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

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

AAPS PharmSciTech (2006-06-27)
Prapaporn Boonme, Karen Krauel, Anja Graf, Thomas Rades, Varaporn Buraphacheep Junyaprasert
ABSTRACT

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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
BRIJ® O20, average Mn ~1,150
Supelco
Isopropyl palmitate, Pharmaceutical Secondary Standard; Certified Reference Material
Sigma-Aldrich
ECO BRIJ® O10
Sigma-Aldrich
ECO BRIJ® O20, average Mn ~1,150
Sigma-Aldrich
Brij® 93, average Mn ~357
Sigma-Aldrich
Isopropyl palmitate, technical grade, 90%
Sigma-Aldrich
Isopropyl palmitate, ≥90%
Sigma-Aldrich
Brij® O10