Solvent diffusivity, spin coating process

Bornside et al. [138] have developed a model for spin coating in which evaporation has been analyzed in terms of the mass flux (or mass transfer) from the liquid phase into the adjacent gas phase. Such a mass flux is controlled by a convection-diffusion process that depends on the solution concentration that increases as the solvent leaves the liquid phase. The characteristics of the gas phase in the close vicinity may also have a speciflc effect on the evaporation process. A modifled model based on the equations of Meyerhofer and Bornside was used by Chang et al. [123] to predict the fllm thickness of spin-coated polymers. In their model, two equations were used one to predict the wet fllm thickness, h, after spin coating but before drying and another to determine the final fllm thickness (hf). The film thicknesses that they have theoretically predicted agree well with those experimentally determined, especially in solutions of low polymer concentration. 

Solution processes are used mainly for coating, film casting and fibre spinning, i.e. in processes where the distance the solvent has to diffuse out of the solution once coated, cast or spun is short. Regulation of this diffusion process is important if products of even quality are to be obtained. 

---