Flow Characteristics Of Thin Film Containing Insoluble Surfactant Over Topography Surface

In recent years, the development of MEMS technology attracts much attention on the fields of microscale and nanoscale altrathin film flows. With the reducing of research scale, variations of surface tension, caused by topography feature and surfactant concentration, have significant effects on liquid flows, which determines the quality and application performance of products.In this paper, for the flowing of thin film or a droplet containing insoluble surfactant over uneven substrate, the lubrication theory is adopted to establish the evolution equations for liquid film thickness and interfacial surfactant concentration. The film flowing characteristics and the effects of related parameters are numerically simulated. And the stability of the droplet spreading is investigated based on the non-model stability theory. The main contents of the paper are listed as follows:(1) For the flowing of thin film with insoluble surfactant over grooving topography, the evolution equations of liquid film thickness and interfacial surfactant concentration are derived under steady state. The film flowing characteristics and the combined impacts of surfactant concentration and topography structure are numerically simulated with PDECOL code. And the effects of related parameters and relevant force are examined.(2) For ultrathin liquid films flowing over periodic topography surfaces, the evolution equation of thin liquid film thickness is formulated. The liquid film flow characteristics on up-hilling and down-hilling processes are discussed, as well as the influence of conjoining and disjoining pressure.(3) For the spreading of liquid droplet containing insoluble surfactant over two-dimensional micropillar arrayed topography surface, the lubrication theory is used to derive the evolution equations of liquid film thickness and interfacial surfactant concentration. The droplet spreading characteristics and the effects of related parameters are numerically explored.(4) For the spreading of a droplet covered with insoluble surfactant over inclined random heterogenous substrates, the base state and disturbance evolution equations of film thickness and surfactant concentration are presented. Under the actions of gravity, Marangoni force, and capillary force related to topography surface properties, the stability of the droplet spreading on heterogenous substrates and the effects of dimensionless parameters as well as its internal mechanism are analyzed based on the non-model stability theory.