Spreading Characteristics Of Droplet With Surfactant On Uneven Topography Under The Disjoining Pressure

The flow behavior of thin liquid film on the solid substrate shows rich dynamics characteristics, and its fracture mechanism and stability have always been hot issues of concern. Especially, when the thin liquid film containing surfactants, the dynamics of droplet spreading on preset films are also dominated by Marangoni stress, which drives liquid film flow from low surface tension areas to the areas of high surface tension, this feature have attracted considerable attention in literatures for the widely applications in biomedical processing, aerospace engineering and chemical engineering industries. When the thickness of the thin liquid film reduces to micro-nano level, the disjoining pressure exerts an important influence on its evolution characteristics. In this paper, the dynamics and stability of droplet evolution over uneven topography under the disjoining pressure are discussed via numerical simulation and theoretical analysis. The main parts of thesis are as follows:(1) For the spreading of an insoluble surfactant-laden droplet over corrugated topography, a disjoining pressure model induced by the concentration of the surfactant is established. The lubrication theory is applied to derive the evolution equations of droplet height and interfacial surfactant concentration. The droplet evolution process is numerically simulated via PDECOL program, and the effects of disjoining pressure on spreading dynamics characteristics over corrugated topography are analyzed.(2) Taking disjoining pressure into account, the spreading process of an insoluble surfactant-laden droplet over topography of differrent structures are simulated. The spreading characteristics of each structure are examined, and the influence of disjoining pressure on spreading rate of doplet on each substrate is compared.(3) Based on the non-modal stability theory, the base state and disturbance evolution equations over corrugated topography for the droplet height and surfactant concentrations are presented. Transient growth analysis(TGA) is carried out to investigate the stability of evolution process, and the effects of disjoining pressure on spreading characteristics and stability are explored.