Laboratoire de Physique des Solides UMR 8502, Université Paris-Sud, 91405 Orsay, France.
Langmuir. 2012 Feb 28;28(8):3821-30. doi: 10.1021/la204386b. Epub 2012 Feb 16.
We present a large range of experimental data concerning the influence of surfactants on the well-known Landau-Levich-Derjaguin experiment where a liquid film is generated by pulling a plate out of a bath. The thickness h of the film was measured as a function of the pulling velocity V for different kinds of surfactants (C(12)E(6), which is a nonionic surfactant, and DeTAB and DTAB, which are ionic) and at various concentrations near and above the critical micellar concentration (cmc). We report the thickening factor α = h/h(LLD), where h(LLD) is the film thickness obtained without a surfactant effect, i.e., as for a pure fluid but with the same viscosity and surface tension as the surfactant solution, over a wide range of capillary numbers (Ca = ηV/γ, with η being the surfactant solution viscosity and γ its surface tension) and identify three regimes: (i) at small Ca α is large due to confinement and surface elasticity (or Marangoni) effects, (ii) for increasing Ca there is an intermediate regime where α decreases as Ca increases, and (iii) at larger (but still small) Ca α is slightly higher than unity due to surface viscosity effects. In the case of nonionic surfactants, the second regime begins at a fixed Ca, independent of the surfactant concentration, while for ionic surfactants the transition depends on the concentration, which we suggest is probably due to the existence of an electrostatic barrier to surface adsorption. Control of the physical chemistry at the interface allowed us to elucidate the nature of the three regimes in terms of surface rheological properties.
我们呈现了一系列关于表面活性剂对著名的朗道-莱维奇-德加古因实验影响的实验数据，该实验通过从浴池中拉出一个平板来产生液膜。对于不同类型的表面活性剂（C（12）E（6），一种非离子表面活性剂，以及 DeTAB 和 DTAB，这两种是离子型的）和在接近和高于临界胶束浓度（cmc）的各种浓度下，我们测量了膜厚 h 作为拉出速度 V 的函数。我们报告了增厚因子α=h/h（LLD），其中 h（LLD）是在没有表面活性剂影响的情况下获得的膜厚，即对于纯流体，但具有与表面活性剂溶液相同的粘度和表面张力，在广泛的毛细数（Ca=ηV/γ，其中η是表面活性剂溶液的粘度，γ是其表面张力）范围内，并确定了三个区域：（i）在小 Ca 时，由于限制和表面弹性（或马兰戈尼）效应，α很大；（ii）对于增加的 Ca，存在一个中间区域，其中α随着 Ca 的增加而减小；（iii）在更大（但仍然较小）的 Ca 时，由于表面粘度效应，α略高于 1。对于非离子表面活性剂，第二区域在固定的 Ca 处开始，与表面活性剂浓度无关，而对于离子表面活性剂，转变取决于浓度，我们认为这可能是由于表面吸附的静电障碍的存在。界面物理化学的控制使我们能够根据表面流变性质阐明三个区域的性质。
