Abstract:

Foams are widely used in many fields, such as food, cosmetics, medicine, and mineral flotation. The addition of inorganic salts to ionic surfactants will affect the adsorption of surfactants at the air-liquid interface and the solubility of surfactants in solution, thus influencing the evolution of foams. At present, the influences of salts on the evolution of foams of ionic surfactants are still not clear. In this work, the influence of potassium chloride （KCl） on the evolution of foam of sodium dodecyl sulfate （SDS） in the low concentration range was systematically studied. It was found that, when the concentrations of salt and surfactant were both low, the stability of the foam prepared was similar to that without salt, in which the foam was stabilized by surfactant molecules; when the concentrations of salt and surfactant were both increased and their concentrations were close to each other, the salt promoted the adsorption and crystallization of surfactant molecules at the air-liquid interface due to electrostatic interaction, making the stability of foam better than that of pure surfactant, in which the foam was stabilized by inorganic-salt enhanced surfactant molecules; when the salt concentration was slightly higher than the surfactant concentration, the surfactant crystal particles adsorbed on the network of foam, and the local crystals destroyed the liquid film of foam, thus making the foam unstable, in which the foam was stabilized by surfactant molecules under the interference of surfactant crystals; when the salt concentration was further increased, the surfactant crystal particles completely covered on the air-liquid interface of foam, and ultra-stable Pickering foam was obtained by forming solid particle barrier. This research work might have important theoretical guiding significance for further exploring the evolution theory of foams stabilized by surfactant crystal particles and their applications in related fields.

Key words: salt effect, SDS, foam evolution, surfactant crystal