含活性剂液膜去润湿演化的稳定性特征

Stability characteristics of thin film dewetting with insoluble surfactant

针对含非溶性活性剂的液膜在固体基底上的去润湿过程,基于润滑理论建立了基态和扰动态下液膜厚度和表面活性剂浓度的演化模型,应用非模态理论分析了演化过程的稳定性特征,探讨了分子间力对液膜去润湿过程的影响.研究表明,微扰动波的引入(k=1)有利于液膜去润湿过程的稳定进行,扰动能量逐渐衰减,然而,该效果随着扰动波数的增加而显著改变,k 2时,液膜演化的稳定性反而恶化,扰动能量被逐步放大,演化呈现出非稳定特征.增大初始液膜厚度可以有效改善液膜流动的稳定性.范德华力放大了液膜表面的微扰动,使得液膜演化的稳定性下降;相反,Born斥力和静电斥力具有增强去润湿稳定性的作用.

Considering the process of insoluble-surfactant-laden film dewetting on a solid substrate, we have established the base state and disturbance evolution equations for the film thickness and interfacial surfactant concentrations based on the lubrication approximation. Transient growth analysis （TGA） was carried out to investigate the stability characteristics of evolution process, and the effects of intermolecular forces were discussed. Results indicate that the introduction of disturbance wave for k=1 is conducive to enhance the stability of film evolution, and the disturbance energy gradually decays; however, the effect changes unexpectedly with the increment of wave number： when k ≥ 2, the stability of dewetting process is deteriorated while disturbance energy grows by degrees and the film flow shows unstable characteristics. Thickening the initial film thickness can effectively improve the stability of film dewetting. Van der Waals force enlarges the disturbance on the film surface and leads to the decline of stability. Conversely, Born force and electrostatic force are propitious for the film evolving stably.