J. Chem. Chem. Eng. 6 (2012) 187-198 Formulation and Characterization of IPM/Water/Nonionic-Ionic Surfactant Microemulsions Enam Khalil * , Shorouq T. Al-Sotari and Mutasem O. Taha Department of Pharmaceutics and Pharmaceutical Technology, Faculty of Pharmacy, University of Jordan, Amman 11942, Jordan Received: November 22, 2011 / Accepted: January 05, 2012 / Published: February 25, 2012. Abstract: Microemulsions of both O/W and W/O types were formulated by using Brij76, Brij97 and Tween80 as nonionic surfactant and propanol or butanol as cosurfactant with isopropyl myristate oil and water. Low concentrations of sodium salts of hexanoic, decanoic, palmitic and stearic acids were added to the prepared microemulsions to assess their ability to enhance microemulsion stability. Solubilization capacity of microemulsions was estimated and compared with their conductivities at the same water content. Solubilization capacity for Tween80-containing microemulsions was found to be lower than that of Brij containing microemulsions. Different effects of the ionic surfactants at the maximum solubilization capacity were observed in both O/W and W/O microemulsions. Microemulsion conductivity results showed that different ionic surfactants exerted minor and comparable effects regardless to the implemented nonionic surfactant. Analysis of solubilization conductivity revealed that the presence of ionic surfactant can improve microemulsion solubilization capacity and provided that optimum physicochemical properties for both surfactants are fulfilled. These properties have direct impact at the goodness of the interfacial film. Key words: Microemulsion, solubilization capacity, conductivity, sodium salts of fatty acids. 1. Introduction Microemulsions (MEs) are homogenous, transparent, isotropic, thermodynamically stable dispersions of water and oil [1]. Microemulsions are of three types: water-in-oil (W/O), oil-in-water (O/W) or bicontinuous [2]. They might be stabilized either by single surfactant (nonionic or anionic), mixture of surfactants, or by cosurfactant/surfactant combination [3-4]. Cosurfactants have essential role in stabilization of microemulsions as they act as cosurfactants and cosolvents [5]. It is believed that cosurfactants fine-tune the surfactant hydrophile-lipophile balance HLB [6] which is also the small volume of the cosurfactant molecule to enable its fitting at the interface providing more coherent interfacial film and decreasing the interfacial tension [7]. The partitioning * Corresponding author: Enam Khalil, Prof./Ph.D., research fields: physical pharmacy, formulation of colloidal dosage forms, topical drug delivery. E-mail: ekayoub@ju.edu.jo, enamkhalil@yahoo.com. of the cosurfactant between the interface, the oily phase and a lesser extent of the aqueous phase will change the structure and the solubilization capacities of these phases [8]. For a stable microemulsion formulation, the selected surfactant and cosurfactant should have optimum physicochemical properties and they should be added at optimum ratio, which is known as the km value. Quantitative structure-property relationship (QSPR) models were developed in order to cut down the trial time required in the selection of the suitable surfactant-cosurfactant combination [9]. Microemulsions are graphically represented as stability areas in triangular phase diagrams [10], where each triangular corner designates certain component; the km value is estimated from the triangle area of microemulsion and used in the ME formulation. MEs have high solubilizing capacity for drugs of various polarities, which attracted the attention of many researchers to develop MEs based drug delivery systems [11-13]. One of the major obstacles in D DAVID PUBLISHING