Max-Planck Institute of Colloids and Interfaces, 14424 Golm/Potsdam, Germany.
Langmuir. 2010 Apr 6;26(7):4865-72. doi: 10.1021/la9036748.
We studied the process of thinning of thin liquid films stabilized with the nonionic surfactant n-dodecyl-beta-maltoside (beta-C(12)G(2)) with primary interest in interfacial diffusion processes during the thinning process dependent on surfactant concentration. The surfactant concentration in the film forming solutions was varied from 0.01 to 1.0 mM through the critical micellar concentration of 0.16 mM at constant electrolyte (NaCl) concentration, nominally 0.2 M. This assures the formation of Newton black films at the end of the thinning process. The velocity of thinning was analyzed combining previously developed theoretical approaches. From the model, which accounts for diffusion processes in the bulk of the film and in the interfaces, an analytical function was derived and fitted numerically to the experimental data. Quantitative information about the mobility of the surfactant molecules at the film surfaces could be obtained. We find that above a surfactant concentration of 0.12 mM (beta-C(12)G(2)) the film surfaces behave as immobile and nondeformable which decelerates the thinning process. This follows the predictions for Reynolds flow of liquid between two nondeformable disks. Moreover, we could apply the theory on free area dependent diffusion coefficients on our results and show that it is in reasonable ranges applicable on the used surfactant system.
我们研究了用非离子表面活性剂 n-十二基-β-麦芽糖苷（β-C(12)G(2)）稳定的薄液膜变薄的过程，主要关注变薄过程中表面活性剂浓度依赖性的界面扩散过程。在恒定电解质（NaCl）浓度下，通过 0.16mM 的临界胶束浓度，将成膜溶液中的表面活性剂浓度从 0.01mM 变化到 1.0mM，这确保了在变薄过程结束时形成牛顿黑膜。通过结合先前开发的理论方法来分析变薄速度。从该模型中，推导出了一个考虑到膜体和界面中的扩散过程的解析函数，并通过数值拟合实验数据进行拟合。可以获得有关表面活性剂分子在膜表面上的迁移率的定量信息。我们发现，在表面活性剂浓度高于 0.12mM（β-C(12)G(2)）时，膜表面表现为不可移动和不可变形，这会减缓变薄过程。这符合两个不可变形圆盘之间的雷诺流动对液体的预测。此外，我们可以将基于自由面积的扩散系数理论应用于我们的结果，并表明它在合理的范围内适用于所使用的表面活性剂体系。
