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.

表面活性剂（Surfactant）通常被视为形成微乳液的核心组分。基于表面活性剂的微乳液（surfactant-based microemulsion, SBME）亦可称作传统微乳液，其应用范围广泛，在含油污泥处理领域具备处理效率高、能耗低的显著优势。然而最新研究表明，即便不使用传统表面活性剂，也可通过由两种不互溶液体与一种"两亲性溶剂（amphiphilic solvent）"构成的三相体系合成微乳液。这类新型微乳液被命名为"无表面活性剂微乳液（surfactant-free microemulsion, SFME）"。所谓双亲溶剂，指的是可与两种不互溶溶液完全或部分混溶的溶剂。SFME在结构与性能上与传统SBME高度相似，但在诸多方面弥补了传统微乳液的不足。当前先进SFME的应用仍处于探索阶段，未来其或可在含油污泥处理等各类处理技术中取代SBME。本文综述了SFME领域的最新研究进展，涵盖其相行为、结构特征、性能分析、油田应用及潜在应用领域。此外，微乳液体系并非必须以水作为极性溶剂，目前已有多篇文献开发出无水无表面活性剂微乳液。