Water solubilization capacity and conductance behaviors of AOT and NaDEHP systems in the presence of additives

Abstract

The influences of two typical additives, long-chain organic molecule (bis(2-ethylhexyl) phosphoric acid (HDEHP)) and inorganic electrolyte (sodium chloride), on the water solubilization capacity of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and sodium bis(2-ethylhexyl) phosphate (NaDEHP) in n-heptane solutions have been investigated. The presence of optimal content of HDEHP remarkably enhances the water solubilization capability of the NaDEHP system, while it decreases the solubilization capacity of the AOT system. The addition of low concentration of NaCl solution in the AOT microemulsions tends to enhance its solubilization capacity. The conductance behaviors of the AOT system have also been investigated, focusing on the influences of the HDEHP content, NaCl concentration, and temperature. For the water/AOT/ n-heptane reverse micelles/microemulsions, with increasing water content, no percolation phenomena can be observed in the presence of HDEHP; whereas the percolation conductance occurs with the addition of NaCl solutions and the onset water content increases with an increase of the NaCl concentration. With an increase of temperature, the percolation conductance also occurs in the AOT system in the presence of HDEHP and the onset temperature for the percolation conductance decreases with increasing HDEHP content. The influences of the variables on the water solubilization capacity and conductance behaviors could be understood from their effects on the rigidity of the oil/water interface and the attractive interactions of the surfactant aggregates.