SurfactantsThe molecule has a lipophilic group and a hydrophilic group, which is an amphiphilic molecule. Water is a highly polar liquid, when the surfactant is dissolved in water, according to the principle of polar similarity and polarity repulsion, its hydrophilic group is attracted to water and dissolved in water, and its lipophilic group is repelled by water and leaves water, and as a result, surfactant molecules (or ions) are adsorbed on the interface of the two phases, so that the interfacial tension between the two phases is reduced. The more surfactant molecules (or ions) adsorb at the interface, the greater the reduction in interfacial tension.
Surface pressure of adsorption membrane: The surfactant is adsorbed at the gas-liquid interface to form an adsorption film, such as placing a frictionless movable float on the interface, and pushing the adsorbent membrane along the surface of the solution with the float, the membrane produces a pressure on the float, which is called surface pressure.
Surface viscosity: Like surface pressure, surface viscosity is a property exhibited by insoluble molecular films. Suspend a platinum ring with a thin metal wire, so that its plane touches the water surface of the sink, rotate the platinum ring, the platinum ring is hindered by the viscosity of water, and the amplitude gradually decays, according to which the surface viscosity can be determined, the method is: first carry out experiments on the surface of pure water, measure the amplitude attenuation, and then measure the attenuation after the formation of the table, and obtain the viscosity of the table ** from the difference between the two.
The surface viscosity is closely related to the firmness of the table.
Since the adsorbent film has surface pressure and viscosity, it must be elastic. The greater the surface pressure and the higher the viscosity of the adsorbed membrane, the greater its elastic modulus. The elastic modulus of the surface adsorption film is of great significance in the foam stabilization process.
The dilute solution of the surfactant obeys the law followed by the ideal solution. The adsorption capacity of surfactant on the surface of the solution increases with the increase of the concentration of the solution, and when the concentration reaches or exceeds a certain value, the adsorption capacity does not increase, and these excessive surfactant molecules are disorderly in the solution, or exist in some regular way. Both practice and theory show that they form associations within solution, which are called micelles.