Afsar-Siddiqui Abia B, Luckham Paul F, Matar Omar K
Department of Chemical Engineering & Chemical Technology, Imperial College London, SW7 2AZ, U.K.
Langmuir. 2004 Aug 31;20(18):7575-82. doi: 10.1021/la040041z.
Previous experimental work has shown that the spreading of a drop of aqueous anionic surfactant solution on a liquid film supported by a negatively charged solid substrate may give rise to a fingering instability (Afsar-Siddiqui, A. B.; Luckham P, F.; Matar, O. K. Langmuir 2003, 19, 703-708). However, upon deposition of a cationic surfactant on a similarly charged support, the surfactant will adsorb onto the solid-liquid interface rendering it hydrophobic. Water is then expelled from the hydrophobic regions, causing film rupture and dewetting. In this paper, experimental results are presented showing how the surfactant concentration and film thickness affect the dewetting behavior of aqueous dodecyltrimethylammonium bromide solutions. At low surfactant concentrations and large film thicknesses, the film ruptures at a point from which dewetting proceeds. At higher concentrations and smaller film thicknesses, the ruptured region is annular in shape and fluid moves away from this region. At still higher concentrations and smaller film thicknesses, the deposited surfactant forms a cap at the point of deposition that neither spreads nor retracts. This variation in dewetting mode is explained by considering the relative Marangoni and bulk diffusion time scales as well as the mode of assembly of the surfactant adsorbed on the solid surface.
先前的实验工作表明，阴离子表面活性剂水溶液滴在由带负电的固体基质支撑的液膜上的铺展可能会引发指进不稳定性（阿法尔 - 西迪基，A. B.；勒克姆，P. F.；马塔尔，O. K.《朗缪尔》2003年，第19卷，703 - 708页）。然而，当阳离子表面活性剂沉积在带相同电荷的载体上时，表面活性剂会吸附到固 - 液界面上，使其具有疏水性。然后水从疏水区域被排出，导致膜破裂和去湿。在本文中，展示了实验结果，表明表面活性剂浓度和膜厚度如何影响十二烷基三甲基溴化铵水溶液的去湿行为。在低表面活性剂浓度和大膜厚度下，膜在一个点处破裂，去湿从此处开始。在较高浓度和较小膜厚度下，破裂区域呈环形，流体从该区域移开。在更高浓度和更小膜厚度下，沉积的表面活性剂在沉积点形成一个帽状物，既不铺展也不回缩。通过考虑相对的马兰戈尼和体扩散时间尺度以及吸附在固体表面的表面活性剂的组装方式来解释这种去湿模式的变化。
