Research Progress of Surfactant-Free Microemulsions: A Review

Surfactant is usually considered the key component to form microemulsion. surfactant-based microemulsion (SBME) can also be called traditional microemulsion. It has a wide range of applications. It has the advantages of high treatment efficiency and low energy consumption in oily sludge treatment. However, the latest research found that even without traditional surfactants, microemulsions can be synthesized through a three-phase system consisting of two immiscible liquids and one “amphiphilic solvent.” This new type of microemulsions is named “surfactant free microemulsion” (SFME). The so-called parental solvents refer to those solvents that can be completely or partially mixed with two immiscible solutions. SFME is similar to the traditional SBME in structure and properties, but SFME makes up for the shortcomings of the traditional microemulsions in many aspects. The application of advanced SFME is still in the exploratory stage, and in the future SFME may replace SBME in various treatment technologies similar to oily sludge treatment. This article reviews the latest research progress in the field of SFME, covering its phase behavior, structural characteristics, property analysis, oilfield applications, and potential application areas. In addition, the microemulsions’ system does not have to use water as the polar solution. At present, many articles have developed anhydrous surfactant-free microemulsions.