Flow Characteristics Of The Solution With Insoluble Surfactant On Topographic Substrates

With the development of MEMS technology, microscale and nanoscale thin filmflow has attracted much attention in the field of fluid mechanics. For the microscaleresearch, surface tension, viscosity, topography feature and surfactant concentration havethe significant effects on liquid flows, which determines the quality and applicationperformance of products.In this paper, for the flow of the thin film or droplet with and without insolublesurfactant, theoretical models are established and the dynamics and stability of thin filmor droplet, as well as the effects of gravity, surfactant concentration and topographysurface property are analyzed with numerical simulation based on lubrication theory andnon-modal stability theory. The main contents of the paper are as following:(1) For the spreading of the droplet with insoluble surfactant over corrugatedtopography, the evolution equations of liquid film thickness and interfacial surfactantconcentration are derived. The droplet spreading characteristics and the combinedimpacts of surfactant concentration and topography structure are numerically simulatedwith PDECOL code. The stability of droplet spreading and the effects of differentparameters are investigated via non-modal stability theory.(2) For ultrathin liquid films flowing over topography surfaces, the evolutionequation of thin liquid film thickness under steady state is formulated. The variations ofultrathin liquid film thickness on different topography surfaces and the influence oftopography structure and gravity are investigated based on the numerical simulation withPDECOL code.(3) For the flow of an insoluble surfactant-laden thin film and droplet on inclinedrandom topography, the evolution equations of liquid film thickness and interfacialsurfactant concentration are presented. The roles of gravity, topography surfaceproperties and surfactant concentration on the characteristics of thin film flow anddroplet spreading, along with the variations of maximum film thickness and surfactantconcentration, are numerically simulated with PDECOL code.