Estudi teòric-experimental del comportament interfacial de mescles aquoses d'èster metílic a pressió atmosfèrica

In this work, a theoretical-experimental study of the density and the interfacial tension (IFT) at liquid - liquid equilibrium (LLE) for aqueous methyl ester mixtures of variable alkyl chain as a function of the temperature and the ester chain length has been carried out at atmospheric pressure. Mass density determinations were measured with a vibrating tube densimeter, whereas the interfacial tension was determinated with a spinning drop tensiometer. Additionally, the phase equilibria were studied with the Non-Random Two Liquid (NRTL) activity coefficient model, while the interfacial tension was correlated using the Simplified Square Gradient Theory (SSGT). Based on the experimental results, the mass density difference of both phases increases with temperature and molecular chain. The IFT also increases until reaching a maximum, which is related with the tie-line of the liquid - liquid equilibrium, representing a minimum of the methyl ester solubility in water. The combination of the activity coefficient NRTL model with the SSGT was found to be suitable for correlating the IFT of the mixtures as a function of the temperature. In a predictive manner, the interfacial concentration profiles of these mixtures were calculated. None of the compounds exhibit surface or adsorption activity.