Laboratoire de physique des solides, CNRS & Université Paris-Sud 11, 91405 Orsay cedex, France.
Langmuir. 2011 Nov 15;27(22):13406-9. doi: 10.1021/la202233f. Epub 2011 Oct 24.
Classical Frankel's law describes the formation of soap films and their evolution upon pulling, a model situation of film dynamics in foams (formation, rheology, and destabilization). With the purpose of relating film pulling to foam dynamics, we have built a new setup able to give an instantaneous measurement of film thickness, thus allowing us to determine film thickness profile during pulling. We found that only the lower part of the film is of uniform thickness and follows Frankel's law, provided the entrainment velocity is small. We show that this is due to confinement effects: there is not enough surfactant in the bulk to fully cover the newly created surfaces which results in immobile film surfaces. At large velocities, surfaces become mobile and then Frankel's law breaks down, leading to a faster drainage and thus to a nonstationary thickness at the bottom of the film. These findings should help in understanding the large dispersion of previous experimental data reported during the last 40 years and clarifying the pulling phenomenon of thin liquid films.
经典的 Frankel 定律描述了肥皂膜的形成及其在拉伸过程中的演变，这是泡沫中薄膜动力学的模型情况（形成、流变学和不稳定性）。为了将薄膜拉伸与泡沫动力学联系起来，我们建立了一个新的装置，能够对薄膜厚度进行瞬时测量，从而可以在拉伸过程中确定薄膜厚度分布。我们发现，只有薄膜的下部具有均匀的厚度并遵循 Frankel 定律，前提是夹带速度较小。我们表明，这是由于限制效应：在体积中没有足够的表面活性剂来完全覆盖新产生的表面，这导致了不可移动的薄膜表面。在较大的速度下，表面变得可移动，然后 Frankel 定律失效，导致薄膜底部的排水速度更快，从而导致厚度不再稳定。这些发现应该有助于理解过去 40 年来报告的大量实验数据的分散性，并阐明薄液膜的拉伸现象。
