| The spreading of fluids at the interface is widespread in nature and industry,and is the focus in many fields such as applied mathematics,geophysics,engineering,and biomedical engineering.It has broad application prospects in many engineering fields and biological processes.Fluid spreading has a wide range of scales,involving large-scale movement of celestial movement,continental ice sheet dynamics,lava flow,oil spill handling and coating flow,as well as liquid metal deformation,strengthening treatment,surface coating,drug delivery,tear flow and surfactant replacement therapy in the smallscales.In addition,the emerging fields of microfluidics and nanofluids also require technologies related to fluid spreading,such as the manufacture of standard microfluidic tools and the design of artificial biomaterials.These studies have attracted considerable attention,and significant progress has been made in experimental analysis and numerical research.In this paper,the research progress of the dynamics of fluid spreading on the liquid-liquid surface is described in detail,and the Marangoni effect caused by the surface tension gradient and the interface instability mechanism during the spreading process are mainly introduced.Different from surfactant-driven spreading,which is currently the most common subject of study,this paper observes the spreading process a low surface tension liquid on another liquid on a liquid substrate to understand the role of Marangoni effect in the spontaneous driving system,and realizes the liquid-driving control of spreading and instability mechanisms.First,a complex three-phase driven-spreading system is established,with silicone oil as the driving solvent,n-hexadecane as the driven solvent and aqueous solution as the substrate.Then the spreading process of n-hexadecane driven by silicone oil on the surface of different substrate solutions are observed and we discuss the influence of Marangoni flow caused by surface tension gradient during the liquiddriven spreading process.Experimental results show that the initial state of n-hexadecane is different on liquid substrates with different surface tensions.While the n-hexadecane drop stationed on the liquid surface is small,it is driven to form a rim and then breaks up into beads,which shows the Rayleigh-Plateau instability patterns.When we put the nhexadecane drop on the surface on the saturated sodium chloride solution,which spreads out more,it is driven to form a circular belt firstly and the Fingering instability subsequently occurs at the inner edge of the circular belt.The spreading process before instability is analyzed by establishing the scale law between the spreading radius of nhexadecane and the spreading time.Different stability analysis models are also used to analyze the Rayleigh-Plateau instability and Fingering instability.The characteristic parameters are theoretically deduced,and the results obtained from the theoretical analysis are compared with the experimental results.This paper also conducted experiments and theoretical analysis on other factors affecting the spreading of n-hexadecane driven by silicone oil.Studies show that such highly ordered spreading patterns are mainly driven by the surface tension gradient caused by the dripping of silicone oil.Also,the concentration of the substrate solution,volatility and viscosity of the driving solvent,and the environmental constraints have effects on the spreading.Studies have shown that the volatility of the driving solvent will reduce the scaling law of the spreading radius and time.The concentration of substrate solution,the viscosity of driving solvent and the size of environmental constraints are positively correlated with the maximum spreading radius. |
