The effect of polyethylene glycols on the interaction and stability of AOT/water/isooctane microemulsions

The influence of water-soluble polyethylene glycols PEG200 on the properties of sodium bis(2-ethylhexyl)-sulfosuccinate (AOT) water-in-isooctane microemulsions has been investigated by conductivity measurement and isothermal titration microcalorimetry (ITC). The percolation temperatures (T-p) the thermodynamic properties of droplet aggregation and the interaction enthalpy (-Delta H-phi) between droplets for AOT/water/PEG200/isooctane with different PEG concentrations and a fixed molar ratio of water to surfactant omega = 22.2 were determined. Based on a two-stage thermodynamic approach of the percolation, we obtained the fusion enthalpy (Delta H-f(0)) of the close contact droplets by a combination of the droplet aggregation enthalpy (Delta H-ag(0)) and -Delta H-phi. It was found that both (-Delta H-phi) and (-Delta H-f(0)) varied with the concentration of PEG200 (c(PEG)) and had the extreme value at c(PEG) = 25 gL(-1). This phenomenon was interpreted by the variation of interface rigidity due to the varied distributions of added PEG200 between the water pool and the surfactant interface. (C) 2018 Production and hosting by Elsevier B.V. on behalf of King Saud University.