Abstract: A liquid film of thickness less than 100 nm with soluble surfactant is subject to disjoining pressure or conjoining pressure induced by intermolecular forces,which determines its stability and wettability.In the present paper,based on three nonlinear partial differential evolution equations for film thickness,surfactant interfacial concentration and bulk concentration derived from the lubrication theory,the processes of droplet spreading driven by surfactant under the action of intermolecular forces in positive and negative systems were simulated numerically,and the effect of intermolecular forces,collectively called disjoining pressure or conjoining pressure,was analyzed.Disjoining pressure promoted droplet spreading stably and inhibited film dewetting occurrence in a positive system; disjoining pressure played a destabilizing role in a negative system by amplifying perturbations,and changing the effect of Marangoni stress.The droplet in a positive system presented unstable evolution characteristics under conjoining pressure,which led to film rupture ultimately; in a similar effect with disjoining pressure,conjoining pressure further enhanced the instability of droplet evolution in a negative system.

Key words: soluble surfactant, droplet, spreading, disjoining pressure, conjoining pressure

摘要： 当含活性剂液膜厚度小于100 nm时,分子间力表现出的分离压或结合压效应将对其演化特征及去润湿特性产生重要影响。针对可溶性活性剂液滴的铺展历程,采用润滑理论建立了液膜厚度、活性剂表面浓度和内部浓度的演化模型,模拟了正负体系中受分离压或结合压影响的液滴演化过程。结果表明,分离压可促进正体系下的液滴稳定铺展,并抑制去润湿现象的发生;而负体系下,分离压则加剧不稳定性,并改变Marangoni负效应对液滴演化的影响。正体系下液滴受结合压作用呈现不稳定特征,在极短时间内发生破断;结合压对负体系下的液滴演化影响与分离压作用相似,具有促进液滴不稳定演化的作用。

关键词: 可溶性活性剂, 液滴, 铺展, 分离压, 结合压