Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Langmuir. 2010 Aug 17;26(16):13310-9. doi: 10.1021/la101870m.
Diffusion of surfactant to a spherical interface depends on the radius of curvature of the interface; the smaller the radius of curvature is, the faster the dynamics. This paper presents and validates an experimental apparatus, denoted a "microtensiometer", to study the dependence of surfactant dynamics on radius of curvature. Dynamic surface tension is monitored for a range of bubble radii from 17 to 150 microm, and the dynamics are compared with those obtained using the classic pendant drop experiment for a nonionic surfactant at the air-water interface. Experiments reveal that dynamic surface tension follows a diffusion-limited scaling, in which radius of curvature is a key parameter. Despite the clear scaling behavior of the experimental equilibration time, the full dynamic curve for an initially clean interface cannot be predicted by a diffusion-limited transport model using the molecular diffusion coefficient and a single isotherm. However, the same model is shown to correctly predict compression-expansion experiments. Aside from elucidation of surfactant transport, this device provides a tool for rapid measurements of interfacial properties using a significantly lower volume of sample than current methods.
表面活性剂向球形界面的扩散取决于界面的曲率半径；曲率半径越小，动力学过程越快。本文提出并验证了一种实验装置，称为“微张力计”，用于研究表面活性剂动力学与曲率半径的关系。研究了气泡半径范围从 17 到 150 微米的动态表面张力，将动力学与空气-水界面上非离子表面活性剂的经典悬滴实验的动力学进行了比较。实验表明，动态表面张力遵循扩散限制的标度，其中曲率半径是一个关键参数。尽管实验平衡时间具有明显的标度行为，但使用分子扩散系数和单个等温线的扩散限制输运模型无法预测初始清洁界面的完整动态曲线。然而，同样的模型被证明可以正确预测压缩-扩张实验。除了阐明表面活性剂的输运外，该装置还提供了一种工具，用于使用比当前方法少得多的样品量快速测量界面性质。
