relationships between molecular structure and behavior of the dilute surface tension-composition slope were identified. Additional compounds were selected in order to fully evaluate each conjecture and the surface tension of those aqueous mixtures was measured experimentally. The experimental results support the structure-property conjectures identified.