Surfactant refers to a substance that has fixed hydrophilic and lipophilic groups, can be aligned on the surface of the solution, and can significantly reduce the surface tension. Hydrophilic groups are often polar groups, such as carboxylic acid, sulfonic acid, sulfuric acid, amino or amine groups and their salts, or hydroxyl, amide groups, ether bonds, etc.; and hydrophobic groups are often non-polar Hydrocarbon chains, such as hydrocarbon chains with more than 8 carbon atoms. Surfactants are divided into ionic surfactants and nonionic surfactants.
The molecular structure of surfactants is amphiphilic: one end is a hydrophilic group and the other end is a hydrophobic group.
Through the affinity of different parts of the molecule to the two phases, both phases regard it as a component of the original phase, and the molecules are arranged between the two phases, so that the surface of the two phases is equivalent to turning into the interior of the molecule. thereby reducing surface tension. Since the two phases regard it as a component of the original phase, it is equivalent to the fact that the two phases and the surfactant molecules do not form an interface, which is equivalent to partially eliminating the interface of the two phases in this way, which reduces the surface tension and surface free energy.
Positive adsorption in natural cationic surfactants solution: increase wettability, emulsification, and foaming; adsorption on solid surface: single-layer adsorption on non-polar solid surface, and multi-layer adsorption on polar solid surface.
Natural cationic surfactants can reduce the surface tension of water by adsorbing at the gas-liquid two-phase interface, and can also reduce the interfacial tension of oil and water by adsorbing at the liquid interface. Many surfactants can also aggregate into aggregates in bulk solution. Both vesicles and micelles are such aggregates. The concentration at which a surfactant begins to form micelles is called the critical micelle concentration or CMC. When micelles are formed in water, the tails of the micelles form a core that wraps around the oil droplet, while their (ionic/polar) heads form a shell that remains in contact with the water.
Surfactants aggregate in oil and the aggregates are referred to as reverse micelles. In reverse micelles, the head is at the nucleus and the tail remains in full contact with the oil. Surfactants are generally divided into four main groups: anionic, cationic, nonionic, and zwitterionic (two-electron). The thermodynamics of surfactant systems are important, both theoretically and practically. Because surfactant systems represent systems between ordered and disordered states of matter. Surfactant solutions may contain ordered and disordered phases.