Combined flow and evaporation during spin coating of complex solutions

Abstract

The flow and evaporation behavior from complex solutions during spin coating have been measured. Methanol/butanol mixtures where chosen as a controlled case-study for intensive evaluation. In addition, a sample sol—gel was evaluated using the same techniques. It was found that binary solutions had two identifiable thinning regions. At first, the thinning behavior is governed by the viscosity and evaporation rate of the starting mixture. However, near the end of the spinning process, the evaporation of the more volatile component has caused the fluid composition to change (toward the less volatile solution member). Therefore, the thinning behavior at the end displays a transition which approaches that of the pure end-member. The thinning behavior for the sol—gel precursor solution was linear until quite close to the gelation point, suggesting that further analysis of sol—gel solutions would be fruitful using this technique.