Surface forces in wetting, flotation and capillary phenomena

Abstract

Surface forces play a crucial role in disperse systems, containing colloidal particles or thin films. Theory of wetting, based on the Frumkin-Derjaguin approach, relates the contact angles with isotherms of disjoining pressure Π(h) of wetting films. On the basis of the isotherms obtained, contact angles were calculated and compared with experimental data. It was shown that in the region of contact angles from 10 to 50 degrees it is sufficient in some cases to take into account the molecular and electrostatic forces only. Complete wetting is guaranteed by the action of hydrophilic repulsion forces, whereas large contact angles arise under the action of hydrophobic attraction forces. The effects of surfactants on contact angles’ formation, wetting films’ stability and flotation are discussed. Capillary phenomena, influencing kinetics of penetration and mutual displacement of fluids were investigated using model systems. The kinetics is crucially influenced by addition of surfactants. Capillary pressure of a moving meniscus changes as a result of a mass exchange of surfactant molecules between the meniscus, solid wall and forming film interfaces. The arising effects were investigated in dependence on flow rates, electrolyte and surfactant concentration.