Numerical Simulation On Formation Of Film's Deposition And Expansion

It is a exploring subject of micro-fluid mechanics and difficult to investigate that the formation of droplet, impact on substrates and expansion over substrates'surface have close relationship with the variation of topology of matrices and characteristics of liquid during the deposition, expansion and formation of film. Droplet's formation, continuous drop, and deposit on different type of substrate using variant coating method are studied in this paper by making use of numerical simulation method in order to know more about the droplet formation and its expansion over substrate surface and investigate influences of defects on product quality. The contents of this paper focus on the following three parts:1,Film formation over smooth surface of different dimensional substrates is numerically simulated. The whole process of drop's forming and falling onto substrates and expansion over substrates driven by gravity and inertia force are studied. The influence of spin velocity of substrate, coating volume of droplet, surface tension coefficient and viscosity coefficient on film formation and its quality are analyzed. It is found that spin velocity of substrate, surface tension and viscosity coefficient are of visible influence on film quality and forming time. Spin velocity of substrate has important influence on film thickness, and the film will be more homogeneous when it increases linearly and slowly. When the viscosity is greater than 20 cp the pressure of film surface is unstable and prone to defects such as striation and so on.2,Numerical simulation of film formation process over non-smooth and inclined substrate are investigated, and the flow mechanism of free surface during film formation is studied. It is shown that the surface tension coefficient is of importance for solution expansion at surrounding area of specific surface topography. Larger surface tension coefficient makes against solution expansion and is prone to bring defects. Otherwise, the viscosity of solution is related with formation of boundary layer near wall area. When the velocity gradient is approach to zero the boundary layer is incidental to break away from wall. Larger flux of solution and velocity of expansion result in continuous film and thicker film, but don't affect shape of free surface at the specific surface topography evidently.3,The process of forming and falling in continuous drops and expansion over substrate surface are simulated. It is found that the variation of flux have serious influence on shape, volume and forming time of droplet. Variation of pressure affects droplet formation obviously, and the variation of temperature affects the forming time and volume of droplet little. When the formative droplets impact the substrate or film in sequence, there will be a pressure turning at the contact point because of severe impact. For different type of substrate the pressure generated by the impact are also different. Although the pressure on film substrate is less than solid one at the contact point, slight variation will result in film defects easily owing to intrinsic stability of film has been destroyed.