Traditionally, it is believed that surfactants are a type of substance that can significantly reduce surface (interfacial) tension even at very low concentrations. With the deepening of research on surfactants, it is generally believed that any substance that can significantly change the surface (interface) properties or related and derived properties at lower concentrations can be classified as a surfactant.
Regardless of the type of surfactant, its molecular structure is composed of two parts. One end of the molecule is a hydrophobic group that is not extremely oleophilic, sometimes also known as an oleophilic group; The other end of the molecule is a polar hydrophilic hydrophilic group, sometimes also known as an oleophobic group or figuratively referred to as a hydrophilic head. Two types of molecular fragments or functional groups with completely opposite structures and properties are located at the two ends of the same molecule and connected by chemical bonds, forming an asymmetric and polar structure, thus endowing this special type of molecule with both hydrophilic and lipophilic properties, and neither overall hydrophilic nor lipophilic properties. The unique structure of surfactants is commonly referred to as the "amphiphilic structure", and surfactant molecules are therefore often referred to as "amphiphilic molecules".
Depending on the required properties and specific application scenarios, surfactants are sometimes required to have different hydrophilic and oleophilic structures and relative densities. By changing the type, proportion, and position of hydrophilic or lipophilic groups in the molecular structure, the desired hydrophilic and lipophilic balance can be achieved. After years of research and production, many types of surfactants have been derived, each of which contains numerous varieties, making it difficult to identify and select a specific variety. Therefore, it is necessary to scientifically classify thousands of surfactants in order to facilitate further research and production of new varieties, and to provide convenience for screening and applying surfactants.
Adsorption property
Positive adsorption in solution: increases wetting, emulsifying, and foaming properties;
Adsorption on solid surfaces: Single layer adsorption on non-polar solid surfaces,
Multi layer adsorption can occur on polar solid surfaces