Critical review of microemulsion phase behavior models: benefits, research gaps, industrial challenges, and roadmap

Over the past decades, microemulsions have become increasingly attractive for application in diverse areas of science and engineering mainly because of their high thermodynamic stability and spontaneous formation. Microemulsion systems exhibit unusually complex phase behavior that makes the prediction of their performance and properties very difficult, if not impossible. Despite the development of advanced characterization techniques, the high cost and time requirements have severely restricted their large-scale practical applications, particularly that various combinations of experimental techniques most often have to be used to synthesize and characterize microemulsions as each of them measures a different aspect of a microemulsion system. This fact emphasizes the irreplaceable role of predictive phase behavior models for saving time, energy as well as money. The inevitable need for such models is the encouraging factor to perform a systematic critical review of the available computational methods concerning microemulsions in this study with the main goal of guiding researchers through the maze of identifying research gaps, industrial challenges, and future directions. First, the available modeling approaches are categorized into six main classes. Then, studies in each category are compared in different aspects including the underlying physics, assumptions, simplicity, accuracy, applicability, and generality. Next, the advantages, limitations, and drawbacks of each of the current techniques are described to provide an outlook of constraints and opportunities for future development. Eventually, the present review critically examines the capabilities of the existing models to address challenging problems concerning microemulsions. Also, a future roadmap is proposed to help academic researchers and industrial practitioners develop an integrated modeling approach for a more realistic description of microemulsion systems. The proposed roadmap consists of the development of evidence-based protocols and screening guidelines that help users decide with confidence between the most appropriate models in each particular situation, development of an integrated modeling framework by finding the missing links between different types of models, and resolving the non-uniqueness problem by developing a purely theoretical regression-free model.