Evaporation Behaviour of a Thinning Liquid Film in a Spin Coating Setup: Comparison Between Calculation and Experiment
AbstractWe present and analyze comprehensive measurements of the evaporation behavior, E, of a thinning liquid film during a hydrodynamic-evaporative spin coating experiment. E, ω (the rotation speed), and ν (the liquid viscosity) are the main control parameters of the process. The entire film thinning process can be described theoretically quite well if these parameters are known. Values of ν are easily accessible in advance (calculations, literature values, measurements). Values for E can essentially not be found in the literature. They are hard to measure and specific for the experimental conditions. There is also no generally accepted strategy to calculate E. Our experimental results are compared with a theoretical prediction for E based on ideas by Bornside, Macosco, and Scriven, which were presented long ago. Their approach was never tested experimentally. Theory and experiment agree well for many solvents and different ω. This approach permits in advance the quantitative calculation of the evolution of the entire hydrodynamic-evaporative film thinning process. We also derive a general formula to predict ab initio, with literature data only, the amount of final deposit (film thickness) of solute in the case of spin coating mixtures of volatile solvents and nonvolatile solutes.