The adsorption of interfacial active molecules on oil-water interface will directly affect its interfacial properties

such as interfacial tension

interfacial dilatational rheology

which influences the stability of oil/water emulsions.The interfacial properties could be quantitatively analyzed by introducing a proper adsorption model.In this work

Span 80 was selected as the surface active component and added in a mineral oil-deionized water system.The interfacial tension and dilatational rheology were measured below and above the critical micelle concentration(CMC

0.45 mmol·L-1 in this work).It was found that the interfacial dilatational modulus increased first and then decreased as the concentration of Span 80 continued to increase.Since the pure diffusion controlled model was insufficient to accurately describe the relaxation behavior

the relaxation model from Lucassen-van den Tempel was combined with dynamic adsorption models

such as Langmuir

Frumkin

reorientation

and rigorous reorientation model.The results showed that a combination with rigorous reorientation model accurately predicted the oil/water interfacial tension and indicated the influence of surfactant

frequency on interfacial dilatational modulus properly. Interfacial tension and dilatational modulus were measured with the spinning drop method.During the measurement

an oil drop of 2.5 μl was injected into the capillary filled with deionized water.The capillary was rotated at 10000 r·min-1

and the temperature was maintained with an air bath circulation system.The image profile of the droplet was recorded with a video camera at 4 fps.Interfacial tension was calculated from the geometric contour of the drop with the Young-Laplace equation

while interfacial dilatational modulus was determined from the difference of interfacial tension and interfacial area. Interfacial dilatational modulus was determined after equilibrium adsorption of Span 80 molecules.