Surfactant is a kind of organic compounds with a long history and many kinds [1,2]. Traditional surfactants contain both hydrophilic and hydrophobic components in their molecular structure, and thus have the ability to reduce the surface tension of water - hence their name. In the subject classification, surfactants belong to the research category of colloid and interface chemistry under physical chemistry. At the same time, it has inextricably linked with other disciplines. For example, surfactants can spontaneously form highly ordered supramolecular structures in solution, contrary to the law of entropy increase in thermodynamics; Various self-assembled structures that fall within the scope of nanoscience and can be used as templates for the synthesis of other nanomaterials; The vesicles in the self-assembly structure, similar to the structure of the cell membrane, can be used as a vehicle for drug delivery, and so on. These characteristics make the study of surfactants flourishing and enduring. The development of the chemical industry and the improvement of organic synthesis technology have promoted the continuous innovation of surfactants. Therefore, it can be said that surfactant science is an old and young knowledge, and it continues to surprise us today
People's understanding of surfactants mostly originates from various washing products. Indeed, washing is the oldest and still well known function of surfactants. But in fact, the story of surfactants is much longer than we think, and even more closely related to the activities and origins of life. Surfactants have been with us since the birth of life, and they exist naturally in human body and animals and plants, including phospholipids, the skeleton of cell membrane, alveolar surface active substances, bile acids, which play an important role in fat metabolism. In recent years, with more and more support for the theory that life originated from deep-sea hot vents, the important role of surfactants in the origin of life is being paid attention to. It is increasingly believed that phospholipids provided the basic conditions for the first life to escape the pores of rocks [3]. Subsequently, surface active proteins, cholic acids and other members successively join the regulatory path of life activities, building a colorful and dynamic world.
The surfactants used in the early days - mainly soaps and detergents - were also often derived from organisms [4,5]. About 5,000 years ago, the ancient Egyptians found that the carbon ash of sheep oil can be used as a detergent, and China's ancient saponin, "bath bean" (commonly known as pancreas) and Turkey red oil in Europe are classic cases of the use of surfactants by ancient humans. With the development of The Times, these natural surfactants have been unable to adapt to the needs of industrial and agricultural production and People's Daily life. Thanks to the development of synthetic chemistry and the progress of chemical processes, a variety of surfactants have been developed, their structures have changed greatly, and some new concepts have been developed.
Despite the achievements of surfactant science, there are still some shortcomings. The discovery of new surfactants has expanded the types of surfactants, but there is still a long way to go how to correctly select them in combination with specific application scenarios. The types of hydrophilic and hydrophobic groups contained in many surfactants with novel structures are still very limited, and need to be further expanded, and their preparation routes still need to be optimized to reduce costs. It also takes time to fully understand the properties of many new surfactants.
The use of surfactants also presents some challenges. With the increasing of people's awareness of environmental protection, the environmental compatibility and biocompatibility of surfactants have become a topic of concern. Although fluorocarbon surfactant has unique properties, it is easy to retain in human body, so its application is limited to some extent. The degradation products of alkylphenol polyoxyethylene ethers have also been found to be potentially harmful to humans. A large amount of phosphorus-containing surfactants can easily cause excessive growth of aquatic plants, thus interfering with the normal life of aquatic animals. After the cationic surfactant strays into the human body, it is easy to combine with the phosphoric acid in the cell membrane, thus interfering with the normal function of the cell. Therefore, the development of environmental and biofriendly surfactants is an important research direction in this field. Natural (biomass) surfactants have high hopes in this regard. Surfactants come from nature and will return to nature.
