Characterization of Microemulsions Prepared using Isopropyl Palmitate with various Surfactants and Cosurfactants

Purpose: To investigate the effect of various surfactants and\ncosurfactants, and their ratio on microemulsions prepared with\nisopropyl palmitate (IPP) Methods: Tween 20, 40, 60, and 80 were used\nseparately as surfactant with methanol, ethanol, 1-propanol, 1-butanol\nor 1-pentanol as cosurfactant, and IPP as oil phase to prepare various\nmicroemulsions. Various surfactant to cosurfactant ratios (1:1, 2:1,\n3:1, 4:1, and 1:0) were used in the preparation. Pseudoternary phase\ndiagram was used to define the microemulsion area, and samples from the\nbest combinations, i.e., those that produced the largest volume of\nmicroemulsion, were subjected to further characterization by polarized\nlight microscopy, differential scanning calorimetry (DSC), zetasizer,\nrheometer, and for stability. Results: Based on the microemulsion areas\nproduced in the pseudoternary phase diagrams, the the surfactants were\nranked in the following order of effectiveness: Tween 80 > 60 >\n40 > 20 while the alcohols (co-surfactants) were ranked as follows:\n1-butanol > 1-pentanol > 1-propanol > ethanol = methanol. The\nbest surfactant to cosurfactant ratio for microemulsion preparation was\n3:1. Conclusion: The selected surfactant/co-surfactant combination\n(i.e., Tween 80:1-butanol, 3:1) produces a stable microemulsion\npossesses a good potential as a drug delivery system.