The dilute solution of surfactant obeys the rule of ideal solution. The amount of surfactant adsorbed on the surface of the solution increases with the increase of the concentration of the solution. When the concentration reaches or exceeds a certain value, the amount of adsorbed surfactant no longer increases. These excessive surfactant molecules are disorderly or exist in a regular way in the solution. Practice and theory show that they form associations in solution, which are called micelles.
Surface Pressure of Adsorption Membrane: Surfactant adsorbs at the gas-liquid interface to form an adsorptive film. For example, a frictionless movable floating sheet is placed on the interface to push the adsorptive plasma membrane along the solution surface. The membrane produces pressure on the floating sheet. This pressure is called surface pressure. Surface Viscosity: Like surface pressure, surface viscosity is a property of insoluble molecular membranes.
Suspension of a white gold ring with fine metal wire, so that its surface contact with the water surface of the sink, rotate the white gold ring, and the white gold ring is hindered by the viscosity of the water, and the amplitude gradually decays. Based on this, the surface viscosity can be measured. The method is: first, carry out the experiment on the pure water surface, measure the amplitude attenuation, then determine the attenuation after forming the surface film, and obtain the viscosity of the surface film from the difference between the two.
The surface viscosity is closely related to the firmness of the surface film. Because the membrane has surface pressure and viscosity, it must be elastic. The higher the surface pressure and the higher the viscosity of the adsorbed film, the greater the elastic modulus of the adsorbed film. The modulus of elasticity of the surface adsorption film plays an important role in foam stabilization.
Surfactant is a major component of detergent decontamination formula. In addition to special uses, these products are discharged into the environment directly or after treatment by sewage treatment plants. However, anionic surfactants, which are difficult to biodegrade, are the main detergents. The discharge of surfactant-containing wastewater not only directly endangers the aquatic environment, kills microorganisms in the environment and inhibits the degradation of other toxic substances, but also leads to the reduction of dissolved oxygen in water, especially the eutrophication of water caused by surfactants containing nitrogen and phosphorus. When the concentration of surfactant in sewage of sewage treatment plant reaches a certain level, it will affect many processes such as aeration, sedimentation, sludge nitrification and so on.