Characterization of microemulsion structures in the pseudoternary phase diagram of isopropyl palmitate/water/Brij 97 : 1-butanol

This research was aimed to characterize microemulsion systems of isopropyl palmitate ( IPP), water, and 2: 1 Brij 97 and 1-butanol by different experimental techniques. A pseudoternary phase diagram was constructed using water titration method. At 45% wt/wt surfactant system, microemulsions containing various ratios of water and IPP were prepared and identified by electrical conductivity, viscosity, differential scanning calorimetry ( DSC), cryo-field emission scanning electron microscopy ( cryo-FESEM) and nuclear magnetic resonance ( NMR). The results from conductivity and viscosity suggested a percolation transition from water-in-oil ( water/oil) to oil-in-water ( oil/water) microemulsions at 30% wt/wt water. From DSC results, the exothermic peak of water and the endothermic peak of IPP indicated that the transition of water/oil to oil/water microemulsions occurred at 30% wt/wt water. Cryo-FESEM photomicrographs revealed globular structures of microemulsions at higher than 15% wt/wt water. In addition, self-diffusion coefficients determined by NMR reflected that the diffusability of water increased at higher than 35% wt/wt water, while that of IPP was in reverse. Therefore, the results from all techniques are in good agreement and indicate that the water/oil and oil/water transition point occurred in the range of 30% to 35% wt/wt water.