What is a surfactant
Surfactants are a class of amphiphilic molecules that include a hydrophilic polar portion and a hydrophobic non-polar portion. The non-polar portion is usually a hydrophobic alkyl chain. The polar hydrophilic group enables the surfactant to be dissolved in water as a monomer. However, when the surfactant in the aqueous solution reaches a certain concentration, the monomer surfactant forms a spherical structure with the hydrophilic groups facing outward and the hydrophobic groups facing in through the hydrophobic interaction of the alkyl chain. This structure is called The concentration of micelles that allows surfactants to form micelles in a solution is called the critical micelle concentration (CMC).
The single surfactant concentration reached the critical micelle concentration, and the monomer surfactant concentration in the solution no longer increased, and micelles formed spontaneously. Although micelles are often reduced to symmetrical spheres, the micelles in solution actually make a dynamic, extremely irregular shape. The critical micelle concentration is one of the most important properties of surfactants, and has an important effect on protein-surfactant interactions. Generally, the monomer surfactant and the micelle-forming surfactant The interactions are vastly different. It is worth noting that the critical micelle concentration of the surfactant is related to the ionic strength of the buffer. Ions in the solution reduce the electrostatic repulsion of the surfactant, which reduces the critical micelle concentration. For example, the critical micelle concentration of commonly used SDS anionic surfactants in aqueous solutions is 7 to 8 mM, but 0.8 to 1 mM in PBS buffer. In addition, the formation of free micelles is also related to the protein in the solution. When the protein is present in the solution, it will interact with the surfactant in the solution, reducing the concentration of free monomer surfactants, thereby increasing the surfactant's Critical micelle concentration.