Basheva Elka S, Kralchevsky Peter A, Danov Krassimir D, Ananthapadmanabhan Kavssery P, Lips Alex
Laboratory of Chemical Physics & Engineering, Faculty of Chemistry, University of Sofia, Sofia 1164, Bulgaria.
Phys Chem Chem Phys. 2007 Oct 14;9(38):5183-98. doi: 10.1039/b705758j.
Knowing the size and interactions of colloid particles, one can predict the stepwise thickness transitions and the contact angles of particle-containing liquid films. Here, we consider the inverse problem, viz. how to determine the particle properties by measurements with liquid films. We carried out experiments with films formed from aqueous solutions of two nonionic surfactants, Brij 35 and Tween 20, which contain spherical micelles of diameters in the range 7-9 nm. From the measured contact angles, we determined the micelle aggregation number and volume fraction. In addition, from the measured disjoining-pressure isotherms we determined the micelle diameter. In other words, the liquid-film measurements give information about the micelles, which is analogous to that obtainable by dynamic and static light scattering. Furthermore, we investigate the predictions of different quantitative criteria for stability-instability transitions, having in mind that the oscillatory forces exhibit both maxima, which play the role of barriers to coagulation, and minima that could produce flocculation or coalescence in colloidal dispersions (emulsions, foams, suspensions). The interplay of the oscillatory force with the van der Waals surface force is taken into account. Two different kinetic criteria are considered, which give similar and physically reasonable results about the stability-instability transitions. Diagrams are constructed, which show the values of the micelle volume fraction, for which the oscillatory barriers can prevent the particles from coming into close contact, or for which a strong flocculation in the depletion minimum or a weak flocculation in the first oscillatory minimum could be observed.
了解胶体颗粒的大小和相互作用后，人们可以预测含颗粒液膜的逐步厚度转变和接触角。在此，我们考虑相反的问题，即如何通过液膜测量来确定颗粒性质。我们用由两种非离子表面活性剂Brij 35和吐温20的水溶液形成的液膜进行了实验，这些溶液含有直径在7 - 9纳米范围内的球形胶束。根据测量的接触角，我们确定了胶束聚集数和体积分数。此外，根据测量的分离压力等温线，我们确定了胶束直径。换句话说，液膜测量给出了有关胶束的信息，这类似于通过动态和静态光散射可获得的信息。此外，我们研究了不同定量标准对稳定性 - 不稳定性转变的预测，同时考虑到振荡力既表现出最大值（其起到凝聚障碍的作用），也表现出最小值（这可能在胶体分散体系（乳液、泡沫、悬浮液）中产生絮凝或聚并）。考虑了振荡力与范德华表面力的相互作用。考虑了两种不同的动力学标准，它们对于稳定性 - 不稳定性转变给出了相似且符合物理常理的结果。构建了图表，展示了胶束体积分数的值，对于这些值，振荡障碍可以防止颗粒紧密接触，或者可以观察到在耗尽最小值处的强烈絮凝或在第一个振荡最小值处的微弱絮凝。
