结合吸附模型预测油水液滴的界面流变性质

Interfacial rheological properties of oil/water droplet with dynamic adsorption models

界面活性分子在油水界面的吸附将改变其界面性质,如界面张力、界面流变性质,从而影响乳状液体系的稳定。通过吸附模型较为准确地描述活性分子在界面上的吸附行为,是定量描述油水界面性质的有效方法之一。以Span80为界面活性物质,模拟油、去离子水为实验介质,研究了低于及超过临界胶束浓度(实验中确定为0.45mmol.L-1)下界面张力及界面扩张模量的影响特性,表现为界面扩张模量随Span浓度的增加而先增大后减小的趋势。将描述纯扩散弛豫的Lucassen-van den Tempel模型,同Langmuir、Frumkin、reorientation和rigorous reorientation(严格重排)吸附模型相结合,用于预测含活性分子油水界面张力及扩张流变的性质;结果表明,结合严格重排吸附模型能够准确地预测油水界面张力,界面扩张模量、相角、弹性和黏性模量随浓度、频率的变化趋势。

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.