Purpose: To investigate the effect of various surfactants and cosurfactants, and their ratio on microemulsions prepared with isopropyl palmitate (IPP)

Methods: Tween 20, 40, 60, and 80 were used separately as surfactant with methanol, ethanol, 1-propanol, 1-butanol or 1-pentanol as cosurfactant, and IPP as oil phase to prepare various microemulsions. Various surfactant to cosurfactant ratios (1:1, 2:1, 3:1, 4:1, and 1:0) were used in the preparation. Pseudoternary phase diagram was used to define the microemulsion area, and samples from the best combinations, i.e., those that produced the largest volume of microemulsion, were subjected to further characterization by polarized light microscopy, differential scanning calorimetry (DSC), zetasizer, rheometer, and for stability.

Results: Based on the microemulsion areas produced in the pseudoternary phase diagrams, the the surfactants were ranked in the following order of effectiveness: Tween 80 > 60 > 40 > 20 while the alcohols (co-surfactants) were ranked as follows: 1-butanol > 1-pentanol > 1-propanol > ethanol = methanol. The best surfactant to cosurfactant ratio for microemulsion preparation was 3:1.

Conclusion: The selected surfactant/co-surfactant combination (i.e., Tween 80:1-butanol, 3:1) produces a stable microemulsion possesses a good potential as a drug delivery system